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Photochemistry of tetrahydro-1, 4-naphthoquinones in the solid state Dzakpasu, Alice Afi 1977

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PHOTOCHEMISTRY OF TETRAHYDRO-1,4- . NAPHTHOQUINONES IN THE SOLID STATE by ALICE AFI DZAKPASU B . S c , Stanford University, 1969 M.Sc., U n i v e r s i t y of C a l i f o r n i a , Los Angeles, 1971 Lecturer i n Chemistry, U n i v e r s i t y of Cape Coast, Ghana, 1971-74  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY  i n the Department of CHEMISTRY  We accept t h i s t h e s i s as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1977  <£) A l i c e A f i Dzakpasu, 1977  In p r e s e n t i n g t h i s  thesis  an advanced degree at  further  fulfilment  of  the  requirements  the U n i v e r s i t y of B r i t i s h Columbia, I agree  the L i b r a r y s h a l l make it I  in p a r t i a l  freely  available  for  this  thesis  f o r s c h o l a r l y purposes may be granted by the Head of my Department  of  this thesis for  It  financial  The  of  gain s h a l l not  Chemistry  U n i v e r s i t y of B r i t i s h Columbia  2075 Wesbrook Place Vancouver, Canada V6T 1W5  or  i s understood that copying or p u b l i c a t i o n  written permission.  Department  that  reference and study.  agree t h a t p e r m i s s i o n for e x t e n s i v e copying o f  by h i s r e p r e s e n t a t i v e s .  for  be allowed without my  ii  To Professor John I. Brauman who  taught and  me to the  introduced  fascinating  world of organic Chemistry.  - iii -  Abstract  Previous investigations i n v o l v i n g the behaviour of c i s 4a,5,8,8a-tetrahydro-l,4-naphthoquinone  and i t s d e r i v a t i v e s i n  s o l u t i o n under UV i r r a d i a t i o n raised the question of what r o l e , i f any, the ground state conformations of these molecules play i n a) the type of photochemical behaviour the substrate e x h i b i t s and b) the product d i s t r i b u t i o n i n cases where more than one product i s formed. In a d d i t i o n , i t has never been established experimentally  just what  the geometric requirements f o r the various reactions encountered i n t h i s s e r i e s are.  Such requirements usually provide i n s i g h t s into  geometry of the t r a n s i t i o n state i t s e l f .  the  In the s o l i d state, the  i n i t i a l conformation of molecules of any given substrate can be accurately determined by s i n g l e c r y s t a l X-ray d i f f r a c t i o n methods. Furthermore, since the c r y s t a l l a t t i c e usually r e s i s t s any gross changes i n conformation during the course of a r e a c t i o n , i t follows that most reactions i n the c r y s t a l l i n e state w i l l occur from the ground state conformation of the substrate. By studying these reactions i n the s o l i d state and c o r r e l a t i n g the r e s u l t s with the X-ray data, i t was hoped that the questions raised as well as others e.g. concentration e f f e c t s could be answered.  - iv -  Eleven substrates were chosen f o r the i n v e s t i g a t i o n .  They  were a l l prepared by the D i e l s Alder addition of a diene to a quinone. By slow c r y s t a l l i z a t i o n a l l substrates with the exception of 6,7dimethyl-4a3,5,8,8a3-tetrahydro-l,4-naphthoquinone,  1_ and  2,3,4aB,5a,8a,8a3-hexamethyl-4a3,5,8,8a3-tetrahydro-l,4-naphthoquinone, 10, gave c r y s t a l s s u i t a b l e f o r single c r y s t a l X-ray structure determination. Relevant X-ray data of nine of these substrates and f i v e of the s o l i d state photoproducts are reported. In the s o l i d state,  5a,8a-dimethyl-4a8,5,8,8a3-tetrahydro-  1,4-naphthoquinone, _1, 6,7-dimethyl-4a3,5,8,8ag-tetrahydro-l,4naphthoquinone, 2_, and the parent compound 4a3,5,8,8a3-tetrahydro1,4-naphthoquinone, _3, did not undergo the photochemical intramolecular hydrogen a b s t r a c t i o n they undergo i n s o l u t i o n .  Instead, they  dimerized s t e r e o s p e c i f i c a l l y to t h e i r respective centrosymmetric dimers when i r r a d i a t e d with UV l i g h t below t h e i r respective e u t e c t i c temperatures.  This i s r a t i o n a l i z e d i n terms of a p a r a l l e l  alignment  of the C ( 2 ) , C ( 3 ) double bonds of adjacent monomers and short intermolecular centre-to-centre separation (<4.040A)  of these double  bonds. Five of the substrates, namely, 6,7-diphenyl-4a3,5,8,8a3tetrahydro-1,4-naphthoquinone, 9,10-anthraquinone, 6^  4_, 2,3-dimethyl-l, 4-4a3, 9a3~tetrahydro-  4a3,8a3-dicyano-6,7-dimethyl-4a3,5,8,8a3-  tetrahydro-1,4-naphthoquinone,  1_,  2,3,4a3,6,7,8a3-hexamethyl-  4a3,5,8,8a3-tetrahydro-l,4-naphthoquinone,  9_ and 2,3,4a3,5S,83,8a3-  -  V  -  hexamethyl-4a8,5,8,8ae-tetrahydro-l,4-naphthoquinone,  11 have  intermolecular double bond contacts exceeding 4 . l l and d i d not undergo dimerization i n the s o l i d state.  Instead, upon UV i r r a d i a t i o n ,  they formed t r i c y c l i c enone alcohols derived from intramolecular abstraction by oxygen of the C(8) hydrogen which l i e s i n the plane of the C(1)=0(1) carbonyl group.  Substrates 9_ and 11, i n addition, each gave a  t r i c y c l i c diketone r e s u l t i n g from the abstraction of one of the C5 hydrogens by C2.  The geometric requirements, the geometries of the  t r a n s i t i o n states and intermediates and the factors governing the modes of closure of the b i r a d i c a l intermediates i n both of these "hydrogen abstraction reactions and t h e i r implications for other hydrogen abstractions such as the Norrish Type II are discussed. One substrate, namely,  4a3,8aB-dicyano-5a,8a-dimethyl-  4a3,5,8,8aB-tetrahydro-l,4-naphthoquinone, j8, which lacks short intermolecular double bond contacts and has i t s C(8) hydrogen out of plane and f a r removed from the C(1)=0(1) group neither dimerized nor gave hydrogen abstraction products when i r r a d i a t e d i n the s o l i d state. Instead, i t gave an oxetane r e s u l t i n g from an intramolecular [^2+^2] addition of C(1)=0(1) to the C(6)=C(7) double bond. ' The intermolecular o  double bond contact here was 3.20A. L a s t l y , 2,3,6,7-tetramethyl-4aB,5,8,8a6-tetrahydro-l,4naphthoquinone, 5_, and 2,3,4agj5a,8a,8a3-hexamethyl-4ag,5,8,8agtetrahydro-l,4-naphthoquinone, 10, f a i l e d to react when i r r a d i a t e d i n the s o l i d state. The reason for t h i s i s not clear but the p o s s i b i l i t y of deexcit a t i o n v i a excimer formation and subsequent d i s s o c i a t i o n i s raised.  - vi -  Table of Contents Page INTRODUCTION 1.  2.  1  General  1  X-ray D i f f r a c t i o n Methods  2  Defects i n Crystals and Their E f f e c t s on Chemical Reactivity  3  Energy Transfer i n Organic Solids  17  Photochemistry of Tetrahydro-1,4-naphthoquinone and I t s Derivatives  19  B i r a d i c a l vs Charge-Transfer Mechanisms  26  C h a r a c t e r i s t i c s of the 3- and y-Hydrogen Abstraction Reactions i n the Tetrahydro-1,4-naphthoquinone Series:  3.  Substituent E f f e c t s  34  Solvent E f f e c t s  37  Quantum Y i e l d and Quenching Studies  39  Stereoelectronic Requirements  40  Other Reactions  41  Objectives of Present Research  41  RESULTS AND DISCUSSION  47  Preparation of Substrates 1.  Intermolecular [ 2 + TT  47  2] Dimerization: IT  •'•  5a,8a-Dimethyl-4aS,5,8,8ag-tetrahydro-l,4naphthoquinone, 1  54  6,7-Dimethyl-4aB,5,8,8ag-tetrahydro-l,4-naphthoquinone, 2  60  4ag,5,8,8a8-Tetrahydro-l,4-naphthoquinone, 3_  64  - v i i-  Page I r r a d i a t i o n of 2  i  n  Solution  Reactive State and Mechanism f o r Photodimerization 2.  3.  81  Intramolecular Hydrogen Abstraction: 6,7-Diphenyl-4aB,5,8,8aB-tetrahydro-l,4-naphthoquinone, 4  85  2.3- Dimethyl-l,4,4ag,9ag-tetrahydro-9,10-anthraquinone, 6  96  6,7-Dimethyl-4ag,8ag-dicyano-4ag,5,8,8ag-tetrahydro1.4-naphthoquinone, ]_  99  2,3,4ag,6,7,8ag-Hexamethyl-4ag,5,8,8ag-tetrahydro1,4-naphthoquinone,  107  2,3,4ag,5 B,8g,8aB~Hexamethyl-4aB,5,8,8ag-tetrahydro1,4-naphthoquinone, 11  114  The Geometry of the T r a n s i t i o n State f o r B- and y Hydrogen Abstractions  121  Intramolecular Oxetane Formation: 4ag,8ag-Dicyano-5a,8a-dimethyl-4aB,5,8,8aB-tetrahydro1,4-naphthoquinone, 8^  4.  80  Unreactive  134  Substrates:-.  2,3,6,7-Tetramethyl-4aB,5,8,8aB-tetrahydro-l,4naphthoquinone, _5  143  2,3,4aB,5a,8a,8aB-Hexamethyl-4aB,5,8,8aB-tetrahydro1,4-naphthoquinone, 10  149  EXPERIMENTAL BIBLIOGRAPHY APPENDIX  156 ;  211 221  - viii -  L i s t of Tables Table #  Caption  Page  I  UV Absorptions  25  II  Product Ratios Obtained i n Benzene and t e r t - B u t y l Alcohol  38  III  Substrates and Reaction Types Observed i n Solution  45  IV  Product Y i e l d s f o r the 1  IA Conversion  59  V  Product Y i e l d s f o r the 2_ -> 2A Conversion  63  VI  Product Y i e l d s f o r the _3 -»• 3A Conversion  64  VII  Product Y i e l d s f o r the /4(g) -*• 4A + 4B Conversion  88  VIII  Product Y i e l d s f o r the 4solution  4A + 4B Conversion ..  91  IX X  S p e c i f i c Rotation of Solutions of Crystals of 7A Product Ratios and Combined Yields f o r the 9_ -»• 9A + 9B Conversion i n the S o l i d State  105  XI XII  108  Product Ratios f o r the 9^ -> 9A + 9B Conversion i n Solution  109  Product Y i e l d s and Ratios f o r the 11 -> 11A + Conversion  115  11B  XIII  E f f e c t s of Structure on the McLafferty Rearrangement ...  123  XIV  Interatomic Distances, A, and Approach Angles f o r Hydrogen Abstraction  129  Intramolecular C(1)=0(1)•C(6)=C(7) Bond Contacts and Orientation  139  UV Absorption Spectra of Substrates 1-11  235  XV  XVI  - ix -  L i s t of Schemes Scheme //  Page  1  12  2  13  3  14  4  15  5  21  6  23  7  29  8  32  9  33  10  35  11  36  12  40  13  87  14  95  15  98  16  102  17  111  18  113  19  119  20  ...  131  21  147  22  149  - x -  List Figure ii  of Figures  Caption  Page  1  Vacancy; I n t e r s t i t i a l  2  Model of a simple cubic l a t t i c e  3  Voids and D i f f u s i o n  4  Ground state,  5  Operational D e f i n i t i o n of the Angle T  6  Uncorrected Endothermic E u t e c t i c Mixture  7  Stereo diagram of an adjacent p a i r of molecules of 5a,8a-dimethyl-4a3,5,8,8ag-tetrahydro-1,4naphthoquinone, 1  8  9 10  n,ir*  Atom  4 and d i s l o c a t i o n s  5 8  and  TT,TT*  states  28 42  T r a n s i t i o n f o r 1 + IA  Stereo diagram of dimer IA i n an o r i e n t a t i o n  52  55  analogous  to that of the monomer, 1^  57  Stereo diagram of dimer 2A  62  Infrared spectra of KBr p e l l e t s containing 4-5%  by  weight of dimer 3A (Top) and dimer 3B (Bottom)  67  11  Stereo diagram of the 3B molecule  69  12  Part of the absorption spectrum of benzene  73  13  Stereo diagram of compound j} Stereo diagram of neighbour related Stereo diagram of neighbour related  14 15  the contents of the u n i t c e l l for 76 molecule type A and i t s nearest by a simple c e l l t r a n s l a t i o n a type B molecule and i t s nearest by a centre of symmetry, X  16  Stereo diagram of compound 4^  17  (a) A 100 MHz PMR Spectrum of 2,3-Diphenyltricyclo[5.3.0.0 » ]deca-2-ene-6,9-dione, 4B (b) A 100 MHz PMR Spectrum of 2,3-Dimethyltricyclo[5.3.0.0 » ]deca-2-ene-6,9-dione, 2C  77 77 86  5  10  90  5  10  90  - xi -  Figure it  Caption  Page  18  Stereo diagram of compound 6_  98  19  Stereo diagram of compound ]_  100  20  Stereo diagram of enone-alcohol, 7A  104  21  Neighbouring ene-dione systems of a p a i r of molecules of 1_ .  106  22  Stereo diagram of substrate 9_  110  23  Stereo diagram of substrate 11  118  24  (a) Ground state geometry of substrate 9_ (b) The proposed t r a n s i t i o n state geometry for the  132  9^  .132  9B conversion  25  Stereo diagram of substrate J3  26  Approach geometry of the C(1)=0 and C(6)=C(7) ir bonds...  27  Stereo diagram of oxetane 8A  137  28  Stereo diagram of substrate 5_  143  29 30  Two adjacent molecules of 5_ within a c r y s t a l l o g r a p h i c cell The r e a c t i o n cavity before r e a c t i o n  145 152  31  Apparatus f o r i r r a d i a t i o n s i n the s o l i d state  165,166  32  Apparatus f o r low temperature i r r a d i a t i o n s i n solutions  170  A 60 MHz PMR spectrum of 5a,8a-dimethyl-4aB,5,8,8agtetrahydro-1,4-naphthoquinone, _1  221  Fourier transform 100 MHz PMR spectrum of 5,8,15,18tetramethylpentacyclo[10.8.0.0 » .0 » .0 > ]eicosa6,16-dien-3,10,13,20-tetrone, IA  221  A 60 MHz PMR spectrum of 6,7-dimethyl-4ag,5,8,8agtetrahydro-1,4-naphthoquinone, 2_  222  Fourier transform 100 MHz PMR spectrum of 6,7,16,17tetramethylpentacyclo[10.8.0.0 » .0*» .0 » ]eicosa6,16-dien-3,10,13,20-tetrone, 2A  222  33 34  136  2  35 36  2  11  11  4  9  14  9  14  136  19  19  - xii -  Figure // 37  38  Caption A 60 MHz PMR spectrum of 4ag,5,8,8ag-tetrahydro-l,4naphthoquinone, 3^  223  Fourier transform 100 MHz PMR spectrum of pentacyclo[10.8.0.0 > .0 » .0 ' ]eicosa-6,16-diene-3,10,13,20tetrone, 3A  223  A 60 MHz PMR spectrum of 6,7-diphenyl-4ag,5,8,8agtetrahydro-1,4-naphthoquinone, h_  224  A 100 MHz PMR Spectrum of l-hydroxy-7,8-diphenyltricyclo[5.3.0.0 » ]deca-2,8-dien-4-one, 4A  224  A 60 MHz PMR spectrum of 2,3,6,7-tetramethyl4ag,5,8,8ag-tetrahydro-l,4-naphthoquinone, 5_  225  A 60 MHz PMR spectrum of 2,3-dimethyl-l,4,4ag,9agtetrahydro-9,10-anthraquinone, 6^  226  A 100 MHz PMR spectrum of l-hydroxy-2,3-benzo-7,8dimethyltricyclo[5.3.0.0 > ]deca-8-ene-4-one, 6A  226  A 60 MHz PMR spectrum of 4ag,8ag-dicyano-6,7-dimethyl4ag,5,8,8ag-tetrahydro-l,4-naphthoquinone, ]_  227  A 100 MHz PMR spectrum of l-hydroxy-5,10-dicyano-7,8dimethyltricyclo[5.3.0.0 »l°]deca-2,8-dien-4-one, 7A ...  227  A 60 MHz PMR spectrum of 4a3,8ag-dicyano-5a,8adimethyl-4a$,5,8,8aB-tetrahydro-1,4-naphthoquinone,  228  2  39  40  11  4  5  41 42 43  9  14  19  10  5  44 45  Page  lu  5  46 47  48 49  J3 ..  A 100 MHz PMR spectrum of 5,10-dicyano-6,9-dimethyl11-oxatetracyclo [ 6 • 2.1.0-*-»?. 0^»10] undec-2-ene-4-one, 8A ,  228  A 60 MHz PMR spectrum of 2,3,4ag,6,7,8aB-hexamethyl4ag,5,8,8ag-tetrahydro-l,4-naphthoquinone, 9_  229  A 100 MHz PMR spectrum of l-hydroxy-2,3,5,7,8,10hexamethyltricyclo[5.3.0.0^ > ]deca-2,8-dien-4-one, 9A  229  A 100 MHz PMR spectrum of 2,3,5,7,8,10-hexamethyltricyclo[6.2.0.0 » 0]deca-2-en-6,9-dione, 9B  230  A 60 MHz PMR spectrum of 2,3,4ag,5a,8a,8ag-hexamethyl4ag,5,8,8ag-tetrahydro-l,4-naphthoquinone,  231  10  50  5  51  1  - xiii -  Figure  52  53  54  ff  Caption  Page  A 60 MHz PMR spectrum of 2,3,4ae,5g,8g,8ag-hexamethyl4ag,5,8,8ag-tetrahydro-l,4-naphthoquinone, 11  232  A 100 MHz PMR spectrum of l-hydroxy-2,3,5,6,9,10hexamethyltricyclo[5.3.0.0^ »1°]deca-2,8-dien-4-one, 11A  232  A 100 MHz PMR spectrum of 1,4,5,7,8,10-hexamethyltricyclo[6.2.0.0 »l°]deca-2-en-6,9-dione, 11B; (a) 1000 Hz sweep width; (b) 250 Hz sweep width of the 6.5-5.256 region with amplitude magnification of x l O ; (c) 250 Hz sweep width of the 3.05-0.86 region  233  Fourier transform 100 MHz PMR Merck Sharp & Dohme  234  5  55  spectrum of  CDCI3  from  - xiv -  Acknowledgement  My s i n c e r e thanks t o my r e s e a r c h d i r e c t o r , D r . J.R. S c h e f f e r , f o r a r o u s i n g and s u s t a i n i n g my i n t e r e s t i n t h i s a r e a o f r e s e a r c h t h r o u g h many i n v a l u a b l e d i s c u s s i o n s and f o r h i s h e l p f u l during the preparation of t h i s  suggestions  manuscript.  I am g r e a t l y i n d e b t e d t o D r . James T r o t t e r and D r . Simon E.V. P h i l l i p s who c a r r i e d o u t a l l t h e X - r a y s t r u c t u r e d e t e r m i n a t i o n s r e p o r t e d i n t h i s work.  I t r e a l l y was a p l e a s u r e c o l l a b o r a t i n g w i t h  s u c h a f i n e , z e a l o u s team.  I a l s o thank D r . S t e v e J . R e t t i g who,  w i t h D r . T r o t t e r , h e l p e d me w i t h some o f t h e c a l c u l a t i o n s i n v o l v e d . I am a l s o i n d e b t e d t o o t h e r members o f t h e t e a c h i n g s t a f f o f t h i s department e s p e c i a l l y D r . R.E. P i n c o c k and D r . E.A. O g r y z l o f o r t h e i r h e l p f u l suggestions during the i n i t i a l stages of t h i s r e s e a r c h and f o r b e i n g so generous w i t h some o f t h e i r i n s t r u m e n t s . My t h a n k s t o t h e m e c h a n i c a l team o f t h e t e c h n i c a l s t a f f o f t h i s department e s p e c i a l l y Mr. B. P o w e l l and Mr. M. Symonds who h e l p e d d e s i g n and b u i l d t h e p h o t o c h e m i c a l r e a c t o r w h i c h was used f o r the s o l i d s t a t e r e a c t i o n s . I w o u l d a l s o l i k e t o thank my f o r m e r and p r e s e n t c o l l e a g u e s o f l a b o r a t o r y 346 f o r t h e i r f r i e n d l i n e s s and c o o p e r a t i o n .  -  XV  -  My thanks to the Canadian Commonwealth Scholarship and Fellowship Association for t h e i r award (1974-77) and to the U n i v e r s i t y of Cape Coast,Ghana f o r granting me study leave from my  teaching  duties to undertake t h i s p r o j e c t . Last, but not l e a s t , my special thanks to Louise Hon typed t h i s manuscript.  who  - 1 -  Introduction  General  v  Organic s o l i d s , being generally low melting and complex as compared to metals, are more prone to c r y s t a l than the l a t t e r .  imperfections  It i s , therefore, not s u r p r i s i n g that the Journal of  Solid State Chemistry i s e x c l u s i v e l y inorganic.  While this a t t i t u d e of  s o l i d state chemists and p h y s i c i s t s i s , perhaps, understandable, the aloofness of organic chemists themselves from t h i s area of i s s u r p r i s i n g since most organic compounds are s o l i d s .  research  For, although  i t i s true that l i m i t e d d i f f u s i o n of reactants i n the s o l i d state places r e s t r i c t i o n s on the type of reactions which can occur, i t i s , nevertheless, also true that many unimolecular  and polymerization  reactions occur v i a  mechanisms which require no assistance from solvents.  The elimination  of the use of solvents from such systems i s not only b e n e f i c i a l i n terms of cost but also i n minimizing secondary reactions and reducing  the number of factors which need to be considered  in  i n proposing  mechanisms. Organic s o l i d state reactions have occasionally appeared i n the l i t e r a t u r e since 1880  but the c o r r e l a t i o n of r e a c t i v i t y with structure  of organic compounds became possible only a f t e r improved methods i n  - 2 -  X-ray crystallography became a v a i l a b l e .  X-ray D i f f r a c t i o n Methods^  When X-rays are passed through matter, some of the rays are scattered or d i f f r a c t e d , some are absorbed. analysis  r e l i e s on the recording and  i n t e n s i t i e s of the d i f f r a c t e d rays.  X-ray c r y s t a l structure  analyses of accurate values of The  the  i n t e n s i t y determinations  can be made on a single c r y s t a l or on a f i n e powder composed of small grains.  The  powder method has  serious drawbacks the greatest of which  i s the inherent lack of resolving originating  from d i f f e r e n t points i n the c r y s t a l and which are  symmetrically related  of i n t e n s i t y data from t h i s method more  Powder d i f f r a c t i o n methods are, therefore, unsuitable for  c r y s t a l s having large c e l l s and structure analyses.  - 1.0 mm  are hardly ever used for complex  Organic c r y s t a l s are invariably  the s i n g l e - c r y s t a l method. 0.1  not  to f a l l together or coincide as a single spot.  This makes the i n t e r p r e t a t i o n difficult.  power which causes r e f l e c t i o n s  investigated  by  In t h i s method, a single c r y s t a l measuring  on a side i s mounted on a goniometer head and  photographs are taken at varying angles using Weissenberg  several and  precession cameras. From these photographs the dimensions of the  unit  c e l l and also the space group to which the c r y s t a l structure belongs are determined.  Next, d i f f r a c t i o n i n t e n s i t i e s are recorded using an  automatic diffractometer. are derived and methods.  Using these i n t e n s i t i e s , the structure  t h e i r respective phases determined by  These l a t t e r quantities  factors  statistical  allow for the c a l c u l a t i o n of  electron  - 3 -  density maps from which the positions and nature of the atoms may determined.  be  Because of the u n c e r t a i n t i e s involved In pinpointing an  atom from electron density maps, the r e s u l t i n g structure i s only approximate.  This approximate structure i s subsequently used to  calculate i n t e n s i t i e s which are then compared with the observed intensities.  Usually, the structure i s deemed s a t i s f a c t o r y only when  the average percent  d i f f e r e n c e between the observed and calculated  i n t e n s i t i e s , the R f a c t o r , f a l l s below 10%.  Otherwise, the structure  i s successively r e f i n e d using a least-squares refinement method u n t i l the R factor i s minimal and s a t i s f a c t o r y . A l l computations involved i n X-ray structure determinations are c a r r i e d out using a d i g i t a l computer. Thus used, t h i s method y i e l d s the structure, conformation, stereochemistry,  intramolecular bond distances, the packing arrangement i n  the c r y s t a l as w e l l as the intermolecular geometries and distances. The next step i n e s t a b l i s h i n g s t r u c t u r e - r e a c t i v i t y c o r r e l a t i o n s i s to study the reactions or the lack thereof of the c r y s t a l l i n e compound. Since, a l l r e a l c r y s t a l s contain imperfections  and since defects  i n c r y s t a l s have been shown to play an important r o l e i n chemical 2 r e a c t i v i t y , a b r i e f discussion of these defects i s desirable. 2—16 Defects i n Crystals and Their E f f e c t s on Chemical R e a c t i v i t y Imperfections  i n non-metallic  s o l i d s , of which organic s o l i d s  are an example, are complex and diverse and have not been as systematically and thoroughly studied as those found i n metals.  Furthermore, the study  -  A  -  of c r y s t a l defects has been the s p e c i a l t y of' s o l i d state p h y s i c i s t s . r e s u l t has been a mathematical and highly t e c h n i c a l treatment of subject.  Only a q u a l i t a t i v e and  s i m p l i s t i c discussion  The  the  of c r y s t a l  defects w i l l be attempted i n t h i s text. Possible defects i n s o l i d s can be c l a s s i f i e d into four A.  Zero-dimensional or point defects e.g.  ooooooo ooooooo ooo ooo ooooooo ooooooo  vacancies and  interstitials.  ooo ooo ooo ooo ooooooo o o o^o o o ooo ooo  (a) Figure 1.  categories;  (b)  (a) Vacancy; (b) I n t e r s t i t i a l atom  A vacancy i s formed by the absence of an atom from an atomic s i t e while an i n t e r s t i t i a l i s what r e s u l t s when an atom i s present at a non-atomic site. B.  These two defects are i l l u s t r a t e d i n Figure  1.  One-dimensional or l i n e defects commonly referred to as  dislocations.  A d i s l o c a t i o n i s a boundary between two  parts of a c r y s t a l which are  displaced with respect to one  There are two  another.  viz.,edge and screw d i s l o c a t i o n s .  The  types of  dislocations  f i r s t type i s exemplified i n  Figure 2b i n which an extra h a l f plane of atoms has been inserted  into  the top half of the c r y s t a l l a t t i c e giving r i s e to a severe d i s t o r t i o n of the atomic layers i n the vicinity"'of the d i s l o c a t i o n . d i s l o c a t i o n may  begin and  An edge  end anywhere i n the c r y s t a l and so may  not  < a  >  F i g u r e 2.  (b)  Model o f a s i m p l e c u b i c l a t t i c e ; (a) t h e p e r f e c t c r y s t a l , (b) a view o f an edge d i s l o c a t i o n caused by t h e i n s e r t i o n o f an e x t r a h a l f p l a n e o f atoms, ABCD.  always be p e r c e p t i b l e  externally.  A screw d i s l o c a t i o n ,  hand, m a n i f e s t s i t s e l f on the c r y s t a l s u r f a c e . dislocation  F i g u r e 2.  on the o t h e r  F i g u r e 2c i l l u s t r a t e s a screw  caused by the d i s p l a c e m e n t o f t h e two f a c e s o f the ABCD p l a n e  (c) a screw d i s l o c a t i o n ; (d) growth s p i r a l on t h e f a c e o f an n - p a r a f f i n (C36H74) c r y s t a l r e s u l t i n g from a screw d i s l o c a t i o n (reproduced from r e f e r e n c e 6 ) .  - 6 -  i n the d i r e c t i o n s shown.  When such a s l i p occurs during c r y s t a l l i z a t i o n ,  i t usually gives r i s e to a growth s p i r a l which i s not uncommon i n long chain hydrocarbons grown from solution by cooling.  Figure '2d i s a  photograph of one such c r y s t a l reproduced from reference C.  Two  dimensional  6.  or surface defects include boundary d i s l o c a t i o n s of  one kind or another.  We  s h a l l concern ourselves with three kinds of  boundary imperfections, viz., defects of surface atoms, phase boundary d i s l o c a t i o n s and g r a i n boundary d i s l o c a t i o n s .  The atoms i n a s i n g l e  c r y s t a l are held together by a cohesive force which may i o n i c , covalent, or van der Waals type.  be of the m e t a l l i c ,  Regardless of which type of  cohesive force i s involved, the atoms on the surface of the c r y s t a l experience  only a f r a c t i o n of the t o t a l force f e l t by the atoms i n the  i n t e r i o r of the c r y s t a l .  This, plus the fact that they are exposed to  an environment d i f f e r e n t from the environment of t h e i r i n t e r i o r  counter-  parts, makes surface atoms d i f f e r e n t from those of the bulk c r y s t a l . They are usually d i s t o r t e d and have properties unlike those of the bulk c r y s t a l . may  This deviation i s c l a s s i f i e d as a defect inasmuch as i t  be the i n i t i a t o r or i n h i b i t o r of a p h y s i c a l or chemical process.  second type of boundary defect i s caused by the presence of one or more phases within the c r y s t a l e.g. the presence of an impurity or the formation of product(s) may inside of the c r y s t a l . serve as a d e f e c t  give r i s e to new  The reactant-product  site.  phases on the surface or i n t e r f a c e may  L a s t l y , grain boundaries may  then . act as defect  The  - 7 -  sites.  Most s o l i d s c r y s t a l l i z e out, not as s i n g l e c r y s t a l s , but as  aggregates of c r y s t a l s .  Any two grains represent  two single c r y s t a l s  and a misorientation between them constitutes a grain boundary d i s l o c a t i o n . The atoms at such s i t e s are d i s t o r t e d .  In a d d i t i o n , such locations  are the s i t e s of other defects such as i n t e r s t i t i a l s and holes. D.  Three-dimensional or volume defects r e f e r to voids and i n c l u s i o n s .  In the perfect l a t t i c e , a l l atoms are i n minimum energy positions and only v i b r a t i o n a l motion about these positions occurs.  When the atoms  are displaced from t h e i r minimum energy p o s i t i o n s , as i s the case at the s i t e of d i s l o c a t i o n s , then the atoms are subjected to forces that tend to move them back to t h e i r equilibrium p o s i t i o n s .  The movement of  atoms i n the v i c i n i t y of the d i s l o c a t i o n to correct the defect often r e s u l t s i n the formation of c l u s t e r s of vacancies or voids.  These  channels of empty space and vacancies, i n general, provide a mechanism of diffusion i n solids.  Figure 3 i s a diagramatic  movement i n the l a t t i c e f a c i l i t a t e d by a void. i l l u s t r a t i o n , the departure  of the designated  representation of As can be seen from this  atom from an atomic s i t e  to the s i t e of the void leaves behind a vacancy.  This mechanism of  d i f f u s i o n , therefore, r e s u l t s i n the creation of a new defect s i t e .  The  m u l t i p l i c a t i o n of defect s i t e s , i n this fashion, can be an e f f e c t i v e method of propagating  reactions permissible only at defect s i t e s .  A second  example of volume defect i s the presence of impurities or i n c l u s i o n s , i n general.  An i n c l u s i o n i n the c r y s t a l l a t t i c e can be an impurity, an  entrapped molecule of the solvent of c r y s t a l l i z a t i o n or i n the case of  - 8 -  ooooooooo ooooooooo ooooooooo oo# ooo ooooooooo ooooooooo ooooooooo  ooooooooo (b)  (a) Figure 3.  (a) a void formed from a c l u s t e r of vacancies; (b) the d i f f u s i o n of an atom ( © ) to a new atomic s i t e and the creation of a vacancy at the o r i g i n a l atomic s i t e .  s o l i d state reactions, a product molecule.  There are two major e f f e c t s  of these inclusions namely ( i ) they, generally, lower the melting point of the host and ( i i ) they may i n i t i a t e or terminate a physical and/or chemical process within the c r y s t a l . For s i m p l i c i t y i n i l l u s t r a t i o n s , only monatomic molecules have so f a r been used i n defining s t r u c t u r a l f a u l t s .  Although, a l l  pf the above discussion applies equally w e l l to polyatomic molecules such as organic s o l i d s , the sheer bulk and complexity of these molecules give r i s e to other considerations which w i l l now be discussed. One of the major differences between s o l i d s of small molecules such as metals and those of large organic e n t i t i e s i s the rate of d i f f u s i o n through the s o l i d .  As mentioned  e a r l i e r , one mechanism of  d i f f u s i o n i n s o l i d s e n t a i l s the movement of an atom from an atomic s i t e to an empty space (a void or vacancy).  The energy required to move a  - 9 -  s m a l l atom o r i o n f r o m one  l o c a t i o n t o a n o t h e r i s q u i t e s m a l l compared  t o t h a t n e c e s s a r y t o e f f e c t the movement o f a complex m o l e c u l e such as an o r g a n i c one.  The  c a l c u l a t e d c o e f f i c i e n t of d i f f u s i o n i n a s i n g l e  c r y s t a l of a n t h r a c e n e i t s m e l t i n g p o i n t and  i s of the o r d e r o f 10 ^  cm^sec ^ a t 40°  the a c t i v a t i o n energy f o r d i f f u s i o n  t o be 42 k c a l per mole .  below  i s calculated  D i f f u s i o n i n o r g a n i c s o l i d s can t h e r e f o r e  assumed t o be n e g l i g i b l e .  One  m a n i f e s t a t i o n o f t h i s , i s the  be  inability  o f r a d i c a l s formed d u r i n g d e c o m p o s i t i o n o f o r g a n i c c r y s t a l s t o combine to products,  a phenomenon termed a cage e f f e c t ^ ' ^ .  Not  o n l y a r e mole-  c u l e s c o n f i n e d t o t h e same l o c a t i o n i n a c r y s t a l b u t o t h e r m o t i o n s such as t u m b l i n g  seem t o be a b s e n t as w e l l .  molecular  P r o o f of  comes f r o m t h e p e r s i s t e n c e , o v e r p e r i o d s up t o months, of the  this anisotropy  ( e l e c t r o n s p i n - n u c l e a r s p i n m a g n e t i c i n t e r a c t i o n ) e x e m p l i f i e d by h y p e r f i n e s p l i t t i n g s i n the e l e c t r o n s p i n r e s o n a n c e s p e c t r a of  proton  various  6 8 o r g a n i c compounds w h i c h have been exposed t o i o n i z i n g r a d i a t i o n ' . R e s t r i c t i o n s such as t h i s on m o l e c u l a r  movements form the b a s i s of  t o p o c h e m i c a l p o s t u l a t e w h i c h w i l l be d i s c u s s e d  later.  A second f e a t u r e of complex m o l e c u l e s s u c h as  organic  compounds i s t h e i r p o t e n t i a l t o c r y s t a l l i z e put. i n more t h a n one form.  P o l y m o r p h i s m may  polymorphic,  be a s s o c i a t e d w i t h v a r i a t i o n s i n c o n f o r m a t i o n  the m o l e c u l e s and/or w i t h . t h e crystal lattice.  the  packing  arrangement o f m o l e c u l e s i n the  Polymorphs of the same s u b s t a n c e d i f f e r n o t o n l y i n  t h e i r p h y s i c a l p r o p e r t i e s but may  react d i f f e r e n t l y .  Although, t h i s  m u l t i p l i c i t y o f form i s not a d e f e c t as s u c h , t h e c o n t a m i n a t i o n  of  one  of  - 10 -  c r y s t a l form by the presence of a second form i s undesirable i n the study of such s o l i d s .  There are two types of polymorphism namely enantio-  tropic and monotropic.  When each of two polymorphs  i s stable at a  given temperature range and pressure, then the two are said to be enantiotropic.  This means that a substance A w i l l e x i s t i n polymorphic  modification A^ at T° and a pressure of P^.  At T° and T^, i t i s  transformed i n t o polymorphic modification k^.  In the second type of  polymorphism, one of the p a i r i s unstable at a l l temperatures below the melting point.  Such a p a i r i s said to be monotropic.  This l a t t e r  form of polymorphism presents less problem i n organic reactions than the former since the metastable form can only be prepared by quenching the melt and i s , therefore, u n l i k e l y to form during c r y s t a l l i z a t i o n or reaction.  Enantiotropic forms, on the otherhand, may i n t e r f e r e i n  reactions i n the following manner: ( i ) where one form interconverts to the other during the course of a reaction, i t becomes d i f f i c u l t to determine from which modification the reaction i s occurring.  One such  compound i s cis-decahydronaphthalene which undergoes enantiotropic change at about 14° below i t s melting point"*"^; ( i i ) when a reaction sample containing predominantly one polymorph i s contaminated by a second polymorph.  Although, i t i s possible to check s i n g l e c r y s t a l s  grown f o r X-ray c r y s t a l l o g r a p h i c purposes, the s e n s i t i v i t y of this method i s only about 5%.  Furthermore, checking bulk samples used  i n organic s o l i d state reactions i s impractical.  Fortunately, this type  of contamination can be treated much l i k e defects. Since there are :  very few of the unwanted forms as compared to the bulk of the c r y s t a l s ,  - l i -  the properties and r e a c t i v i t y of the. c r y s t a l w i l l approach that.of _. _  the pure form. As mentioned e a r l i e r , organic s o l i d s are generally lower melting and more prone to contamination than the inorganic ones.  One  consequence of t h i s i s that, unless reaction temperatures are chosen so as to be many degrees below the melting point, an apparent solid-phase reaction may  a c t u a l l y be occurring i n a molten region of the c r y s t a l .  Moreover, as reaction proceeds, product molecules w i l l further depress the melting point of the host sample so that not only should reaction temperatures be below the melting point of the s t a r t i n g m a t e r i a l but must be below the e u t e c t i c temperature of the mixture reactant and  comprising  product(s).  We have so f a r defined some of the possible defects which can be present i n a c r y s t a l l i n e s o l i d .  Experimentally,  often implicated i n organic s o l i d reactions are kind or another.  the defects most  d i s l o c a t i o n s of  one  To understand t h e i r r o l e i n such reactions, an examination  of the stages involved i n transforming  reactant molecules to product  within the c r y s t a l l a t t i c e of the reactant w i l l be u s e f u l .  To be pertinent,  the discussion w i l l be l i m i t e d to photochemical transformations  i n the  s o l i d state. Let R denote a reactant molecule i n the c r y s t a l l a t t i c e . Following the absorption of l i g h t by R, i t i s promoted to the  first  1 * excited s i n g l e t s t a t e ,  R .  I t may  then (a) react to give product, P, or  (b) deactivate ( i ) r a d i a t i v e l y (fluoresce) or ( i i ) . non-radiatively to the  - 12 -  ground state, or (c) intersystem-cross into the excited t r i p l e t manifold, R , from which i t can ( i ) react, ( i i ) transfer i t s e x c i t a t i o n energy to a second molecule,  ( i i i ) deactivate r a d i a t i v e l y (phosphoresce) or  non-radiatively to the ground state or (d) t r a n s f e r i t s e x c i t a t i o n energy to another molecule R".  This e n t i r e sequence of events, schematically  represented i n Scheme 1, i s c r y s t a l structure dependent.  The only processes  which may d i r e c t l y or eventually lead to"product formation are (a) and (d)  Scheme 1 p.  R  from the excited s i n g l e t manifold and (c) ( i ) and ( i i ) from the excited t r i p l e t state. of  Attention w i l l , therefore, be focused on the e f f e c t s  s t r u c t u r a l imperfections on these processes.  In a reaction i n which  the absorption of energy leads d i r e c t l y to r e a c t i o n i . e . energy transfer does not occur, molecules  situated at or near l a t t i c e defects play no  s i g n i f i c a n t r o l e since t h e i r concentration i s n e g l i g i b l e compared to the concentration of molecules i n ordered arrays.  The photodimerization  11 12 of trans-cinnamic a c i d and i t s d e r i v a t i v e s ' affords an example of t h i s  - 13 -  type of r e a c t i o n .  In one such r e a c t i o n , Cohen and coworkers^  irradiated  mixed c r y s t a l s of p-methoxycinnamic acid and p-methylcinnamic acid with both f i l t e r e d and u n f i l t e r e d l i g h t .  With f i l t e r e d l i g h t , only p-methoxy-  cinnamic acid monomers absorbed the l i g h t .  Analyses of the r e s u l t i n g  products showed them to be the homodimer formed by the combination of an excited p-methoxycinnamic acid with a non-excited p-methoxycinnamic acid together with the heterodimer formed by the reaction of excited p-methoxycinnamic acid with a non-excited p-methylcinnamic  acid.  Hardly any homodimer of p-methylcinnamic acid was formed.  When u n f i l t e r e d  l i g h t was used, however, the products comprised both homodimers and also the heterodimer.  These r e s u l t s , summarised i n Scheme 2 below, show that  only molecules which i n i t i a l l y absorb the i r r a d i a t i o n react i . e . no 12  energy transfer occurs i n t h i s system.  Scheme For f i l t2 e r e d l i g h t hv  A  A A  ic  + A  A* + B  ^  »* A > A  Schmidt and coworkers  For u n f i l t e r e d l i g h t hv  A  A 2  > AB  have  A  ic  > A  + A —>  A* + B  * A  hv  B ic  2  » AB  B  + B —>  the c r y s t a l structures  and dimerization  reactions  * B  2  B* + A —> AB  A = p-methoxycinnamic a c i d ; B = p-methylcinnamic  studied  > B  acid  of these and  other cinnamic acids and i n a l l cases found only the products  predicted  - 14 -  from the o r i e n t a t i o n of the monomers i n the c r y s t a l l a t t i c e .  Thus, the  a-type c r y s t a l (Scheme 3. below) i n which monomer p a i r s are related by a centre of symmetry give the centrosymmetric dimer.  The second type  of c r y s t a l , the 3-type, i n which monomer p a i r s are r e l a t e d by simple t r a n s l a t i o n along a c r y s t a l l o g r a p h i c axis dimerize to the mirrorsymmetric dimer.  And l a s t l y , the y-type c r y s t a l i n which the double bonds of  adjacent monomers are o f f s e t i n such a way  that they do not overlap and  Scheme 3 A r — — — B m \mu  -  x  — ~ — A r  edge-on view of carboxylic acid p a i r  X = centre of symmetry  COOH  o  a-type.  Separation of double bonds - 4A  COOH  hv ' Ar  B-type.  —  =z-^mm—x.  -=—:Ar  X:OOH  Separation of double bonds - 3.8-4.1A Ar  Ar——-,  i I  -=—Ar —Ar  Ar  hv  COOH  00H  I  Y-type.  Separation of double bonds - 4.8-5.2A  Ar—=r—• Ar—=-  — : — Ar •—=—Ar  hv  ->  No Reaction  - 15 -  o  the distance between them i s 4.8A or greater are found to be photochemically i n e r t . topochemically  In contrast to these photodimerizations  which are  c o n t r o l l e d , there are s o l i d state reactions which are  best understood i n terms of the geometry of molecules situated at or near defective s i t e s such as d i s l o c a t i o n s .  The opportunity  f o r molecules  at d i s l o c a t i o n s to c o n t r o l r e a c t i v i t y arises when s t e r i c or other factors make reaction i n the.perfect parts of the c r y s t a l e n e r g e t i c a l l y unfavorable and that at d i s l o c a t i o n s comparatively  desirable and a mechanism exists  for e x c i t a t i o n energy to reach such defective s i t e s .  An example of t h i s  i s provided by the photodimerization  anthracenes i n  the'solid s t a t e ^ " ^ ' ^ . forms, a, g and y.  of 9-substituted  As i n the cinnamic acids, there are three c r y s t a l  The a type i s predicted on the basis of the monomer  arrangements i n the c r y s t a l to give the centrosymmetric dimer and i t does, Scheme 4 ; the Y-type i s photoinert as expected but the g-type which on the basis of the c r y s t a l structure should give the mirrorsymmetric dimer reacts to give the centrosymmetric dimer.  The formation  topochemical dimer i s now f a i r l y w e l l understood.  of this non-  Dimerization here  involves bonding the C9, CIO p o s i t i o n s of one monomer to the CIO, C9  Scheme 4  arrangement  - 16 -  g-type  m i r r o r s y m m e t r i c dimer, n o t formed  centrosymmetric dimer, formed  Y-type  No  Reaction  - 17 -  p o s i t i o n s , .respectively, of i t s nearest  neighbour.  When any o f t h e s e  p o s i t i o n s i s s u b s t i t u t e d , t h e 3-arrangement becomes e n e r g e t i c a l l y u n f a v o u r a b l e f o r d i m e r i z a t i o n presumably because o f s t e r i c  hindrance.  So t h a t one w o u l d e x p e c t such c r y s t a l s t o be p h o t o i n e r t .  T h i s i s found  t r u e f o r some o f t h e 9 - s u b s t i t u t e d  anthracenes"^"^  But  i n others  and 9 , 1 0 - d i s u b s t i t u t e d  l i n e a r d e f e c t s i . e . d i s l o c a t i o n s have made p o s s i b l e t h e  h e a d - t o - t a i l a p p r o a c h o f two monomers s o t h a t r e a c t i o n b e g i n s o n l y a t t h e s e d e f e c t i v e s i t e s and i s p r o p a g a t e d t h r o u g h m u l t i p l i c a t i o n o f t h e d e f e c t as r e a c t i o n p r o c e e d s . has  I n these anthracene-derived  a l s o been shown t h a t t h e i n i t i a l a b s o r p t i o n  compounds, i t  o f i r r a d i a t i o n need  n o t be by t h e m o l e c u l e s a t t h e s e d e f e c t i v e s i t e s i n o r d e r  t o have t h e  13 r e a c t i o n t o occur.  Both i m p u r i t i e s  and d i s p l a c e d m o l e c u l e s a t d e f e c t i v e  14 sites  have been shown t o a c t as e f f e c t i v e e x c i t o n t r a p s i n a n t h r a c e n e  crystals.  So t h a t e n e r g y absorbed by t h e b u l k o f 9 - s u b s t i t u t e d a n t h r a c e n e  c r y s t a l s i s p a s s e d on f r o m one p a i r o f m o l e c u l e s t o t h e n e x t u n t i l i t r e a c h e s a d e f e c t i v e s i t e where monomer p a i r arrangements f a v o r The  formation  reaction.  o f t h e u n e x p e c t e d dimer i n such c a s e s i s , t h e r e f o r e , n o t  a v i o l a t i o n of the topochemical postulate since the r e a c t i o n i s not occurring w i t h i n the " p e r f e c t " regions due  of the c r y s t a l l a t t i c e but i s  t o f a v o r a b l e r e a c t i o n c o n d i t i o n s a t d i s l o c a t i o n s i n t h e c r y s t a l as  s u g g e s t e d and shown by Thomas and Williams^""*. 17-21 Energy T r a n s f e r i n O r g a n i c S o l i d s : I t w i l l be u s e f u l t o d e f i n e t h e term " e x c i t o n " as i t i s used i n the p h o t o c h e m i c a l l i t e r a t u r e on o r g a n i c s o l i d s .  In solids, excitation  - 18 -  energy a b s o r b e d by a chromophore i n a m o l e c u l e may be i m m e d i a t e l y passed on t o a n e i g h b o r i n g m o l e c u l e i n t h e same c r y s t a l .  Thus, t h e  e x c i t a t i o n energy c a n be thought o f as b e i n g s h a r e d between t h e m o l e c u l e s w i t h i n that p a r t i c u l a r c r y s t a l . i s termed an e x c i t o n .  This delocalized e x c i t a t i o n  energy  The m i g r a t i o n o f an e x c i t o n from m o l e c u l e t o 18  m o l e c u l e w h i c h has been v a r i o u s l y d e s c r i b e d as t u n n e l l i n g j u m p ^ and a r a n d o m - w a l k " ^ ' ^  19 , a hop  , a  by d i f f e r e n t i n v e s t i g a t o r s o c c u r s t h r o u g h l o n g  3  range i n t e r a c t i o n between t r a p s i n c o n t r a s t t o t h e mechanism o f t r i p l e t t r i p l e t energy t r a n s f e r i n s o l u t i o n w h i c h o c c u r s l a r g e l y t h r o u g h m o l e c u l a r collisions.  As mentioned  e a r l i e r , energy t r a n s f e r o c c u r s i n some systems  and n o t i n o t h e r s depending  on t h e t y p e s and magnitude o f t h e i n t e r a c t i o n  between t h e donor and r e c i p i e n t m o l e c u l e s . p r o b a b i l i t y o f t r a n s f e r i s l a r g e (>10^  I n c a s e s where t h e  s e c "*") i t i s e s t i m a t e d t h a t t h e  jump t i m e , T, f o r a m i g r a t i n g e x c i t o n can be as s h o r t as o r s h o r t e r 91 -13 t h a n l a t t i c e r e l a x a t i o n times^- - (10 s e c ) so t h a t i n t h e s e cases t h e 1  * e x c i t e d s t a t e molecule S S  Q  and i t s s u r r o u n d i n g u n e x c i t e d m o l e c u l e s  h a v e t h e same geometry.~ . T h i s keeps t h e p r o b a b i l i t y o f t r a n s f e r  h i g h and promotes e x t e n s i v e e x c i t o n m i g r a t i o n . When, on t h e o t h e r hand, l a t t i c e r e l a x a t i o n precedes t h e t r a n s f e r , c o n s i d e r a b l e energy i s expended t h e r m a l l y and e x c i t o n m i g r a t i o n i s c u r t a i l e d .  Examples o f  s o l i d systems w h i c h have been shown t o e x h i b i t s u b s t a n t i a l e x c i t o n 17 18 20 m i g r a t i o n a r e t h o s e o f benzene , n a p h t h a l e n e , and a n t h r a c e n e S e v e r a l i m p o r t a n t c o n c l u s i o n s can be drawn from t h e s e works:  - 19 -  (i) Since the average number of jumps or transfers i s x/T where x i s the l i f e t i m e of the exciton and T i s the time within which a s i n g l e 20a transfer occurs  , and since a t r i p l e t exciton i s longer-lived than a  s i n g l e t exciton, i t follows that migration of a t r i p l e t exciton through a c r y s t a l i s more extensive  than that of a s i n g l e t exciton.  Nieman and  Robinson'''''' estimated that i n pure organic c r y s t a l s , ^10^" t r i p l e t energy 4 6 migrations  are p o s s i b l e per r a d i a t i v e l i f e t i m e as compared to 10  - 10  for the lowest s i n g l e t . ( i i ) The more extensive wandering of the t r i p l e t increases the p r o b a b i l i t y of i t s a n n i h i l a t i o n at defective s i t e s and also through t r i p l e t - t r i p l e t quenching.  This i s borne out by the fact that many  organic c r y s t a l s having long-lived t r i p l e t states do not phosphoresce. ( i i i ) S t r u c t u r a l f a u l t s and/or chemical impurities can act as exciton traps to terminate the t r a n s f e r process.  These energy sinks  may then become the s i t e s of p h y s i c a l processes such as phosphorescence and/or the reaction centres within the c r y s t a l . 2. Photochemistry of Tetrahydro-1,4-naphthoquinone and I t s Derivatives 22 Diels and Alder  reported  the formation  of a polymeric  material of unknown molecular weight when they exposed c r y s t a l s of the parent compound, 4a,5,8,8a-tetrahydro-l,4-naphthoquinone, 3_, to sunlight. 23 Over three decades l a t e r , Cookson and coworkers and s i m i l a r reactions.  reinvestigated t h i s  In both ethyl acetate s o l u t i o n and as c r y s t a l l i n e  material, UV i r r a d i a t i o n through Pyrex of compound 3. was reported to  - 20  give mainly t a r .  -  Although, t h e i r attempts at c h a r a c t e r i s a t i o n  w i t h l i t t l e s u c c e s s , they t e n t a t i v e l y a s s i g n e d i t the d i m e r i c I I , o f unknown s t e r e o c h e m i s t r y , (eq.  met structure,  1).  hu  eq.  24 More r e c e n t l y , S c h e f f e r irradiation, t r i c y c l i c and  (X > 340  and  nm)  coworkers  o f 3. and  have shown t h a t s e l e c t i v e  i t s d e r i v a t i v e s i n s o l u t i o n gave  t e t r a c y c l i c p r o d u c t s i n moderate t o q u a n t i t a t i v e y i e l d s .  T h e i r r e s u l t s are summarized i n Scheme 5 . 25 r e c e n t l y appeared i n the l i t e r a t u r e  and  The  t y p e 8 p r o c e s s has  formally  involves  o f a h y d r o g e n v i a a five-membered t r a n s i t i o n s t a t e .  On  the  only  abstraction  the o t h e r hand,  the a b s t r a c t i o n of a Y h y d r o g e n by a c a r b o n y l oxygen t h r o u g h a s i x -  membered c y c l i c t r a n s i t i o n s t a t e i s commonplace 26 r e f e r r e d t o as the N o r r i s h Type I I p r o c e s s  .  and The  has  been w i d e l y  third reaction  type,  c denoted as y t o d i f f e r e n t i a t e i t from the p r e v i o u s Y - p r o c e s s i n v o l v e s the a b s t r a c t i o n of a Y h y d r o g e n by c a r b o n 2 of t h e ene-dione system. This p r o c e s s i s analogous t o t h a t r e p o r t e d i n the p h o t o c h e m i s t r y of some 27 -  s u b s t i t u t e d c y c l o p e n t e n o n e s and type i . e . , i n t r a m o l e c u l a r  cyclohexenones  .  The  fourth  o x e t a n e f o r m a t i o n , i s f o r m a l l y a 2+2  reaction cycloaddition  o f a c a r b o n y l group t o an o l e f i n i c d o u b l e bond. Such a r e a c t i o n i s w e l l 28 documented i n the l i t e r a t u r e . The l a s t r e a c t i o n t y p e l e a d i n g to a caged  - 21 -  - 22 -  - 23 -  structure (Scheme  5 ) i s also an intramolecular  2+2 cycloaddition.  This time, however, the addition i s between the two o l e f i n i c double 29 bonds.  This reaction i s also not without precedent  .  There are two  simple mechanisms which can explain the formation of the various products a r i s i n g from hydrogen abstraction. mechanism shown i n Scheme . 5  One of these i s the b i r a d i c a l  and the other i s the charge-transfer  pair mechanism shown i n Scheme 6 .  or ion  The l a t t e r mechanism involves the  Scheme 6 Type 6  etc.  - 25 -  H  ••etc-  t ransfer  t r a n s f e r of an electron from the o l e f i n i c ir system to the excited enedione chromophore followed by the abstraction of a proton by the oxygen. E l e c t r o n reorganization i n the r e s u l t i n g d i p o l a r intermediate would then give r i s e to the same b i r a d i c a l intermediate formed from the d i r e c t abstraction of a hydrogen atom by the oxygen.  The b i r a d i c a l pathway  follows from that generally accepted f o r the Norrish Type I I and related processes.  On the other hand, charge transfer bands have been detected  i n the UV absorption spectra of some p-benzoquinone d e r i v a t i v e s similar 24 to those studied by Scheffer and coworkers  .  For example, compound IV  (Table 1) has an absorption at 307 nm with a higher e x t i n c t i o n Table 1  UV absorptions,  X  n m  (e) TH-TT*  (allowed)  charge-transfer  255(15,500)  Tr->-rr*  (forbidden)  n->-rr*  355(800)  435(26)  385(520)  448(50)  III  257(14,500)  IV :  307(260)  - 26 -  c o e f f i c i e n t than i t s n,ir* absorption.  There was no corresponding  absorption i n the 300-350 nm region, however, f o r compound I I I .  Cookson  30 and coworkers  ascribed the 307 nm absorption to a charge-transfer  state a r i s i n g from overlap of the remote double bond with the carbonyl of the p-benzoquinone chromophore.  This i s not unreasonable since  p-quinones are good electron acceptors and may accept an electron from the remote double bond i f the geometry of the molecule allows f o r overlap of the two chromophores.  So that, although the b i r a d i c a l  mechanism accounts f o r the products observed i n the investigations of 24 Scheffer and coworkers  , the p o s s i b i l i t y of a charge-transfer mechanism  needs to be explored. B i r a d i c a l vs Charge-transfer Mechanisms: Throughout  t h i s discussion i t w i l l be important to bear i n  mind that both of these mechanistic pathways involve a b i r a d i c a l i n t e r mediate.  Such an intermediate i s necessary to explain the d i f f e r e n t  products formed i n these hydrogen abstraction reactions.  So that i n  considering these two pathways, one i s s o l e l y concerned with the step(s) leading to the formation of the b i r a d i c a l . The f i r s t event i n the chain i s surely the absorption of light.  This promotes themolecule from i t s ground state energy l e v e l to  an excited state.  What i s the nature of t h i s excited state?  As w i l l be  shown l a t e r , l i k e the Norrish Type II.reaction, the reactions of these t e t r a hydronaphthoquinones  proceed.from both, the s i n g l e t a n d . t r i p l e t excited states.  - 27  Since d e a c t i v a t i o n from h i g h e r 12 s o l u t i o n ( k - 10 are i n v o l v e d .  13 -10  -  excitation levels i s quite rapid i n  -1 sec  ) , one  assumes t h a t o n l y f i r s t e x c i t e d  I n t h e N o r r i s h r e a c t i o n , I t I s found t h a t i n  acyclic  ketones the p e r c e n t a g e o f s i n g l e t r e a c t i o n depends on the s t r e n g t h yC-H  bond - as the bond becomes w e a k e r , the p r o p o r t i o n 26a  from the s i n g l e t s t a t e i n c r e a s e s high intersystem  .  On  states  of  of r e a c t i o n  the  occurring  t h e . o t h e r hand, k e t o n e s w i t h  c r o s s i n g e f f i c i e n c y e.g.  a r o m a t i c k e t o n e s , may  e x p e c t e d t o r e a c t m o s t l y from t h e i r t r i p l e t s t a t e s .  A second  be question  t o be s e t t l e d about t h e n a t u r e of t h e e x c i t e d s t a t e ( s ) i n v o l v e d i n t h e s e r e a c t i o n s has  t o do w i t h the f a c t t h a t i n some k e t o n e s t h e r e a r e  l o w - l y i n g t r i p l e t s t a t e s namely, n , 7 T * a n d ^ r r . T r * . 3  obtained  two  Triplet lifetimes  from p h o s p h o r e s c e n c e s t u d i e s show t h a t , of the two  triplets,  3 the  n,ir* i s the s h o r t e r l i v e d , i t s l i f e t i m e b e i n g g e n e r a l l y of  o r d e r of 10 ^ t o 10 ^ s e c . ^ ' .  U s i n g t h e s e l i f e t i m e s i t has  3  the  been  e s t a b l i s h e d t h a t k e t o n e s w i t h l o w - l y i n g p u r e n , i r * t r i p l e t s undergo N o r r i 3 h Type I I r e a c t i o n w h i l e are, generally, unreactive.  those w i t h pure I T , I T * lowest  The  r e a c t i v i t i e s of t h e s e two  the  triplets triplets 26b  in intramolecular  h y d r o g e n a b s t r a c t i o n r e a c t i o n s have been e s t i m a t e d  t o d i f f e r by a t l e a s t a f a c t o r o f 10*\  This i s not  surprising, i f ,  as i s g e n e r a l l y assumed, the r e a c t i o n i n v o l v e s t h e a b s t r a c t i o n o f a hydrogen atom by an e l e c t r o n - d e f i c i e n t oxygen.  For the n , T T * s t a t e  a c o n f i g u r a t i o n i n w h i c h an e l e c t r o n d e f i c i e n c y has been c r e a t e d the oxygen due  t o t h e p r o m o t i o n of one  e l e c t r o n s i n t o an a n t i b o n d i n g  has  at  of i t s non-bonding p a i r o f  (ir*) o r b i t a l .  The  n,Tr* e x c i t e d s t a t e  of  - 28 -  carbonyl  compounds, therefore, c l o s e l y resembles and acts l i k e an 26b  alkoxy r a d i c a l  . The  TT,TT*  s t a t e , on the other hand, has an e l e c t r o n -  r i c h rather than an electron d e f i c i e n t oxygen as depicted i n Figure 4 making i t less reactive i n Type I I reactions.  >: = 0 : '  J£>—  ground state  n,Tr*  O  Unfortunately,  some  ^J3.—O:  state  TT,TT*  Figure 4: 3 ketones react v i a excited states which are neither pure thus making the above generalization incomplete. i n t h e i r interpretations of r e s u l t s i n t h i s area.  3 n,TT*  nor  Investigators  Tr,Tr*,  differ  To assume that only  3 n,TT*  states undergo the hydrogen abstraction r e a c t i o n would lead to  the i n e v i t a b l e conclusion that ketones having t h e i r  Tr,Tr*  states below  3 their  n,Tr*  react because (A) there i s v i b r o n i c mixing of the two  states, thus conferring some  n,Tr*  character on the excited state which  reacts or, a l t e r n a t i v e l y , that (B) the with the  n,Tr*  TT,TT*  thermally  equilibrates  and i t i s t h i s l a t t e r t r i p l e t which reacts.  Since  neither of these two p o s s i b i l i t i e s shown i n Scheme 7 seems s a t i s f a c t o r y 31 i n explaining  a l l of the a v a i l a b l e experimental data  , the e a r l i e r  26a view  that either or both mechanisms may operate i n a given ketone  seems the safest i n t e r p r e t a t i o n to date. Whatever the nature of the excited s t a t e i n these reactions, i t i s ultimately t i e d i n with the question  of whether or not the next  - 29 -  Scheme 7  26b,31  TT.Tf* Tf , T f *  n,TT*  Tf , TT*  n,TT  n,Tf* »  \  \  X \  mixed, ^ "mostly n , T r *  n«Tf * T f , TT* \  mixed, mostly ^Tf, Tf*  product(s)  product(s)  Phenyl ketones  Naphthyl or biphenyl ketones  Tf, Tf*  n,TT* n,Tr*  J L L J U T*  V product(s)  - 30  -  e v e n t i n t h e sequence i n v o l v e s the a b s t r a c t i o n o f a hydrogen atom o r the t r a n s f e r o f an e l e c t r o n b e c a u s e , as mentioned e a r l i e r , t h e d e n s i t y a t t h e oxygen d i f f e r s markedly f o r the n,rr* and The  charge-transfer  distribution.  The  (CT)  TT,TT*  electron  states.  s t a t e resembles the TT , I T * s t a t e i n i t s e l e c t r o n  oxygen i s n u c l e o p h i l i c and  s u b s e q u e n t l y can o n l y  r e a c t i v e i n hydrogen a b s t r a c t i o n r e a c t i o n s i f the t r a n s f e r  be  involves  32 a p r o t o n r a t h e r t h a n a hydrogen atom. the s p e c t r a l and benzophenones.  P o r t e r and  Suppan  p h o t o c h e m i c a l b e h a v i o u r of a v a r i e t y of  have s t u d i e d substituted  T h e i r r e s u l t s showed t h a t d e r i v a t i v e s h a v i n g c h a r g e -  t r a n s f e r l o w e s t t r i p l e t s were even l e s s r e a c t i v e i n hydrogen abstraction reactions  than s u b s t r a t e s  h a v i n g p u r e TV , T T * l o w e s t  Thus the o r d e r of r e a c t i v i t y of t h e s e t h r e e e x c i t e d s t a t e s i s TT,TT*  >CT*.  triplets. n,Tr*  T h i s o r d e r r e f l e c t s the o r d e r of e l e c t r o p h i l i c i t y of  oxygen i n t h e s e t h r e e s t a t e s thus s t r o n g l y i m p l y i n g e l e c t r o n d e f i c i e n t oxygen w h i c h a b s t r a c t s  a  >  the  t h a t i t i s an  hydrogen.  T h i s has  recently  been b o r n e out by t h e p h o t o c h e m i c a l b e h a v i o u r of 3 - v i n y l p h e n y l 33 ketones  .  The  i n t e r a c t i o n o f the Y-6.double bond of k e t o n e s V_ and  w i t h the e x c i t e d c a r b o n y l f o r m a t i o n s was  chromophore i n t h e i r p h o t o c h e m i c a l t r a n s -  e v i d e n c e d by  the i s o m e r i z a t i o n about the double bond i n V I .  Comparison o f t h e i r UV s p e c t r a w i t h t h a t o f v a l e r o p h e n o n e showed t h a t  V  VI  VI  VII  the  - 31 -  i n t e r a c t i o n i s not a ground state phenomenon.  Since ketones have t r i p l e t  energies which f a l l below those of o l e f i n s , an energy transfer which excites the o l e f i n partner i n a Franck-Condon fashion has thermic.  to be endo-  Such endothermic energy transfers are now believed to involve 33 34  charge transfer (CT) complexes  '  . In V where the p o t e n t i a l e x i s t s  for y-hydrogen abstraction, i t was found that i t competed poorly with t r i p l e t decay v i a intramolecular  quenching by the double bond. The  l a t t e r process was favored 100:1  over abstraction.  Furthermore, the  t o t a l quantum y i e l d of Type I I products from compound V was only 1% of the value reported was  clearly  n,Tf*.  f o r compound VII for which the r e a c t i v e state  These r e s u l t s would seem to indicate that the  abstraction of a y-hydrogen v i a a charge-transfer  excited state occurs  very i n e f f i c i e n t l y , i f at a l l . One  example where a charge-transfer  mechanism has been suggested  i s the photochemical hydrogen abstraction process i n small r i n g nitrogen heterocycles transformation,  studied by Padwa and coworkers^"* '* . The 3  3  an example of which i s given i n equation 2, was found  to have, generally, low quantum y i e l d (f0.02) i n s p i t e of the fact that the  n,Tf*  t r i p l e t responsible f o r the transformation  be quenched e f f i c i e n t l y .  The usual explanation  was too reactive to  f o r such low quantum  y i e l d s i n c e r t a i n hydrogen abstraction reactions has been the back  eq. (2) tert-Bu  - 32 -  transfer of the abstracted hydrogen.  The k i n e t i c data on this  particular  system, however, showed that the a b s t r a c t i o n of the hydrogen was irreversible.  A charge-transfer mechanism (Scheme  the authors^"* k a,  8) as proposed by  provides an explanation which i s consistent with both  the low quantum e f f i c i e n c y  and the high t r i p l e t r e a c t i v i t y .  R =tert-Bu  The donation  - 33 -  of an electron by the heteroatom i s thought to occur at a rate  which  exceeds d i f f u s i o n - c o n t r o l l e d rates thus making the t r i p l e t unquenchable. The low quantum e f f i c i e n c y for product formation i s explained by competitive back-transfer of the electron i n the r a d i c a l ion p a i r accompanied by deactivation to the o r i g i n a l ketone.  This mechanism  i n which hydrogen abstraction involves electron t r a n s f e r followed by proton t r a n s f e r has, so f a r , been convincingly demonstrated only i n amino systems.  For example, photoreduction of carbonyl compounds by  amines are w e l l documented and have been shown i n a few cases to involve a charge-transfer (CT) complex formed by the i n t e r a c t i o n of the electron 35 donor with the acceptor  .  In some cases, such complexes have been  detected by t h e i r emission spectra and/or by t h e i r e.s.r. spectra. Nevertheless, the fact that the oxygen analog of amine VIII i . e . compound 9  IX reacts by a d i f f e r e n t mechanism  (Scheme 9) should caution against the  extension of t h i s mechanism to other related systems.  Since the CT  Scheme ,9  IX  mechanism r e l i e s on both the a v a i l a b i l i t y of electrons on the donor atom or group and the ease of reducing the acceptor, both the i o n i z a t i o n  - 34 -  p o t e n t i a l (IP) and the nature of the excited carbonyl chromophore w i l l determine whether or not t h i s mechanism i s f e a s i b l e i n any given system. Thus, the d i f f e r e n c e i n the behaviour of substrates VIII and IX, f o r example, i s l i k e l y due to the higher IP of the non-bonding  electrons  on oxygen r e l a t i v e to those on nitrogen as Padwa and Eisenhardt have 2 5b suggested  .  In the tetrahydro-1,4-naphthoquinone s e r i e s , the p o s s i -  b i l i t y e x i s t s f o r a CT complex formation preceding a b i r a d i c a l i n t e r mediate since cyclohexene and i t s methyl substituted derivatives have IP's 36 ranging from 8.3 to 8.9 eV which are comparable to the reported IP 37 values f o r some primary and secondary a l i p h a t i c amines  which are known  to photoreduce carbonyl compounds by a CT mechanism. C h a r a c t e r i s t i c s of the 8- and y-Hydrogen Abstraction Reactions i n the Tetrahydro-1,4-riaphthoquinone Series: Substituent E f f e c t s There are two e f f e c t s caused by s u b s t i t u t i o n : (i) i n two substrates where both the ene-dione double bond and the c bridgehead p o s i t i o n s bear methyl groups, both g- and y -hydrogen abstraction products were i s o l a t e d , the l a t t e r process being-absent i n a l l other substrates so f a r studied.  The abstraction of a hydrogen by  enone carbon has been reported i n the l i t e r a t u r e as r e s u l t i n g from a 3 TTjir*  27 38 state  '  .  This leads one to conclude that i n the tetrahydro-  naphthoquinone s e r i e s , only when both the bridgehead positions and the ene-dione double bond are substituted with a l k y l groups does the TT ,TT*  -  35  -  t r i p l e t energy l e v e l become s u f f i c i e n t l y lowered to favor reaction from it.  This i s a tenable supposition i n the l i g h t of the findings of 39  other workers  that a l k y l s u b s t i t u t i o n on an enone double bond causes 3  a lowering of the  (Tr,Tr*)  energy l e v e l  ( i i ) the second e f f e c t caused by s u b s t i t u t i o n seems to involve the modes of closure of the intermediate b i r a d i c a l i n the 3-hydrogen abstraction reactions.  As shown i n the generalized scheme (Scheme 10)  f o r such a process, there are four modes of closure open to such a Scheme 10  XIII  XIV  - 36 -  biradical.  The formation of a strained cyclopropane r i n g i n a t r i c y c l i c  structure i s on s t e r i c grounds alone unfavorable and so the complete absence of product type XII i n the s e r i e s i s understandable.  Product  XIII. formed by bonding C - l to C-6 i s formed by a l l substrates except the parent compound i . e . R=R'=R"=H.  In some cases, i t i s the exclusive 24  product from a $-hydrogen abstraction process.  Scheffer and coworkers  have explained the product types encountered i n t h i s series by proposing that the reactions are conformationally c o n t r o l l e d . the assumption  In this proposal,  i s made that these tetrahydro-1,4-naphthoquinones  exist  i n s o l u t i o n mainly i n the twist conformation A, Scheme 11, and that the Scheme 11  XV  mi  d i r a d i c a l intermediate XI, when formed at f i r s t has this same conformation.  From t h i s conformation,  i s between carbons 1 and 6.  the only f e a s i b l e form of r i n g closure  The other p o s s i b l e bonding centres are  either too f a r apart or would lead to the s t e r i c a l l y unfavored cyclopropyl derivative.  Thus, b i r a d i c a l intermediates which are immobilised, say, by  bulky bridgehead XIII.  substituents collapse only to enone-alcohol  product  On the other hand, b i r a d i c a l s which are not r e s t r i c t e d to this  conformation  can adopt other conformations  such as 1$ and  from which  C3 to C8 and C3 to C6 bonding modes are possible g i v i n g , u l t i m a t e l y , products XIV and _XV, respectively. Solvent E f f e c t s The one general solvent e f f e c t observed  i n this series i s  shown i n Table II. I t would seem, therefore, that r i n g closure of b i r a d i c a l intermediate XI occurs p r e f e r e n t i a l l y between carbons 3 and 24a 6 i n benzene.  In a hydroxylic solvent, i t has been suggested  that  hydrogen bonding between b i r a d i c a l and solvent might lead to l o c a l i z a t i o n of the electrons at carbons 3 and 8 (XIV ). 1  Closure between these centres  - 38 Table II. Product Ratios Obtained l n Benzene (unparentheslsed) and t e r t - B u t y l Alcohol  would then explain the p r e f e r e n t i a l formation of product type XIV i n t e r t - b u t y l alcohol.  XIV  The a l t e r n a t i v e structure, XIV", f o r such a  XIV"  - 39 -  solvated species would be a 1,3 b i r a d i c a l which can only collapse to the s t e r i c a l l y unfavored cyclopropyl d e r i v a t i v e .  Quantum Y i e l d and Quenching Studies  24b  The substrate chosen f o r study was compound 9^ which had been 24a shown to give t r i c y c l i c products 9A and j)B_ i n combined y i e l d s of 80% The quantum y i e l d s f o r appearances of enone-alcohol, 9A and diketone 9B  24b were 0.066 and 0.089 respectively  .  These low quantum y i e l d s may  r e f l e c t , among other p o s s i b i l i t i e s , reaction from an inherently less reactive state than a pure n,ir* excited state or r e v e r s i b l e hydrogen 24b transfer.  Quenching studies  showed that product 9B a r i s i n g from  Y-hydrogen abstraction by carbon i s formed from a t r i p l e t excited state. The formation of 9A, a g-hydrogen abstraction product, could not be quenched, however, showing that t h i s process occurs from a very s h o r t - l i v e d t r i p l e t or a s i n g l e t state, a r e s u l t i n accord with the finding o f Agosta and 25d Cormier with a  i n the g-hydrogen abstraction reaction of a-methylene ketones. state.  Tr,Tr*  As mentioned e a r l i e r , hydrogen abstraction by enone carbon i s associated  - 40 -  Stereoelectronic Requirements Both 8- and y -hydrogen abstraction reactions seem  to require  that the hydrogen to be abstracted be trans to the bridgehead hydrogens or substituents.  Thus, compound _11 undergoes both processes while no 24b  hydrogen abstraction occurs on i r r a d i a t i n g 10  .  This i s best  understood by examining the possible conformations which these substrates can adopt i n s o l u t i o n .  These are shown i n Scheme 12 where C5 and C8  hydrogens c i s to the bridgehead substituents are shown by X and those trans are represented  by Y.  I t i s only i n conformations A and B, that  the c i s hydrogen (X) comes within less than 3.5A of the oxygen, and  - 41 -  i t i s i n these same conformations that the C-H bond to be broken i s orthogonal to the adjacent ir-system so that the developing r a d i c a l centre i s 24a denied s t a b i l i z a t i o n through d e r e a l i z a t i o n  .  The abstraction of  only hydrogens i n p o s i t i o n Y i s also i n agreement with the observation 40 made by Turro and coworkers  that only the y-hydrogen  which i s i n the  plane of the carbonyl group ( i . e . the p o s i t i o n of the l o c a l i z e d h a l f vacant n o r b i t a l of the  n-Tf*  state) i s abstracted.  Other Reactions  The preceding discussions have been concerned with only hydrogen abstraction processes. leading to oxetane and cage  Intramolecular c y c l o a d d i t i o n reactions  products have been found to occur only  i n substrates which have no abstractable hydrogen which leads one to conclude that these reactions compete poorly with intramolecular hydrogen abstraction i n tetrahydro-l,4-naphthoquinones.  3.  Objectives of Present Research  During the course of the previous discussion the p o s s i b i l i t y of the v a r i a t i o n i n product types being due to the conformational m o b i l i t y or the lack thereof of the b i r a d i c a l intermediate was  raised.  Most important, there seems no doubt as i n other hydrogen abstraction reactions, r e a c t i v i t y i n t h i s s e r i e s also requires that the substrates f u l f i l l some geometric requirements. ments?  What are these require-  Is the p a r t i t i o n i n g of the b i r a d i c a l conformationally controlled?  In the f i r s t published works  22 23 ' on the parent compound, extensive  - 42 -  polymerization was observed both i n the s o l i d and .in solution.  Since  24a the l a t e r work of Scheffer and coworkers  was carried out using s e l e c t i v e  i r r a d i a t i o n , the question of whether the change from intermolecular to i n t r a molecular reaction was due to the i n t r i n s i c properties of two d i f f e r e n t excited states needs to be answered.  Djerassi  and coworkers, i n a  41 series of papers  , have established that the Y-hydrogen  abstraction  observed i n the mass spectrometer when carbonyl compounds are bombarded with electrons i . e . the McLafferty rearrangement, does not occur i f the o  Y-hydrogen i s further than 1.8A from the abstracting oxygen. Recent 42 work by Henion and Kingston has revealed that, contrary to e a r l i e r 43 calculations , the hydrogen to be abstracted need not be i n the plane of the carbonyl group.  S p e c i f i c a l l y they found that, the angle x  between the i t i n e r a n t hydrogen atom and the plane of the carbonyl group (Figure  -5) has an operational l i m i t , namely, 8 0 ° > x ° ^ 0 ° .  Figure 5.  Although,  Operational D e f i n i t i o n of the Angle x.  the Norrish Type II r e a c t i o n i s analogous to the McLafferty rearrangement, one would not expect i t to have the same geometric requirements as the McLafferty rearrangement because, unlike the l a t t e r , the Type II reaction occurs from e l e c t r o n i c a l l y - e x c i t e d states and "the geometry of this state need not be the excited molecules.  same as those of. ground state or v i b r a t i o n a l l y i  - 43 -  Not s u r p r i s i n g l y , Lewis and coworkers  found that compound  XVI, i n which the geometry of closest approach of the y-hydrogen to the o  oxygen does not allow these two atoms to come any closer than  2.2A  (as measured by Dreiding models), s t i l l undergoes the Norrish Type II  etc.  XVI  reaction. then?  Over what distances can these hydrogen abstractions occur  In photochemical hydrogen abstraction, i s the hydrogen 43  required to l i e i n the plane of the carbonyl group as e a r l i e r proposed . ? As mentioned e a r l i e r , most compounds which are conformationally mobile i n f l u i d media, c r y s t a l l i z e out i n j u s t one conformation which can be accurately determined by X-ray d i f f r a c t i o n methods. from the X-ray data are useful parameters and intermolecular distances.  Also obtainable  such as bond distances, angles  So, the i n i t i a l geometry of a s t a r t i n g  material can be accurately determined provided i t i s c r y s t a l l i n e . Furthermore, due to the r e s t r i c t i o n s of atomic and molecular movements imposed by the c r y s t a l l a t t i c e , most s o l i d reactions are topochemically 12 45 controlled ment.  '  i . e . they occur with minimum atomic and molecular move-  This means that a substrate, S, w i l l react within the c r y s t a l  l a t t i c e without gross changes i n conformation.  I t also means that an  - 44 -  intermediate such as the one postulated i n the photochemical hydrogen abstraction reactions of tetrahydro-l,4-naphthoquinones would, most l i k e l y , have the same conformation as the substrate and close to product(s) from that conformation. Thus, the study of these reactions i n the s o l i d s t a t e , when used i n conjunction with the X-ray s t r u c t u r a l data, promises to shed l i g h t on the geometric requirements f o r these reactions. eleven compounds were chosen f o r study.  9  10  To do t h i s ,  Their structures are shown below.  11  - 45 -  These s u b s t r a t e s ,  taken as a whole, e x h i b i t e d  8, Y, Y  , oxetane, and  24  cage compound f o r m a t i o n r e a c t i o n s  i n solution  as the t a b l e below shows.  Table I I I Substrate  1  1  Yes  2.  Yes  No  No  No  No  2  No  Yes  No  No  No  Oxetane  •X  Cage  Compound  No No No No R e a c t i o n Type Observed i n S o l u t i o n  -.  -  -  5.  Yes  No  No  No  No  6.  Yes  No  No  No  No  _7_  Yes  No  No  No  No  No  No  No  Yes  No  Yes  No  Yes  No  No  10  No '  No  No  Yes  Yes  11  Yes  No  Yes  No  No  A  _9  -  -  A l t h o u g h compounds^ and 10 do not undergo hydrogen a b s t r a c t i o n r e a c t i o n s , i t was  o f i n t e r e s t to f i n d out i f t h e i r c y c l o a d d i t i o n r e a c t i o n s  a l s o o c c u r from  the same c o n f o r m a t i o n as t h e hydrogen a b s t r a c t i o n r e a c t i o n s , o f the o t h e r  com-  24c pounds.  I n p a r t i c u l a r , i t has been s u g g e s t e d  might be o c c u r r i n g  t h a t cage compound  from the same c o n f o r m a t i o n as the hydrogen  formation  abstraction  - 46 -  reactions, since an a l t e r n a t i v e conformation such as C which brings the two n-systems c l o s e r together i s disfavored by bridgehead methyl eclipsing.  - 47 -  Results and Discussion  Preparation of Substrates  Without exception a l l of the substrates investigated were made by the D i e l s - A l d e r addition of a quinone to a diene. Most of the quinones and dienes used were r e a d i l y a v a i l a b l e from commercial sources.  Below i s a summary of the synthetic schemes used  to obtain substrates 1-11. 56,83-Dimethyl-4ag ,5,8,8ag-tetrahydro-l, 4-naphthoquinone, 1_.  ... r e f .  95  6,7-Dimethyl-4aB ,5,8,8ag-tetrahydro-1,4-naphthoquinone, 2_.  • • r e f . 96  4ag,5 ,8,8aB-Tetrahydro-l,4-naphthoquinone, 3_.  ... r e f . 55  - 48 -  6,7-Diphenyl-4a3,5,8,8a8-tetrahydro-1,4-naphthoquinone, j4.  FSJH  o o  2  2  2H n a sC-CC ri^-'g^C H C  C  H  6  6  5  S C  N  N N i NH; NH. I  0  9  2CH.SCH 3  3  2NaH  2CH SCH" 3  2  C HC—CC H 6  C H ^  C H 6  5  6  8  - 51 2,3,4aB ,6,7,8af3-Hexamethyl-4ag,5,8,8a$-tetrahydro-1,4-naphthoquinone, 9_.  .. . r e f . 102  9  2,3,4aB,5a,8a,8a8-Hexamethyl-4aB,5,8,8aB~tetrahydro-l,4-naphthoquinone,  10  ... r e f . 24b  2,3,4aB,5B,80,8aB-Hexamethyl-4aB,5,8,8aB-tetrahydro-l,4-naphthoquinone, 11  ... r e f . 24b  11  - 52 -  A l l substrates were meticulously p u r i f i e d by two or more r e c r y s t a l l i zations before use.  The melting points and s p e c t r a l data of a l l  were i n good agreement with the l i t e r a t u r e values.  The NMR  spectra of  these compounds and of the products obtained by i r r a d i a t i n g them i n the s o l i d state are given i n the Appendix. Unless otherwise stated, the apparatus f o r the s o l i d state reactions was a s p e c i a l l y designed photochemical reactor which allowed for evacuation of the reaction chamber to <0.05 t o r r . temperatures were chosen so as to be below the eutectic  Reaction  temperature  of the reaction mixture comprising product(s) and s t a r t i n g material. . The eutectic temperature was determined by d i f f e r e n t i a l scanning calorimetry using varying compositions of crude reaction mixture and s t a r t i n g material.  One such scan i s shown i n Figure 6.  Uncorrected eutectic  320 Figure 6.  325 330 335  K  Uncorrected Endothermic T r a n s i t i o n f o r 1 + IA Eutectic Mixture. • <.  - 53 -  Reaction temperatures were maintained within f±5° by a c i r c u l a t i n g coolant from an U l t r a Kryomat.  The temperature at the  reaction s i t e was monitored by a copper-constantine thermocouple and read on a d i g i t a l m i l l i v o l t m e t e r .  D e t a i l s on the apparatus and  method of use are given i n the Experimental section.  - 54 -  1.  Intermolecular [^2 + ^2] Dimerization  5a,8a-Dimethyl-4a 3,5,8,8a3-tetrahydro-1,4-naphthoquinone, _1 s.  i_ Large yellow c r y s t a l s of 1 were obtained by c r y s t a l l i z a t i o n from a solvent mixture comprising petroleum ether and d i e t h y l ether. A large, well-formed c r y s t a l of 1 measuring 0.40 x 0.70 x 1.0 mm was used for X-ray data c o l l e c t i o n . The X-ray structure determinations of t h i s and other compounds discussed in t h i s manuscript were c a r r i e d out by Dr. James Trotter and Dr. Simon E.V. P h i l l i p s of t h i s department and have been published as a series of papers i n Acta CrystallographicaJi.  Reference  for the i n d i v i d u a l structures are given with the c r y s t a l data. Unit c e l l and i n t e n s i t y data on 1 were measured using a Datex automated G.E. XRD 6 diffractometer with Cu Ka radiation and the 6-26  scan technique.  Accurate unit c e l l constants were obtained  by a least-squares refinement method using 26 values of 18 manually 46 centred r e f l e c t i o n s .  The structure was solved by d i r e c t methods  using i n t e n s i t y data from 1557 independent  r e f l e c t i o n s and refined  by the f u l l - m a t r i x least-squares procedure to an R value of 0.048.  - 55 -  C r y s t a l Data  C  12 14°2' H  m  o  n  o  c  l  i  n  i  c  >  space group P2^/c with a=7.189(1),  b=22.241(4), c=6.843(1) A, 8=106.51° and Z=4.  The molecules occur  i n pairs related by centres of symmetry, X (Figure 7).  Figure 7.  Stereo diagram of an adjacent p a i r of molecules of 5a,8adimethyl-4aB,5,8,8a8-tetrahydro-l,4-naphthoquinone, 1^, with 50% p r o b a b i l i t y v i b r a t i o n e l l i p s o i d s f o r non-hydrogen atoms. The centre of symmetry i s indicated by X. E l l i p s o i d s are shaded f o r one molecule and unshaded f o r i t s centre of symmetry related neighbour f o r c l a r i t y .  - 56 -  I r r a d i a t i o n of c r y s t a l s of 1^ i n vacuo at temperatures below the eutectic temperature (52.5°) through a Corning glass f i l t e r transmitting  A >_ 340 nm gave only one product.  The l a t t e r c r y s t a l l i z e d  from a solvent mixture comprising chloroform and hexane as small, c o l o r l e s s , sparkling  plates.  The product c o r r e c t l y analyzed f o r the dimer C2^H2g0^. In the i n f r a r e d , the c r y s t a l l i z e d and the crude product had i d e n t i c a l spectra.  Both had carbonyl absorptions at 5.82 and 5.90 u.  The  nuclear magnetic resonance spectrum had a s i n g l e t at 63.47 which was i n d i c a t i v e of cyclobutane r i n g protons.  For comparison, the  cyclobutane r i n g protons of compounds XVII and XVIII have been reported 48 49 at 63.90 and 62.90 respectively  0  0  0  o  '  .  The lack of coupling between the  XVII  cyclobutane r i n g protons i s due to the symmetry of the molecule. In order to determine the stereochemistry of the dimer, one of the c r y s t a l s measuring 0.40 x 0.25 x 0.10 mm was used f o r X-ray structure  determination. C e l l constants were determined and refined  using 20 values from 17 r e f l e c t i o n s .  Intensity  data were c o l l e c t e d  as f o r the monomer from 1458 independent r e f l e c t i o n s .  The R value  - 57 -  a f t e r refinements was 0.050.  Crystal D a t a  C  24 28°4' H  4 7 a  m o n o c l i n i c  »  space group Vl^/c with a=ll.393(1), b=8.029(1),  c=10.771(5) A, 8=91.04(1)° and Z=2.  The molecule i s centrosymmetric  and has a planar four-membered r i n g (Figure 8).  •I  i  Figure 8.  Stereo diagram of dimer IA i n an o r i e n t a t i o n analogous to that of the monomer 1.  - 58 -  The formation of 5,8,15,18-tetramethylpentacyclo[10.8.0.0 ' .0 • .0 ' ]eicosa-6,16-dien-3,10,13,20-tetrone, IA, 2  11  4  9  14  19  from the monomer 1^ formally involves bond  formation between carbons  3 and 2' and between carbons 2 and 3' of adjacent monomer p a i r s related by a centre of symmetry. diagrammatically  The r e a c t i o n i s depicted  below:  17  With the a i d of a stereo viewer, i t can be seen from the arrangement of monomer p a i r s (Figure 7) that the C3, C2 double bond of one partner i s aligned p a r a l l e l to the C2', C3' double bond of i t s adjacent partner.  Such an arrangement  coupled with a short centre-to^centre double  o  bond  contact of 4.040A between these two ir systems allows f o r good  overlap of the p o r b i t a l s .  The separation, d, between the two double  c  - 59 -  bonds i s within the l i m i t 4.2 > d > 3.5 A established by Schmidt and c o w o r k e r s ^ ^ * ^ f state.  o  r  experimentally  photodimerizations i n the s o l i d  As Table IV shows, the chemical y i e l d f o r the 1 ->- LA  conversion was nearly quantitative both at low and high conversions of the monomer.  Table IV. Product Y i e l d s f o r the 1 -»• IA Conversion  Reaction Temperature Room Temperature (uncontrolled)  % Conversion  % Yield  17  91  -1.2°  to -0.7°  37  87  -1.2°  to -0.5°  56  94  -2.0°  to -1.3°  79  96  -1.5°  to -1.0°  79  96  -3.0°  to -2.0°  100  89  In contrast to the above s o l i d state dimerization, compound 1 undergoes intramolecular yhydrogen abstraction when i r r a d i a t e d i n 24a solution  . The product of t h i s reaction, 1B_, a r i s e s from the  abstraction of one of the C9 hydrogens by 0(1) followed by bonding between carbons 3 and 9 and subsequent ketonization.  Although the  nearness of one of the C(9) hydrogens to 0(1) i n the c r y s t a l  (H'  #,,  0  o  distance = 2.38 A) makes the abstraction conceivable  i n the s o l i d  state, the subsequent collapse of the b i r a d i c a l intermediate  to 1B_ i s  - 60 -  not l i k e l y to be permissible within the c r y s t a l l a t t i c e since C3 and C9 are quite remote from each other, i n the c r y s t a l of the substrate.  hv  solution  (1) 3,9 bonding ( ) keronization 2  6,7-Dimethyl-4aB. 5.8 .8aB - tetrahydro-1,4-naphthoquinone, 2 A second example of photodimerization:in the s o l i d state was  provided when c r y s t a l s of compound 2_ were i r r a d i a t e d at long  wavelength (A >_ 340 nm)  below the e u t e c t i c temperature (109.5°).  The sole product of the reaction, 2A,  c r y s t a l l i z e d from a c e t o n i t r i l e  s o l u t i o n as c o l o r l e s s , sparkling p l a t e s . these c r y s t a l s was Product  The i n f r a r e d spectrum of  i d e n t i c a l to that of the crude product. 2A correctly analyzed f o r the dimer C24 28^4'  had carbonyl absorption at 5.85  H  y i n the i n f r a r e d .  I t :  In the nuclear  - 61 -  magnetic resonance spectrum, there were no signals i n the 66.0 - 7.0 region i n d i c a t i n g the absence of conjugated v i n y l hydrogens.  A  s i n g l e t s i t e d at 63.64 was assigned to cyclobutane ring protons by analogy to previous c i t e d examples.  The p o s i t i o n s of a l l other  protons were comparable to the positions of the corresponding protons of monomer 2_.< The ultimate proof of the assigned structure came from X-ray c r y s t a l structure determination. out  Data c o l l e c t i o n was  carried  on a piece of c r y s t a l measuring 0.07 x 0.25 x 0.75 mm which was  cut from a larger c r y s t a l . refined  C e l l parameters were determined and  from 10 r e f l e c t i o n s .  The structure was solved as for  compound JL using i n t e n s i t y data of 1443 independent r e f l e c t i o n s . The f i n a l R value was 0.065. 47b C r y s t a l Data ^24^28^4'  m o n o c  li i » n  c  space group P2^/c with a=15.247(1),  b=6.2776(6), c=10.1949(7) A, 3=93.19(1)° and  Z=2.  - 62 -  As the stereo diagram of the dimer shows, Figure 9, t h i s dimer l i k e IA has a planar cyclobutane ring and i s  Figure 9.  centrosymmetric.  Stereo diagram of 2A. Non-hydrogen atoms are shaded f o r one of the monomer units of the union and open f o r the other for c l a r i t y .  - 63 -  As i n the case of monomer JL, the 2_  2A conversion i s  quantitative both at low and high conversions (Table V).  Table V.  Product Y i e l d s f o r the 2  Reaction Temperature  2k Conversion  % Yield  % Conversion  Ambient  25  99  Ambient  40  97  Ambient  61  96  In contrast to i t s dimerization i n the s o l i d state, compound 2_ undergoes intramolecular $-hydrogen abstraction to give photoproducts 2JB, 2C_ and 2D i n s o l u t i o n .  The r e l a t i v e y i e l d s of 24a  these products were found to be solvent dependent  bonding  - 64 -  4ag ,5 ,8, 8a8-Tetrahydro-1,4-naphthoquinone, 3_  The parent compound of t h i s series of tetrahydro-1,4naphthoquinones, _3, provided a further example of photodimerization i n the s o l i d state. I r r a d i a t i o n of c r y s t a l s of 3^ at long wavelength,  A >_ 340 nm,  below the e u t e c t i c temperature (49.4°) afforded photodimer 3A i n quantitative y i e l d  (Table V I ) .  hv  solid  state  -SA.  Table VI.  Product Yields f o r the 3 -> 3A Conversion % Yield  Reaction Temperature  % Conversion  Ambient  16  86  Ambient  19  80  Ambient  36  100  Ambient  77  75  " 0.0 - 4.3°  94  92  - 65 -  Dimer 3A c r y s t a l l i z e d from chloroform s o l u t i o n as c o l o r l e s s f l a k e s , the i n f r a r e d spectrum of which was i d e n t i c a l to that of the crude product and also to that of a photolyzed KBr p e l l e t containing 3_. It c o r r e c t l y analyzed f o r the dimer ^20^20^4" Since the c r y s t a l s obtained from chloroform were unsuitable for X-ray s t r u c t u r e determination, the dimeric structure 3A was deduced from spectroscopic data. In the i n f r a r e d , cyclobutane r i n g v i b r a t i o n s are not as well defined as are those of cyclopropanes"*^.  Derfer and coworkers"*^" reported  that seven substituted cyclobutanes which they investigated absorbed i n -1 the 920-910 cm region.  52 Reid and Sack followed up with a report  that when a l l the cyclobutane ring carbons are s u b s t i t u t e d , the absorpt i o n s are s h i f t e d to the 888-868 cm coworkers  53  region.  More recently, Dekker and  -1 reported absorptions i n the 1000-850 cm region which they  a t t r i b u t e d to the cyclobutane ring v i b r a t i o n s i n the 920-850 cm region which may be taken as i n d i c a t i v e of the presence of a fourmembered r i n g .  The carbonyl chromophore absorbed at 5.85u.  In the Raman, cyclobutanes are reported"*^ t e r i s t i c C-C s t r e t c h at 933 cm ^.  to have a charac-  Dimer 3A had an absorption at 935 cm ^  i n the Raman. The nuclear magnetic resonance  spectrum was informative. A  s i n g l e t at 63.64 was assigned to the cyclobutane r i n g protons.  This  i s i n good agreement with 6 values of 3.47 and 3.64 f o r the c y c l o butane protons of IA and 2A respectively.  The other assignments  - 66 which a r e g i v e n below compare w e l l w i t h t h e a b s o r p t i o n s o f c o r r e s p o n d i n g p r o t o n s i n t h e monomer.  3_  _3A_ Absorptions P r o t o n type  Monomer _3_  a  6.57(s)  3.64(s)  b  5.63(m)  5.70(m)  c  3.15(m)  3.20(m)  d  2.28(m)  2.30(m)  All  Dimer ^A  t h e s p e c t r o s c o p i c d a t a summarised above and t h e  e l e m e n t a l a n a l y s i s l e d t o t h e i d e n t i f i c a t i o n o f t h e dimer as pentacyclo[10.8.0.0  2  * .0 ' .0 ' ]eicosa-6,16-dien-3,10,13,201 1  4  9  1 4  1 9  t e t r o n e , 3A o f as y e t u n a s s i g n e d In attempts f o r X-ray  stereochemistry.  t o o b t a i n c r y s t a l s of 3A which a r e s u i t a b l e  s t r u c t u r e d e t e r m i n a t i o n , 3A was c r y s t a l l i z e d from a number  of s o l v e n t s i n c l u d i n g g l a c i a l a c e t i c a c i d and a c e t o n i t r i l e . The  infrared  spectrum  o f c r y s t a l s o b t a i n e d from  glacial  a c e t i c a c i d was i d e n t i c a l t o t h a t o b t a i n e d by c r y s t a l l i z i n g  from  30 1  40 I  5.0 1  MICRONS  6.0 i  .  7.0  8.0  9.0  10  12  I  i  i  l  i  1  16  1  20 1—i  1  WAVENUMBER (cm" ) 1  Figure 10.  Infrared spectra of KBr p e l l e t s containing 4-5% by weight of Dimer 3A (Top) and Dimer 3B (Bottom). Ordinates have been shifted f o r c l a r i t y .  30 40 1—r1 -  - 68 ~  acetonitrile.  These c r y s t a l s are judged to be i d e n t i c a l and w i l l be  subsequently referred to as 3B.  As Figure 10 shows the i n f r a r e d  spectrum of 3B_ g r e a t l y resembles that of the i n i t i a l dimer 3A. Nevertheless, the two spectra are not i d e n t i c a l . The absorption spectra of 3A and 3_B c r y s t a l s i n the Raman were also d i f f e r e n t . 3B was at 931 cm  The c h a r a c t e r i s t i c cyclobutane C-C stretch i n  \  The nuclear magnetic resonance spectrum of 3B was however, i d e n t i c a l to that of 3A.  The 3B_ c r y s t a l s c o r r e c t l y analyzed f o r the  dimer C ^ H ^ O ^ One of the 3B c r y s t a l s obtained as c o l o r l e s s , sparkling l i t t l e rods and measuring 0.50 x 0.30 x 0.30 mm was used f o r X-ray structure determination. Accurate c e l l constants were obtained from 28 values of 15 manually centred r e f l e c t i o n s and refined by the least-squares refinement method.  Intensity data from 1488 independent 47b  r e f l e c t i o n s were c o l l e c t e d and treated as described  .  The R value  a f t e r refinements was 0.037. 47b C r y s t a l Data C  20 20°4'' H  m o n o c l i n i c  »  space group ?2^/c with a=ll.7302(5) ,  b=6.4142(2), c=10.9331(5) A, 8=114.624(3)° stereo diagram of dimer 3B.  and Z=2.  Figure 11 i s a  -  Figure 11.  69 -  Stereo diagram of the 3B molecule. Non-hydrogen atoms are shaded f o r one of the monomer u n i t s and open f o r the other monomer unit f o r c l a r i t y .  The v i t a l question i s whether or not the centrosymmetric dimer 3B i s the o r i g i n a l product of the photodimerization of crystals 53 54 of 3_. ' Because of reports  '  of syn->-anti isomerizations of cyclo-  butanes and other small rings by a c i d i c reagents such as s u l f u r i c and phosphoric acids, i t was suspected, at f i r s t , that 3A and 3B might be stereoisomers. If one allows that no isomerization about the decalin r i n g junction occurs during the dimerization, then the number of  - 70 -  possible stereoisomers of the dimer i s only two - one of these, the "syn" isomer, a r i s e s when monomer p a i r s are oriented i n a mirrorsymmetric fashion and the other, the " a n t i " isomer a r i s e s from a  mirrorsymmetric  pair  - 71 -  centrosymmetric p a i r of monomer u n i t s .  The assumption made above i s  j u s t i f i e d by the previously described dimerizations (1 -*• IA and 2_ -*• 2A) i n which configurations about the d e c a l i n bridgeheads are maintained during the r e a c t i o n and also because such isomerizations proceed v i a the enolate ions and require b a s i c catalysts"'"'. Since 3B_ c r y s t a l s have been shown by the X-ray structure to be the " a n t i " isomer, attempts were made to e s t a b l i s h whether or not the o r i g i n a l dimer 3A was the "syn" isomer.  The method of choice  was the j o i n t use of i n f r a r e d and Raman spectroscopy as described by Z i f f e r and Levin"'*' for use i n d i f f e r e n t i a t i n g dimers having centres of symmetry, C^, from t h e i r non-centrosymmetric  isomers.  In t h i s scheme, for a given sample, absorptions i n the Raman and i n f r a r e d which occur at the same frequency, ±5 cm \ are termed coincidences.  For a molecule possessing a  symmetry element,  the infrared and Raman absorptions are, mutually exclusive i . e . a v i b r a t i o n which i s i n f r a r e d active i s Raman i n a c t i v e and v i c e - v e r s a . So, for a  and a non-C^ isomeric p a i r , there w i l l be, i n general,  more coincidences f o r the non-C^ member than f o r the centrosymmetric isomer.  For example, Z i f f e r and Levin"^ found that the head-to-head  dimer of cyclopentenone  which lacks a centre of symmetry had 84% of  i t s Raman l i n e s c o i n c i d i n g within ±5 cm ^ with i t s i n f r a r e d l i n e s while the centrosymmetric h e a d - t o - t a i l dimer had only 25%. As molecular s i z e increases, however, the number of "accidental" coincidences also increases so that the d i f f e r e n t i a t i o n by t h i s method  - 72 -  becomes l e s s clear-cut. . For example, the non-C^ and  isomers of  the dimer of 1-indenone had 67% and 38%, r e s p e c t i v e l y , of t h e i r Raman l i n e s coinciding with t h e i r i n f r a r e d l i n e s .  Although, the 29%  d i f f e r e n c e here i s not as s t a r t l i n g as i n the previous example, i t was thought s u f f i c i e n t f o r a preliminary d i f f e r e n t i a t i o n i f indeed 3A and 3B are mirrorsymmetric and centrosymmetric, respectively. Dimer 3A had, by this a n a l y s i s , 45% of i t s Raman l i n e s coinciding with i t s i n f r a r e d l i n e s while the centrosymmetric dimer 3B had 39%. The 6% difference here i s r e a l l y too small to ascribe to mirrorsymmetric, centrosymmetric c o n f i g u r a t i o n a l isomers.  On the other  hand, i f one assumes that dimer 3A i s also centrosymmetric, then one i s l e f t to explain the differences i n the i n f r a r e d spectra of 3A and 3B. Given the supposition that 3A and  are i d e n t i c a l , the  differences between the two i n f r a r e d spectra can be due to contaminat i o n of the two samples by d i f f e r e n t impurities and/or d i f f e r e n t intermolecular coupling effects"* . 7  The f i r s t of these p o s s i b i l i t i e s  i s u n l i k e l y since d i f f e r e n t batches of c r y s t a l s obtained from the same solvent from d i f f e r e n t sources had i d e n t i c a l spectra.  Furthermore,  the i n f r a r e d spectra of these c r y s t a l l i z i n g solvents revealed that the c r y s t a l s were not contaminated by any of them.  This leaves one  with the l i k e l i h o o d that the i n f r a r e d s p e c t r a l differences merely r e f l e c t d i f f e r e n t orientations of the i n d i v i d u a l molecules within the c r y s t a l .  There i s ample documentation of these c r y s t a l packing  - 73 -  e f f e c t s i n the i n f r a r e d absorption spectra of s o l i d s  .  To prove  that the absorption differences are due to intermolecular e f f e c t s , one would normally need to record the i n f r a r e d spectrum of a s o l u t i o n or melt where such e f f e c t s are absent or l e s s pronounced. Unfortunately, the i n s o l u b i l i t y of 3A and 3B c r y s t a l s i n addition to t h e i r thermal i n s t a b i l i t i e s near t h e i r melting points l e d to the f a i l u r e of these methods.  Nevertheless,  examples of pronounced  intermolecular e f f e c t s i n s o l i d state i n f r a r e d absorptions make the supposition of 3A being i d e n t i c a l to  a tenable one. For example,  the spectra of gaseous and s o l i d benzene (Figure 12) taken from reference 57 i l l u s t r a t e the sort of d i f f e r e n c e s which can a r i s e from intermolecular i n t e r a c t i o n s . The gaseous state represents the " f r e e "  _ l 1800  l 1600  I  l 1400  1 IE00  —  i 1000  1— 800  Wove number  Figure 12.  Part of the absorption spectrum of benzene: i s gas and i s s o l i d . Ordinates are s h i f t e d f o r c l a r i t y .  - 74 -  state i n which the observed absorptions are purely those of the i s o l a t e d molecule.  For the c r y s t a l , there are absorptions  arising  from coupling between the v i b r a t i o n s of adjacent molecules i n addition to those due to intramolecular v i b r a t i o n s . molecular  The i n t e r -  component of the absorption spectrum depends on the  r e l a t i v e orientations of molecules within the c r y s t a l and hence, such f a c t o r s as degree of c r y s t a l l i n i t y w i l l a f f e c t the spectrum. This i s manifest  i n the i n f r a r e d spectra of polymer samples i n which  d i f f e r i n g degrees of c r y s t a l l i n i t y can be achieved by c r y s t a l l i z a t i o n . The e f f e c t s of c r y s t a l l i z a t i o n on the spectra of such samples have been reported"^  Dows and o t h e r s " * r e p o r t 9  d i f f e r i n g i n f r a r e d absorptions  other incidences of  i n the s o l i d state which i l l u s t r a t e  intermolecular coupling e f f e c t s .  In one of such examples, Dows  59 and coworkers  report that ammonium azide s o l i d obtained by  sublimation represents a disordered c r y s t a l which becomes ordered on ' warming.  The i n f r a r e d spectra of the disordered and ordered c r y s t a l s  were s i m i l a r but d i f f e r e n t . Crystals of 3A and 3B may, therefore, represent  different  c r y s t a l modifications of the same compound and the differences i n the i n f r a r e d spectra of these two c r y s t a l s dispersed i n KBr matrices may merely be due to d i f f e r e n t intermolecular i n t e r a c t i o n s within each of these two c r y s t a l s . the dimer i n chloroform,  Owing to the n e g l i g i b l e s o l u b i l i t y of  i t i s l i k e l y that the c r y s t a l s formed from  i t form quickly and are disordered.  This i s e s p e c i a l l y true since  - 75 -  the i n f r a r e d spectrum of these c r y s t a l s i s i d e n t i c a l to that of the crude product and there are i n d i c a t i o n s from the packing diagram of the monomer (below) that the dimer molecules as they f i r s t form are at best only semi-oriented. The monomer, 3_, c r y s t a l l i z e d from a solvent mixture of petroleum ether and d i e t h y l ether as well-formed, yellow needles. Owing to the i n s t a b i l i t y of the c r y s t a l i n the X-ray beam, the c o l l e c t i o n of data f o r the structure determination required two pieces of c r y s t a l measuring  0.80 x 0.30 x 0.20 mm each which had been 47c  cut from larger c r y s t a l s . '  The X-ray data  were obtained and  N  treated as i n previous cases.  Accurate unit c e l l constants were  obtained by least-squares refinement of 29 values of 16 manually centered r e f l e c t i o n s .  The i n t e n s i t y data were obtained from 2496  independent  r e f l e c t i o n s and r e f i n e d by the f u l l - m a t r i x least-squares  procedure.  The f i n a l R value was 0.060. 47c  C r y s t a l Data ^20^20^2'  m o n o c  H i » n  c  space group P2^/c with a=5.266(1),  b=24.267(5), c=14.506(4) A, 8=114.50(2)° and Z=8. The packing diagram of monomer 3_ (Figure 13) revealed two c r y s t a l l o g r a p h i c a l l y independent  types of molecules i n the unit  cell.  These have been l a b e l l e d A and B, r e s p e c t i v e l y , i n Figure 13. As can be seen from t h i s diagram, layers of the A type alternate with those of the B type.  Molecules of the A type form an a x i a l repeat  - 76 -  B  F i g u r e 13.  A  B  8  A  S t e r e o d i a g r a m o f the c o n t e n t s o f t h e u n i t c e l l f o r compound 3.  p a t t e r n , i . e . , each m o l e c u l e i s r e l a t e d t p i t s n e a r e s t n e i g h b o u r o  by a c e l l t r a n s l a t i o n o f 5.266 A.  This l a t t e r distance, therefore,  a l s o measures t h e i n t e r m o l e c u l a r d i s t a n c e between t h e m i d - p o i n t s of t h e C2, C3 and C2', C3' d o u b l e bonds.  F u r t h e r m o r e , as can be  seen from t h e s t e r e o d i a g r a m o f a d j a c e n t m o l e c u l e s o f t h e A t y p e ( F i g u r e 1 4 ) , t h e r e i s no o v e r l a p of t h e s e two TT systems.  On  the  o t h e r hand, m o l e c u l e s o f t h e B t y p e o c c u r i n p a i r s r e l a t e d by a c e n t r e of symmetry denoted by X i n F i g u r e 15.  In this  arrangement,  t h e C3, C2 and C2', C3' d o u b l e bonds o f a d j a c e n t m o l e c u l e s a r e p a r a l l e l b u t o f f s e t w i t h t h e C2 o f one m o l e c u l e d i r e c t l y above t h e C2' o f t h e o t h e r .  The C2 t o C2' c o n t a c t i s t h e s h o r t e s t i n t e r m o l e c u l a r o  d i s t a n c e and measures 3.351  A;  The c e n t r e - t o - c e n t r e s e p a r a t i o n o f t h e  - 77 -  Figure  15.  S t e r e o diagram o f a type B m o l e c u l e (shaded e l l i p s o i d s ) and i t s n e a r e s t neighbour (unshaded e l l i p s o i d s ) r e l a t e d by a c e n t r e o f symmetry, X.  - 78 -  two double bonds Is 3.755 A i n t h i s case.  This i s also the  separation between C2 and C3' and between C3 and C2'. With the aid of a stereo viewer, the overlap of the two double bonds can be appreciated.  The arrangement of molecules of the B type are  analogous to that found i n c r y s t a l s of monomer 1 which as previously shown, dimerized  to the centrosymmetric dimer IA.  By analogy to the 1^ -*• IA conversion, the centrosymmetric dimer 3_B r e s u l t s from a topochemically  c o n t r o l l e d dimerization i n  the B stack with C2, C3 of one monomer l i n k i n g up with C3', C2', r e s p e c t i v e l y of i t s nearest neighbour (Figure 15).  The centre-to-  c'entre separation, d, of the two double bonds involved i n t h i s o  dimerization i s 3.755 A which i s shorter than the corresponding separation i n monomer .1 c r y s t a l s and should make dimerization i n o  t h i s stack r e l a t i v e l y more f a c i l e .  Also t h i s distance, d=3.755 A, o  f a l l s within the range 4 . 2 > d > similar photodimerizations  3.5A experimentally  established for  i n the s o l i d s t a t e ^ " ^ ' ^ . o  On the b a s i s of the large separation of 5.266 A between the two double bonds of adjacent p a i r s of molecules of the A type, no dimerization i s expected to occur i n t h i s stack. shown by monomer conversions the case.  However, as  i n excess of 50% (Table VI) t h i s i s not  Dimerization, most l i k e l y , originates i n the B stack  giving r i s e to centrosymmetric dimers i n t e r c a l a t e d into the l a t t i c e of the monomer.  The boundaries between the reacted and unreacted  regions of the c r y s t a l are akin to d i s l o c a t i o n s i t e s since molecules  -  79  -  here may have d i f f e r e n t orientations from those located elsewhere i n the c r y s t a l l a t t i c e .  These boundaries may be s i t e s for further  reaction i n the c r y s t a l .  The lack of formation of the mirrorsymmetric  ("syn") dimer when molecules i n the A stack eventually react may merely r e f l e c t an e n e r g e t i c a l l y unfavorable process of forming a s t e r i c a l l y crowded dimer. As mentioned e a r l i e r i n the Introduction, Cookson and 23 coworkers  reported the formation  of a dimer of 3^ of unknown stereo-  chemistry during t h e i r photolysis of _3.  They reported that f a c i l e  i n t e r n a l oxidation-reduction occurred when they t r i e d to dehydrogenate the dimer to the dimer of naphthoquinone.  They speculated  that t h i s might i n d i c a t e that the dimer had a syn-configuration about the cyclobutane r i n g .  Since the authors i r r a d i a t e d e t h y l acetate  solutions of 3_ rather than the pure c r y s t a l s , i t cannot be said with any c e r t a i n t y that t h e i r dimer and the one reported i n t h i s work have the same stereochemistry  nor i s i t c e r t a i n that t h e i r  'dimer' i s not a c t u a l l y a mixture of stereoisomeric dimers of _3 since such dimerizations i n s o l u t i o n often produce a mixture of syn-, 62 63 and anti-configurated cyclobutane d e r i v a t i v e s ' 64 An attempt was made recently by Dekker and coworkers assign the stereochemistry  to  about the cyclobutane rings of dimers of J3-  and 1_ by comparing t h e i r rates of cleavage with those of naphthoquinone dimers of known stereochemistry  using z i n c and zinc chloride reagent.  Their r e s u l t s were interpreted as i n d i c a t i v e of a syn-configuration  - 80 -  about the cyclobutane ring f o r both dimers, but as the authors themselves cautioned, such a conclusion would be r i s k y since l i t t l e i s known about the mechanism of the r i n g cleavage reaction by zinc, and zinc chloride and about the e f f e c t s of the aromatic ring on one hand and the o l e f i n i c bond on the other.  As the X-ray c r y s t a l  structure shows (Figure 9) the dimer of monomer 2_ i s centrosymmetric and, therefore, has the a n t i - and not the syn-configuration about the cyclobutane r i n g .  This does not r u l e out the p o s s i b i l i t y of  the syn dimer being formed i n the i r r a d i a t i o n of 1_ i n s o l u t i o n and since i t i s not clear from Dekker's report whether the dimers were prepared by i r r a d i a t i n g solutions or c r y s t a l s of 3_ and 2_ respectively, one cannot say whether the dimers they i s o l a t e d were the same as the ones reported here.  I r r a d i a t i o n of 3_ i n Solution  In the solution photochemistry of 3, the presence of a 24a polymeric material i n the r e a c t i o n mixture was indicated  .  This,  no doubt, p a r t i a l l y accounted f o r the low y i e l d of 10%, of the i d e n t i f i e d products.  I t was, therefore of i n t e r e s t to f i n d out i f  t h i s u n i d e n t i f i e d polymeric material contained dimer(s) of _3. do t h i s , benzene solutions of ,3 were i r r a d i a t e d .  To  The amount of s o l i d  deposited during the reaction varied from run to run but never exceeded 49% of t o t a l recovered m a t e r i a l .  The i n f r a r e d spectrum  of the crude s o l i d deposit showed both OH and C=0 absorptions. presence of the OH group was further confirmed by NMR.  The  Mass s p e c t r a l  - 81 -  analysis of the s o l i d showed peaks up to 495 as compared to 324 f o r the dimer of 3_.  These spectral c h a r a c t e r i s t i c s coupled with the  s o l u b i l i t y of the s o l i d i n CHCl^ and acetone show that whatever the structure of t h i s "polymeric" m a t e r i a l , i t contains very l i t t l e of the dimer of 3_.  Preparative GLC of the benzene soluble p o r t i o n of the 24a  reaction mixture confirmed e a r l i e r r e s u l t s  .  These are summarised  i n the equation below.  hv  solution  3D major  Reactive State and Mechanism for the Photodimerization Reactions  Although no mechanistic i n v e s t i g a t i o n s have been c a r r i e d out f o r the photodimerizations of substrates JL, 2_ and J^, analogy can be drawn from numerous examples of such reactions both i n the s o l i d ^ 61 . . . . 62.63 state and i n solution For example, the dimerization of 2-cyclopentenone  in 62  solution has been shown by quenching  studies to be t r i p l e t derived  So are a number of photodimerizations of a,$-unsaturated  cyclic  62 63 ketones  '  .  Nevertheless, a number of photodimerizations both i n  the s o l i d state and in solution are known to occur from the s i n g l e t  - 82 -  ../Ij  solution  61 65 state  '  . The solution photodimerization of coumarin, equations  2 and 3 below, has been shown to occur from e i t h e r the s i n g l e t or the t r i p l e t depending on the reaction conditions^"*.  Very i n t e r e s t i n g l y ,  --(2)  EtOH  singlet-derived  EtOH (C H ) CO 6  5  2  YVA (major)  triplet-derived|  (trace)  •(3)  - 83 -  thymine photodimerizes from the t r i p l e t i n s o l u t i o n but the equivalent s o l i d state reaction occurs from the s i n g l e t state****.  This and  Schmidt's g e n e r a l i z a t i o n that the majority of s o l i d - s t a t e photo-, dimerizations occurs from the f i r s t excited singlet*'"'" would seem to i n d i c a t e that s o l i d state photodimerization  proceeds v i a a r e a c t i v e  state which i s d i f f e r e n t from that which obtains i n s o l u t i o n . the narrow energy separation between the n , T r * s i n g l e t , the  Given  n,Tf*  and the TT,TT* t r i p l e t s i n some of these a,g-unsaturated ketones, i t might very w e l l be that no g e n e r a l i z a t i o n can -be made about the nature of the r e a c t i v e excited species involved i n the photodimerizations of JL, 2 and _3. Whatever the nature of the excited species, there i s general agreement that the r e a c t i o n involves the union of an excited monomer and a ground state monomer. for both s o l i d state  61  This has been experimentally  demonstrated  62 and f l u i d media photodimerizations.  Although  the two new bonds to be formed i n t h i s reaction have been shown to 62 63 occur i n a stepwise fashion f o r dimerizations i n s o l u t i o n concerted  [2 + TT  S  '  , the  2 1 mechanism cannot be ruled out for reactions Tf S  occurring from the s i n g l e t manifold i s necessary before r i n g closure.  f o r which no spin p a i r i n g process The s t e r e o s p e c i f i c i t y of the s o l i d  state reactions of substrates 1_, 2^ and 3^ i n no way i d e n t i f i e s the reaction mechanism, however, since the formation of a b i r a d i c a l which i s frozen i n the conformation of i t s monomer units by the c r y s t a l l a t t i c e could s t i l l give a s t e r e o s p e c i f i c product.  - 84 -  In conclusion, the topochemical p r i n c i p l e has been w e l l demonstrated by the UV induced dimerization of 4a8,5,8,8aB-tetrahydro1,4-naphthoquinone  and two of i t s dimethyl d e r i v a t i v e s .  The stereo-  chemistry of each of the dimers has been unambiguously determined f o r the f i r s t time using single c r y s t a l X-ray d i f f r a c t i o n methods.  - 85 -  2.  Intramolecular Hydrogen Abstraction  6,7-Diphenyl-4aB ,5,8 ,'8a g - tetrahydro-1,4-naphthoquinone,  A.  Compound 4^ c r y s t a l l i z e d out of a solvent mixture of acetone and hexane as well-formed yellow needles.  One of these c r y s t a l s  4  measuring  0.47  x 0.43 x 0.70 mm was used f o r X-ray structure determination.  The method and data treatments are the same as f o r previously reported structure determinations. from 26 values of 19 r e f l e c t i o n s . 3365 independent r e f l e c t i o n s .  Unit c e l l parameters were refined Intensity data were c o l l e c t e d from  The R value a f t e r refinements was 0.053.  C r y s t a l Data^ : 7  C  22 18°2' H  m o n o c  l  i n  b=6.527(2), c=22.112(3) A,  i > c  space group P2/c with a=27.092(4),  g=120.562(9)° and Z=8.  The conformation of  the molecule i s twisted such that the bridgehead hydrogens are staggered with a t o r s i o n angle of 62°. normal;  Bond lengths and angles are  A stereo diagram of the molecule i s shown i n Figure 16. Intermolecular distances mostly correspond to van der Waals  contacts except one notable distance, namely, the distance between 0(2)  - 86 -  of one unit and the H(3) of the nearest molecule.  This distance i s  2.39 A compared to a normal van der Waals contact of about 2.6 A  I r r a d i a t i o n of 4^ both i n KBr and as the pure s o l i d i n vacuo below the e u t e c t i c temperature (151.3°) gave the enone-alcohol 4A expected from the abstraction of a B-hydrogen by oxygen  (Scheme 13) .  As the stereo diagram i n Figure 16 shows, one of the oxygens, namely, 0(1) i s located near and coplanar with one of the C8 hydrogens, H(8B). The abstraction most l i k e l y involves these two atoms.  The interatomic  - 87 -  Scheme 13  2.46A  solid state  distance involved i n the abstraction i s 2.46 A.  The d i r a d i c a l 4/  r e s u l t i n g from B-hydrogen abstraction i s most l i k e l y frozen i n the conformation of i t s precursor.  In that conformation, r a d i c a l centres  o  o  -  1 and 6 are only 3.51 A apart as compared to distances of >4 A for C3, C6 and C3, C8 separations,  respectively.  Closure of b i r a d i c a l 4_' between  centres 1 and 6 gives the observed enone alcohol product 4A.  The  l a t t e r was e a s i l y i d e n t i f i a b l e by i t s i n f r a r e d and NMR spectra.  The  carbonyl absorption of the six-membered r i n g enone came at 5.97u (cf.  5.92 and 5.95y for 4).  2.92y.  The OH absorbed broadly but moderately at  In the NMR of a l l previously encountered enone alcohols of t h i s  general structure, the CIO bridgehead proton absorbed i n the range  - 88 -  3.24 - 2.87 6***. This has become diagnostic f o r the enone alcohol structure. 3.456.  In 4A, t h i s methine appeared as a doublet, J=3 Hz, at  The s h i f t downfield i s l i k e l y due to the deshielding e f f e c t  of the neighbouring aromatic r i n g .  The hydroxyl proton resonated as  a s i n g l e t at 2.736 and was e a s i l y exchanged f o r deuterium when D^O was added. In experimental runs i n which conversion of s t a r t i n g m a t e r i a l to product(s) was c a r r i e d to >17%, a second product, j4B was also i s o l a t e d .  That t h i s product arose from a secondary photolysis  of the primary photoproduct was borne out by the following experimental f a c t s : isolated;  ( i ) at low conversions, 4A was the sole product  ( i i ) the formation of j4B l e d to diminished y i e l d s of 4A  (Table VII) ; ( i i i ) during the photolysis of KBr p e l l e t s of 4_, depletion of 4_  Table VII.  Product Yields f o r the 4^ ) + 4A + 4B Conversion c  Reaction Temperature  % Conversion  % Yields 4A  4B None  -10.4 to -9.8°  17  67  18.5 to 22.0  66  47  8  17.3 to 18.5  >90  33  15  and formation of 4A preceded the appearance of 4B as shown by infrared spectra recorded at 10 minute i n t e r v a l s during the i r r a d i a t i o n ; (iv) 4A dispersed i n KBr or as the pure s o l i d was converted to 4B under  - 89 -  reaction conditions i d e n t i c a l to those used f o r the k_ -»• 4A transformation. Photoproduct 4B c o r r e c t l y analyzed f o r 2 2 1 8 ° 2 C  characterised as 2,3-diphenyltricyclo [5.3.0.0"*  H  a  n  d  w  a  s  deca-2-ene-6,9-dione  on the basis of i t s i n f r a r e d , NMR and mass spectra.  4B It had a carbonyl absorption at 5.73u which i s c h a r a c t e r i s t i c of the infrared absorption of compounds of s i m i l a r structure having 24 the five-membered  r i n g ketone  assignments were made:  .  In the NMR spectrum the following  67.23 - 6.87 (m, 10H, aromatic), 3.23 (m, 2H,  C7 and CIO methines) , 3.07 (nr, IH, C5 methine) , 2.83 (m, 3H, CI and C4 protons), c a l c d  6 9  2.57 (dd, J=20 and 5 Hz IH, C8 exo), c a l c d  2.20 (dd, J=20 and 1.5 Hz, C8 endo).  6 9  The assignment of the C8 exo  and endo protons was based on the disappearance of the 62.57 resonance upon deuterium exchange in basic deuterium oxide and the concomitant collapse of the doublet of doublets at calcd. 62.20 to a broad s i n g l e t at 62.21.  The f a c i l e exchange of t h i s exo hydrogen i n bicyclo[2.2.1]-  heptanone systems has been reported i n the l i t e r a t u r e ^ .  The NMR  absorption pattern of compound 4B i s very s i m i l a r to that of the 24a previously reported analog compound 2_C (Figures 17a and 17b). For  - 90 -  Figure 17b.  A 100 MHz FMR Spectrum of 2,3-Dimethyltricyclo[5.3.0.0 deca-2-ene-6,9-dione, 2C.  *  ]-  - 91 -  example, the exo and endo protons at C8 each resonated as a doublet of doublets at calcd. 62.47 and 2.19  i n 2C.  In photoproduct  4B these  protons also resonated each as a doublet of doublets at calcd. 62.57 and 2.20,  respectively. Since the photochemical behaviour of substrate 4_ has,  hitherto, not been studied i n s o l u t i o n , photolyses of i t i n benzene were also carried out to ascertain i f i t s r e a c t i v i t y i n s o l u t i o n d i f f e r e d from the s o l i d state photoreactivity.  These r e s u l t s are  summarised i n equation 4 below.  Table VIII.  Product Yields f o r the 4(solution^ ^ Duration of I r r a d i a t i o n  4 A  +  4 B  Conversion  Product Ratios 4A:4B  3.0 hours  3:1  3.1  "  3:2  3.9  "  1:2  - 92 -  Unlike the s o l i d state reaction, product 4B i s formed concomitantly with 4A as determined by following the reaction at 0.1 hour i n t e r v a l s using i n f r a r e d spectroscopy.  As i n the s o l i d state  reaction, photoproduct 4A was again found to be photolabile-as shown by  ( i ) the varying r a t i o of 4A: 4B_ as the r e a c t i o n proceeds (Table VIII);  ( i i ) independent photolysis of 4A under the same reaction conditions as f o r the k_ -*- 4A conversion  gave 4B and a compound having 5.68 and  5.80 y carbonyl stretches i n the i n f r a r e d .  Although this l a t t e r  compound was not investigated f u r t h e r , i t probably has the assigned 24 structure 4C since previous investigations  of the photochemistry o f  these tetrahydro-1,4-naphthoquinones i n s o l u t i o n have shown that only photoproducts of t h i s structure absorb at ^5.70 and 5.80 u. Examples of this are given below:  4C  3D C=0  5.68, 5.80  2D  ,M  5.68, 5.80  5.69,  5.81  - 93 -  The formation of ene-diones 4B and 4C from enone a l c o h o l 4A i s not 24a novel.  Scheffer and coworkers  dimethyl enone-alcohol  reported the conversion of the  2JJ to the ene-dione 2C_ i n t e r t - b u t y l alcohol  and 2JB to 2D i n benzene (equation 6 and 7) .  The conversion of an  enone-alcohol to both ene-diones i n benzene was (equation 8).  a l s o l a t e r reported \  - 94 -  50%  50%  The photochemical formation of 4B_ from 4A i s formally a disallowed •~ . [3,3] s u p r a f a c i a l - s u p r a f a c i a l sigmatrppic rearrangement therefore, l i k e l y , a non-concerted reaction. 4A  72  and i s , .  On the other hand, the  4C_ conversion i s a [1,3] s u p r a f a c i a l sigmatropic s h i f t which i s  photochemically allowed. concerted.  I t can, therefore, but need not be,  In both the s o l i d state and i n s o l u t i o n , photoproduct  4B was photostable under the reaction conditions. Turning now  to the primary reaction, namely, the  4A + 4B  reaction i n benzene, analogy i s drawn to e a r l i e r systems studied i n our laboratory i n which both product types were formed as primary 24 71 products  '  .  The formation of both of these products can be  explained by postulating the same d i r a d i c a l intermediate 4_' which was used e a r l i e r to explain the formation of 4A from h_ i n the s o l i d state. As can be seen from Scheme 14, photoproducts 4A and 4B probably a r i s e from d i f f e r e n t conformers of the b i r a d i c a l intermediate 4/. The reason behind t h i s s t i p u l a t i o n comes from the X-ray data as w e l l as the s o l i d state r e s u l t s .  Photoproduct 4B can only form from  b i r a d i c a l 4/ of unspecified conformation i f bond formation occurs between C3 and C8.  This i s not l i k e l y to happen from conformer  4'A  - 95 "  Scheme 14  since these centres are greater than 4A apart.  On the other hand, C l  o  and C6 are only 3.51A  apart in.substrate 4_.  Assuming that the  conformation i n which the molecules c r y s t a l l i z e i s also the preferred conformation i n s o l u t i o n , i t can be seen that the b i r a d i c a l i n t e r mediate may  form and close to the enone-alcohol from t h i s  conformation  i . e . no gross conformational changes are mandatory f o r the 4^ -*• 4A conversion. change.  The 4^ -*• 4B conversion most l i k e l y requires a conformational  Since conformational m o b i l i t y i s p o s s i b l e i n f l u i d media, a  -  96  -  conformer such as 4 ' B i s possible i n s o l u t i o n and not i n the s o l i d state and the now nearness of the C3 and C8 centres would allow product 4B_ to be formed.  The observation that photoproduct 4B  i s the minor product of the primary reaction i n s o l u t i o n i s most l i k e l y a r e f l e c t i o n of the conformational change necessary to allow for i t s formation.  2 , 3 - D i m e t h y l - l » 4 - 4 a B > 9 a B r - t e t r a h y d r o - 9 ,10-anthraquinone,, 6_  Compound 6_ c r y s t a l l i s e d from acetone s o l u t i o n as c o l o r l e s s  rods.  I r r a d i a t i o n of 6_ i n the s o l i d state below the eutectic  temperature ( 1 2 6 . 0 ° ) gave enone-alcohol 6A (equation 9) i n 60%  hv solid  isolated y i e l d .  state  "(9)  The structure of 6A follows u l t i m a t e l y from  comparison of i t s s p e c t r a l data with those of authentic 6A prepared  - 97 -  using the procedure of Scheffer and coworkers^"" . 1  The conversion of  j> to 6A involves the abstraction of a g-hydrogen by one of the oxygens of an excited carbonyl chromophore followed by C9 to C3 bonding.  The transformation i s analogous to the h_ ->• 4A  conversion.  A small piece of c r y s t a l 6_ measuring 1.0 x 0.80 was  x 0.30  mm  cut from a larger c r y s t a l and used f o r the determination of the 73  X-ray structure  .  Unit c e l l constants were r e f i n e d by least-squares  from the observed 29 values of 17 r e f l e c t i o n s . 1313  Intensity data from  independent r e f l e c t i o n s were used for the structure determination.  The R value a f t e r f u l l - m a t r i x refinements was 73 C r y s t a l Data ^16^16^2'  ortn  0.055.  o r h o m b i c , space group Pna2^ with a=15.643(2),  b=5.160(1), c=15.568(2) A, 8=90° and Z=4.  The structure of the  molecule i s shown i n Figure 18. The hydrogen abstracted i n the 6_ -»- 6A conversion i s one of the C l hydrogens.  The interatomic separation between t h i s hydrogen  and the abstracting atom 0(1) i s 2.57 r i s e to a b i r a d i c a l 6/ aromatic r i n g  (Scheme 15).  A.  The abstraction would give  E l e c t r o n d e r e a l i z a t i o n i n t o the  i s expected to aid the s t a b i l i z a t i o n of 6/.  However,  no bond formation involving the aromatic r i n g carbon atoms i s expected since t h i s w i l l r e s u l t i n loss of the s t a b i l i z a t i o n energy associated with the aromatic r i n g .  This leaves only two possible  modes of r i n g closure for biradical, 6/, namely bonding between C9 and  - 99 -  CI and between C9 and C3.  As already mentioned i n the Introduction,  the formation of a cyclopropane systems i s u n l i k e l y  r i n g i n these already r i g i d p o l y c y c l i c  and has to date not been observed.  between C3 and C9 gives r i s e to the observed product  6A.  Bond formation In substrate  6^ the interatomic separation between C3 and C9 i s only 3.46  A so  here as i n the k_ -* 4A transformation, the b i r a d i c a l can form and collapse to the observed product without  any gross changes i n  conformation. Not s u r p r i s i n g l y , i r r a d i a t i o n of degassed solutions of 6_ also gave 6A as the only product because as pointed out, the b i r a d i c a l intermediate 6/ can only close between C3 and  C9.  6,7-Dimethyl-4ag,8ag-dicyano-4ag,5,8,8ag-tetrahydro-1,4-naphthoquinone, 1  Large, sparkling yellow c r y s t a l s of _7 were obtained by c r y s t a l l i z a t i o n from a solvent mixture of acetone and l i g h t petroleum ether.  One c r y s t a l measuring 0.50 X-ray structure determination. least-squares refinement  x 0.40  x 0.40  mm was  used f o r  Unit c e l l constants were obtained by  of the observed 26 values of 23 r e f l e c t i o n s .  - 100 -  Intensity data from 2445 independent r e f l e c t i o n s were used to solve the structure.  The f i n a l R value a f t e r refinements was 0.055.  74 C r y s t a l Data C  14 12 2°2' H  N  m  o  n  o  c  H  n  i  c  »  space group P2^/c with a=8.717(5),  b=12.464(2), c=12.783(5) A, 8=117.87(3)°, and Z=4. the molecule i s given i n Figure 19.  Figure 19.  Stereo diagram of compound ]_.  A stereo view of  - 101 -  I r r a d i a t i o n of ]_, either as a s o l i d dispersed i n a KBr matrix or as the pure s o l i d i n vacuo below the e u t e c t i c temperature (118.5°), gave the enone-alcohol 7A i n 92% i s o l a t e d average y i e l d .  Photoproduct  7A_ was conclusively i d e n t i f i e d by comparing i t s p h y s i c a l  and s p e c t r a l c h a r a c t e r i s t i c s with those of authentic JA. prepared by 24b the method of Scheffer and coworkers The formation of l_k formally involves the abstraction of one of the C8 methylene hydrogens, Hg, by 0(1) and collapse of the r e s u l t i n g b i r a d i c a l through bond formation between carbons 1 and 6. o  The Hg'-'O(l) distance i n the c r y s t a l i s 2.58 A.  The separation of  o  C l and C6 i n the c r y s t a l i s 3.38 A.  So here as i n the two previous  examples, the formation of the b i r a d i c a l intermediate i n t h i s reaction and i t s subsequent collapse to enone-alcohol does not require any conformational changes.  The only other possible but unobserved bonding  modes are between C3 and C6 and between C3 and C8.  The separations o  between these carbons i n the c r y s t a l are 3.86 and >4 A, respectively. Not only are these distances longer than the C l , C6 separation i n the c r y s t a l but the p - o r b i t a l s at these centres are d i r e c t e d away from  - 102 Scheme 16  each other so that overlap between them cannot be achieved. One might expect that l i k e many of the substrates i n t h i s series of tetrahydro-l,4-naphthoquinones, substrate ]_ i n s o l u t i o n might give the ene-diones _7JL and 7C.  I r r a d i a t i o n of degassed benzene  solutions of 1_ gave 74% y i e l d of enone-alcohol _7A and 7% y i e l d of a compound melting at 156 - 158°. s p e c t r a l data:  The latter compound had the following  In the i n f r a r e d i t had cyano stretching frequencies at  4.44 and 4.46 u and a carbonyl stretch at 5.90y.  The single C=0  stretch at 5.90y ruled out both ene-diones T&_ and _7C_.  In the nuclear  magnetic resonance spectrum, i t had two doublets, J^g=10Hz, s i t e d at 67.44 and 6.41, r e s p e c t i v e l y , which integrated f o r IH each.  The  - 103 -  rest of the spectrum had 62.56 (s,2H), 2.45 J=15 Hz, IH), 1.56  (s, 3H) and 1.38  a parent peak at m/e=240.  (s, 3H).  (d,J=15 Hz, 1H), 1.72  (d,  I t s mass spectrum showed  This product, 7D i s t e n t a t i v e l y assigned  the oxetane structure below:  The absence of ene-diones  7JB and _7C_ has  been ascribed to the  prevention of conformational changes even i n solution as a r e s u l t of bridgehead s u b s t i t u t i o n . As an attempt to see i f any s i m i l a r i t i e s exist between the geometries of a substrate and i t s s o l i d state photoproduct, the X-ray structure of enone-alcohol 7A was also determined''"'. view of the molecule i s shown i n Figure 20.  A stereo  As can be seen from  comparing t h i s diagram with that of the s t a r t i n g c r y s t a l _7, the 1_ conversion i s attended by the conversion of the favorable h a l f - c h a i r conformation of the C5-C10 r i n g to a boat form.  The conformation  of the quinone r i n g remains e s s e n t i a l l y the same. During the X-ray structure determination, there were indications that enone-alcohol 7A might be o p t i c a l l y a c t i v e .  The  molecule i t s e l f i s c h i r a l , but one would expect that i n a b i r a d i c a l  7A  - 104 -  Figure 20.  Stereo diagram of enone-alcohol, 7A.  r i n g c l o s u r e , both levorotatory and dextrorotatory molecules should form i n equal proportions giving" racemic 7A.  If crystals  of 7A  were o p t i c a l l y a c t i v e , i t meant that a racemic mixture had been formed during c r y s t a l l i z a t i o n , an uncommon occurrence i n organic chemistry.  When single c r y s t a l s  as w e l l as c l u s t e r s  7A were used i n o p t i c a l r o t a t i o n determinations, i n Table IX were obtained.  of crystals of  the results shown  - 105 -  Table IX.  S p e c i f i c Rotation of Solutions of Crystals of IL  25.5°  Description of C r y s t a l  Single  +3.0°  Single  +2.5°  Single  -67.7°  Clusters  -14.5°  The fact that some of the single c r y s t a l s were levorotatory and others dextrorotatory means that c r y s t a l l i z a t i o n followed..by mechanical separation had effected r e s o l u t i o n of the racemic photoproduct.  ..The fact that the s p e c i f i c  r o t a t i o n of the levorotatory single c r y s t a l i s not equal to that of the dextrorotatory c r y s t a l i s an i n d i c a t i o n that the r e s o l u t i o n i s only p a r t i a l .  Nevertheless, such a spontaneous r e s o l u t i o n through  c r y s t a l l i z a t i o n i s rare.  The h i s t o r i c a l example of t h i s phenomenon 76a  was reported by Louis Pasteur  who  allowed a s o l u t i o n of sodium  ammonium t a r t r a t e to c r y s t a l l i z e by slow evaporation below 27° and was  subsequently able to separate the two enantiomers  by mechanically  picking them apart.  Since then, very few examples of t h i s occurrence  have been reported.  Among these are the spontaneous c r y s t a l l i z a t i o n  of active material from  d l solutions of ( i ) 3,3-diethyl-5-methyl-  2 , 4 - d i k e t o p i p e r i d i n e ^ , ( i i ) n a r c o t i n e ^ , ( i i i ) laudanosine * 7  7  (iv) m e t h y l - e t h y l - a l l y l - a n i l i n i u m i o d i d e  C  7<3<  7  30  and  *.  The c r y s t a l packing diagram revealed that compound _7 represents the crossover from i n t e r to intra-molecular r e a c t i v i t y i n  - 106 -  t h i s s e r i e s of tetrahydro-l,4-naphthoquinones.  Figure 21 shows  portions of adjacent molecules within a c r y s t a l l o g r a p h i c c e l l .  The  TT overlap of the ene-dione double bonds which i s necessary for dimerization i s not achieved due to a s l i g h t t i l t  Figure 21.  of the C2, C3 plane  Neighbouring ene-dione systems of a p a i r of molecules of 1_ viewed perpendicular to the C ( l ) , C(2), C(3) plane.  of the molecule above the plane of the paper r e l a t i v e to the C2 , 1  plane of the molecule below i t (Figure 21).  C3'  The intermolecular  contacts are also much longer than the corresponding  distances f o r O  substrates 1, 2 and 3.  For example the C2 to C2' distance i s 4.37A.  Because of the t i l t of the C2, C3 plane of one of the molecules of the p a i r mentioned p r e v i o u s l y , the C2—C2' distance does not the shortest intermolecular contact.  represent  The l a t t e r turns out to be the  C2 to C3' distance of 4.09& which s t i l l exceeds the sum of the van 68 Waal's r a d i i  of the two atoms by 0.691..  The  centre-to-centre  der  107 -  separation of the double bonds i s 4.1A, and so not only are the o r b i t a l s not-aligned f o r intermolecular overlap but the l i m i t of double  bond separation necessary  crystalline state^ ' 2  3  f o r photodimerization i n the  has a l s o been reached.  Consequently, no  photochemical dimerization was observed when c r y s t a l s of 1_ were irradiated.  2,3,4ag,6,7,8ag-Hexamethyl-4aB, 5,8.8aB-tetrahydro-1,4-naphthoquinone, £  Large, pale yellow c r y s t a l s of 9^ were obtained by c r y s t a l l i z i n g from petroleum ether.  Smaller but better-formed  crystals for  crystallographic purposes were obtained by c r y s t a l l i z i n g from acetone. Crystals obtained from e i t h e r solvent reacted i n i d e n t i c a l fashion  - 108 -  both i n KBr and as the pure s o l i d .  Thus, one may  assume that the  c r y s t a l form i s not changed as. a r e s u l t of change of c r y s t a l l i z i n g solvent.  UV i r r a d i a t i o n of 9^ below the e u t e c t i c temperature  (-16.0°)  led to the formation of enone-alcohol 9A and the ene-dione 9B_ i n • the r a t i o  2:3.  This r a t i o was  invariant below the eutectic at  varying conversions (Table X)  Table X.  as one would expect from a r e a c t i o n i n  Product Ratios and Combined Y i e l d s f o r the 9 ->• 9A + 9B Conversion, i n the S o l i d State  Reaction Temperature  % Conversion  % Recovery  Combined GLC Yields  Ratio 9A:9B  -34.3° to -33.5°  41  91  77%  2:3  -34.7° to -32.5°  54  94  88%  2:3  -33.5° to -30.3°  68  63  46%  2:3  -25.6° to -23.1°  77  71  62%  2:3  -25.3° to -23.4°  88  78  75%  2:3  which both products are primary products.  Y i e l d s are quite high  provided the recovery of reaction mixture from the reactor i s high. The structures of 9A and 9_B were confirmed by comparing their p h y s i c a l and s p e c t r a l data with those of 9A and 9B_ obtained previously and 24 reported i n the l i t e r a t u r e  .  As mentioned i n the Introduction, 9A  and 9JS are thought to derive from d i f f e r e n t excited states, enone  - 109 alcohol 9A from an  n,Tf*  s i n g l e t and ene-dione 91J from a  Tr,Tr*  triplet.  This being the case, i t was of i n t e r e s t to repeat the solution photochemistry, which has hitherto been done only at ambient temperature, at temperatures below the eutectic to see i f the r a t i o of j?A:j)B was the same f o r the solution photolysate as f o r the s o l i d state reaction a t s i m i l a r  temperatures.  Table XI.  summarizes r e s u l t s of the conversion _9 -»• 9A + j)B i n anhydrous ether below the eutectic.  Table XI.  In terms of percentages, t h i s r a t i o d i f f e r s  Product Ratios f o r the 9 -»• 9A + 9B Conversion i n Solution  9 —  Reaction Temperature  e t  !*  e r  hv  > 9A + 9B —  —  Ratio 9A:9B  % Conversion  -33.0° to -31.5°  21  1:2  -31.5° to -29.0°  25  1:2  -32.5° to -31.5°  52  1:2  -31.5° to -29.5°  63  1:2  from the s o l i d state products r a t i o by only 7%, a difference too small to warrant explaining e s p e c i a l l y i n view of the fact that product 24 r a t i o s i n solution may be solvent dependent The X-ray structure of _9 was solved by d i r e c t methods as described^.  The c r y s t a l dimensions were 0.15 x 0.20 x 0.20 mm.  Unit  c e l l constants were obtained by least-squares refinement of the observed  - 110 -  20 values of 15 r e f l e c t i o n s .  The i n t e n s i t y data of 2786 independent  r e f l e c t i o n s were used i n the structure determination.  The R value  a f t e r refinements was 0.088.  Crystal  Data  C  7 7  16 22°2' H  m  o  n  o  c  l  i  n  i  c  »  space group P2 /c 1  b-11.540(4), c=16.674(3) A, 8=92.26(3)° and Z=4. stereo view of the molecule.  with a=7.312(3), Figure 22 gives a  - 111 -  Scheme 17  hu solid state  9A  9B  Photoproduct 9A i s the enone-alcohol product a r i s i n g from abstraction of Hg, one of the C8 hydrogens, by 0(1) followed by bond formation between C l and C6 r a d i c a l centres (Scheme 17). The Hg to  - 1.12 -  0(1) distance i s 2.47A and the CI to C6 distance i s 3.35A. The unobserved bonding modes of b i r a d i c a l 9'A, namely C3 to C6 and C3 to o  C8 were both >4A i n the c r y s t a l of 9_. The ene-dione product, 9B, formally a r i s e s from the abstraction of one of the C5 hydrogens, namely, H^, by C2 giving b i r a d i c a l 9'B which then closes by bonding C3 to C5.  The distance  between the abstractable hydrogen and the abstracting carbon, namely H "'*C2 i s 2.89A i n the s t a r t i n g material 9_. A  i f there are no gross changes i n conformation  As i n previous  cases,  attending the reaction,  one could approximate interatomic separations i n the b i r a d i c a l intermediate to the corresponding substrate.  interatomic distances i n the  The C3, C5 separation i s thus only 3.17A.  Not only i s  the interatomic separation favorable but the geometry of the molecule has the p o r b i t a l s at these centres directed towards each other thus promoting interaction  and u l t i m a t e l y bond formation  (Scheme 17).  As  i n the case of b i r a d i c a l 9'A, the unobserved bonding mode i n b i r a d i c a l 9'B, namely-_C3-tO--C7-,- would have .involved.-bringing- together .carbon • o  centres which are >4A i n the c r y s t a l of the substrate to closer proximity, a process which i s l i k e l y to e n t a i l  conformational  changes impermissible by the l a t t i c e of the host. The 3:2 r a t i o f o r photoproducts 913 and 9A does not r e f l e c t the r e l a t i v e rates for y- vs 3-hydrogen abstraction. below suggests, the rates of formation of products on a number of f a c t o r s .  As the. k i n e t i c scheme 9A and 9B_ depend  For example, the r e l a t i v e population of the  - 113 _  Scheme 18  n,Tr*  and  TT,TT*  states, the rates of decay of these two excited  states and the rates of b i r a d i c a l closure r e l a t i v e to reverse hydrogen transfer w i l l a l l be r e f l e c t e d i n the o v e r a l l rates of formation of these two products. One i n t e r e s t i n g r e v e l a t i o n from the c r y s t a l l o g r a p h i c data i s that the hydrogen which i s abstracted  by enone carbon i s quite  d i s t i n c t from the hydrogen which i s abstracted  by oxygen, i . e . the  g-carbon of the enone system and the oxygen do not compete f o r the same hydrogen i n t h i s reaction, a f a c t which i s not evident  from the  chemical structure of 9_ because of the symmetry of the molecule. Another i n t e r e s t i n g point to be noted i s that from the X-ray c r y s t a l structure, %  can, i n p r i n c i p l e , be abstracted  by either C2  - 114 -  or C3,being 2.89A from C2 and 2.80A away from C3.  Abstraction by C3  would have given b i r a d i c a l 9X which can close to S>C, an unobserved  photoproduct, by bonding centres, C2 and C5. would have proceeded v i a a five-membered  Such an abstraction  t r a n s i t i o n state as opposed  to the six-membered t r a n s i t i o n state that gives r i s e to the observed photoproduct 9B_.  That 9^C_ i s not formed may mean that the well-known  order 1,5 > 1,6 >> 1,4 for rates of hydrogen a b s t r a c t i o n i n a c y c l i c systems holds f o r t h i s r i g i d system as w e l l , the preference here being a 1,5 over a 1,4 hydrogen abstraction.  2,3,4aB,56,8g,8aB-Hexamethyl-4aB ,5,8,8aB-tetrahydro-l,4-naphthoquinone.  This adduct was studied i n spite of the dismal y i e l d s  11  (<5%)  of i t s preparation because i t i s the only substrate other than 9^ which has been reported to date to undergo y~hydrogen abstraction by enone 24b carbon i n solution  .  The study of i t s s t r u c t u r e and r e a c t i v i t y i n  the s o l i d state was desirable i f for no other reason than to ensure that the s o l i d state r e a c t i v i t y of 9^ was not an i s o l a t e d case and thus provide a firmer ground f o r any conclusions which may be drawn from this reaction.  - 115 -  Compound 11 was obtained as pale yellow rods from petroleum ether as the c r y s t a l l i z i n g solvent.  I t reacted i n KBr and as the pure  s o l i d below the eutectic temperature  (60.5°) to give enone-alcohol 11A  and ene-dione 11B i n a combined i s o l a t e d y i e l d of 85%.  Of the two  photoproducts the ene-dione 11B was favored 2:1 over the enone-alcohol 11A.  The 11A:11B r a t i o was shown to be invariant at varying conversions  of the s t a r t i n g material (Table XII) which i s to be expected i n a reaction i n which both products are primary products and are photostable  Table XII.  Product Y i e l d s and Ratios f o r the 11 ->- 11A + 11B Conversion  Reaction Temperature.  % Conversion  Combined Y i e l d s 11A + 11B  11A;11B  -32.4° to -31.7°  100%  85%.  1:2  -31.6° to -27.3°  100%  86%  1:2  -32.1° to -31.5°  56%  81%  1:2  -32.0° to -30.9°  57%  95%  1:2  -31.9° to -31.6°  29%  93%  1:2  - 116  under the reaction conditions.  -  That these products are photostable  was substantiated by i r r a d i a t i n g a KBr p e l l e t containing these two primary products f o r one hour.  The recorded infrared spectrum showed  neither new peaks nor changes i n peak i n t e n s i t i e s .  Pure c r y s t a l s of  11A were also i r r a d i a t e d i n a KBr matrix f o r 2 hours.  The i n f r a r e d  spectrum of the i r r a d i a t e d p e l l e t was i d e n t i c a l to that of pure 11A. The s t r u c t u r a l assignments f o r the two products, 11A and 11B, were made on the basis of t h e i r s p e c t r a l data which were i d e n t i c a l to those reported f o r compounds of i d e n t i c a l structure i s o l a t e d from the photolysate of compound 11^ i n benzene by Scheffer and 24b coworkers The formation of these two products i s analogous to the 9_ -* 9A + j)B conversion discussed e a r l i e r . r a t i o s are comparable for the two cases.  The y i e l d s and product  By analogy to the 9.  9A + 9B  transformation, photoproduct 11A most, l i k e l y a r i s e s from the ^n,7T* state while the ene-dione photoproduct 11B most probably forms from the 3 T T , T T * state. As mentioned i n the Introduction, methyl s u b s t i t u t i o n on the ene-dione double bond and the bridgehead positions seems to be  3 required f o r the observation of the  TT,TT*  derived yhydrogen  by carbon i n t h i s series of tetrahydro-1,4-naphthoquinones.  abstraction It i s  understandable that the substitution of electron donating groups such 3 as a l k y l groups on the ene-dione double bond should lower the  TT , T T *  energy l e v e l since the promotion of a TT electron to a TT* l e v e l leaves the carbon(s) of the TT system electron d e f i c i e n t .  It i s , however, clear  - 117 -  that s u b s t i t u t i o n on the ene-dione double bond alone i s not s u f f i c i e n t for  the observation  of y-hydrogen abstraction by carbon since  substrate 24a  5_ does not undergo y-hydrogen abstraction by carbon i n solution  . It  has not yet been determined whether methyl s u b s t i t u t i o n on the bridge3  head positions alone s u f f i c e s f o r the observation The  of t h i s  Tf,Tf*  reaction.  substrate necessary to decide t h i s i s compound 12_ which cannot  be obtained by the Diels-Alder addition of 2,3-dimethylbenzoquinone to 2,3-dimethylbutadiene (which gives e x c l u s i v e l y 5_) .  Substrate 12 has  not been studied thus f a r because of t h i s synthetic problem. Substrate LL not only has the same s u b s t i t u t i o n pattern as 9^ 97 but the X-ray structure  also shows that i t has the prerequisite  geometry f o r both g-hydrogen abstraction by oxygen and y-hydrogen abstraction by carbon. The c r y s t a l structure was determined using a c r y s t a l measuring 0.30 x 0.30 x 0.70mm.  Unit c e l l and i n t e n s i t y data were  measured on a Datex-automated G.E. XRD 6 d i f f T a c t o m e t e r with Cu technique.  Unit c e l l parameters were obtained by a  least-squares  refinement of the observed 26 values of 16 r e f l e c t i o n s . The structure was solved using i n t e n s i t y data of 2051 independent r e f l e c t i o n s . Unlike the previously described X-ray structures, the structure of 1.1  - 118 -  could not be solved by d i r e c t methods  .  I t was solved by a symbolic 79  addition and tangent refinement procedure  . The f i n a l R value was  0.070. 79 C r y s t a l Data C  16 22°2' H  m o n o c l i n i c  >  space group C2/c with a=24.930(7),  b=7.795(3), c=14.472(5) A, 6 = 101.13(3)° and Z=8.  Like a l l the  tetrahydro-1,4-naphthoquinones, the molecule i s twisted such that the bridgehead groups are staggered.  Figure 23 i s a stereo diagram of  the molecule.  I  Figure 23.  Stereo diagram of substrate 11.  _ 119 .  - 120 -  As i n previous cases, the enone-alcohol product 11A a r i s e s from the abstraction of the C(8) hydrogen by 0(1) followed by bond formation between carbons 1 and 6 (Scheme 19).  I t can be seen from  the stereo diagram (Figure 23) that the C(8) hydrogen i s i n the plane of the C(1)=0(1) group.  The H to 0 separation i n the c r y s t a l i s 2.26A o  which i s a reduction of 0.21A over the corresponding distance i n substrate 9. —  I t i s , i n fact the shortest H to 0 distance observed P  i n t h i s s e r i e s of tetrahydro-l,4-naphthoquinones. This should f a c i l i t a t e g-hydrogen a b s t r a c t i o n .  Furthermore, the C ( l ) to C(6)  o  separation i s 3.33A which i s short enough f o r a van der Waals i n t e r action.  (The sum of the van der Waal's contact radius f o r the two  carbons i s 3.40A based on r ^ values compiled by Bondi  .)  Thus the  b i r a d i c a l intermediate 11'A (Scheme 19) can bond between C ( l ) and C(6) to form stable product 11A without p r i o r conformational changes. The formation of ene-dione 11B a r i s e s from the abstraction of the C5 hydrogen by carbon 2 followed by r i n g closure between C3 and C5.  The C5 hydrogen i s almost equidistant from C2 and C3, being 2.70&  from C2 and 2 . 6 6 A away from C3.  The s i t u a t i o n i s completely o  analogous to the case of molecule _9 where this'hydrogen i s 2.89A and o  2.80A, respectively from C2 and C3.  The r e l a t i v e l y shorter hydrogen to  carbon separations i n 11 should r e s u l t i n a comparatively f a s t e r abstraction process.  The comparatively shorter i r r a d i a t i o n times f o r  the complete conversion of 11. to products may be a manifestation of the nearness of both the C(8) hydrogen and the C(5) hydrogen to the  - 121 -  abstracting atoms.  As i n the case of substrate j?, the abstraction  of the C(5) hydrogen by C(3) through a five-membered t r a n s i t i o n state . i s not observed.  Photoproduct 11B a r i s e s from the abstraction of the  C(5) hydrogen by C(2).  The r e s u l t i n g b i r a d i c a l l l ' B then closes i t s  r a d i c a l centres by bonding C(3) to C(5).  The C(3) to C(5) separation  o  i n the c r y s t a l i s a short 3.17A  and so here, as i n a l l previous cases,  the b i r a d i c a l intermediate can close to product from the conformation in which i t i s formed, i . e . no conformational changes are required f o r the conversion of substrate 11 to stable photoproducts. The Geometry of the Transition State f o r B- and y -Hydrogen Abstractions 43  Ever since the p u b l i c a t i o n by McLafferty and coworkers  , of  the molecular o r b i t a l calculations on the t r a n s i t i o n state geometry for y-hydrogen abstraction i n 2-pentanone, a number of investigators have probed the geometric requirements not only f o r the McLafferty  o rearrangement  but also f o r the photochemical Norrish Type I I reaction.  In the o r i g i n a l paper c i t e d , Boer, Shannon and McLafferty examined a number of conformations f o r the six-membered c y c l i c t r a n s i t i o n state including non-planar ones and found that the energy b a r r i e r to abstraction has a minimum when the abstractable hydrogen i s i n the plane of the carbonyl group.  They c i t e d two geometries which have t h i s  arrangement:- one of these, shown below, has a l l the r i n g atoms of the six-membered t r a n s i t i o n state i n the same plane with a favorable H -0 o  distance of 1.1A but unfavorable e c l i p s i n g of the methylene hydrogens;  - 122 -  the second geometry, a non-planar one which has a l l the hydrogens staggered, i s shown below.  I t s calculated energy was roughly the  same as that of the planar one previously discussed.  conformation a l l s i x atoms of the six-membered  In t h i s l a t t e r  c y c l i c t r a n s i t i o n state  except C  are i h the same plane. With normal bond distances and p angles assumed, McLafferty and coworkers found the H -0 distance to o  o  be a considerably longer, 1.81A, compared to the 1.1A f o r the planar conformation.  Since the McLafferty rearrangement had e a r l i e r been  shown to occur only when the H -0 distance was 1.8A or less ' , 43 McLafferty and coworkers concluded that the t r a n s i t i o n state geometry  -  for y-hydrogen  123  -  abstraction was most l i k e l y planar.  What happens,  then, i n r i g i d systems where p l a n a r i t y cannot be achieved? rearrangement  s t i l l occur?  Does the  To answer these questions, Henion and  42 Kingston  investigated a bicyclononanone, -two bicyclodecanones and a  bicycloundecanone. the distance H^-0  Using Dreiding molecular models, they measured and the angle T which the approaching hydrogen makes  with the plane of the carbonyl group at the p o s i t i o n of i t s closest approach to the oxygen. ~ They then investigated t h e i r mass spectra. Their r e s u l t s are summarised i n Table XIII. Table XIII.  E f f e c t s of Structure on the McLafferty Rearrangement o  Ketone  H  to 0 distance, A  T°  Occurrence of the  —Y  McLafferty Rearrangement  - 124  "  43 In the e a r l i e r c a l c u l a t i o n s  the t r a n s i t i o n state  geometry i n which T=45° has an estimated energy which i s 76.3 above that of the planar t r a n s i t i o n state geometry. shows that while a planar six-membered r i n g may  kcal  Table XIII c l e a r l y  be the most favorable  geometry e n e r g e t i c a l l y f o r f l e x i b l e molecules, i t i s not by any means a sine qua non f o r the occurrence of the McLafferty Turning now  rearrangement.  to photochemical hydrogen abstractions, i t i s  important to note that both the Norrish Type I I reaction and McLafferty  the  rearrangement require an e l e c t r o n - d e f i c i e n t carbonyl  In the McLafferty  system.  rearrangement, t h i s i s attained by electron removal  during i o n i z a t i o n while the photochemical system r e l i e s on the promotion of an electron from an n o r b i t a l i n t o an antibonding T f * o r b i t a l . The net e f f e c t of electron promotion i s to leave an e l e c t r o n d e f i c i e n t oxygen. I t i s , therefore, not s u r p r i s i n g that the photochemical abstraction reaction has a few c h a r a c t e r i s t i c s i n common with the thermal McLafferty  rearrangement.  For example, for both reactions  y-hydrogen abstraction i s more f a c i l e f o r secondary hydrogens than for primary hydrogens.  However, there are some differences worth noting  when discussing the geometries of the activated complex f o r these reactions. 2 In the ground state, the carbonyl carbon i s sp hybridized o  and the C=0 bond length i s approximately 1.2A. In the excited s t a t e , the carbonyl carbon of formaldehyde and presumably other saturated 3 ketones and aldehydes i s sp  hybridized and the C=0  i t i s i n the ground state by about 0.  bond i s longer than  In addition, the C=0  bond  - 125 -  o f t h e e x c i t e d m o l e c u l e i s out o f p l a n e o f the C l ^ group by 27° and 35° 8 la for  t h e s i n g l e t and t r i p l e t  the  g e o m e t r i c change i s one o f a p l a n a r  n,Tf*  states respectively  Overall,  ground s t a t e m o l e c u l e  becoming p y r a m i d a l i n the e x c i t e d s t a t e . for  .  Such i s , however, not t r u e  conjugated carbonyl  compounds as r e v e a l e d by t h e s p e c t r o s c o p i c 81 s t u d i e s o f a number o f i n v e s t i g a t o r s . There a r e two important 81 consequences o f c o n j u g a t i o n . conjugation  First,  s t a b i l i z e s the planar  i t has been e s t a b l i s h e d  that  geometry r e l a t i v e t o the p y r a m i d a l  one.  F o r example, the a n a l y s e s o f t h e n , i r * a b s o r p t i o n s p e c t r a o f 81c 81d propenal and p r o p y n a l have shown t h a t t h e C-C-0 angle changes by o n l y 3° and 5 ° , r e s p e c t i v e l y , from the ground s t a t e v a l u e s . This is The  i n sharp c o n t r a s t  t o the r e p o r t e d  second e f f e c t o f c o n j u g a t i o n  change o f 20-27° f o r formaldehyde  i s t h a t e x c i t a t i o n i s no  81a  longer  81a confined  t o the c a r b o n y l  group  and b o t h t h e C=C and C=0 bonds i n  p r o p e n a l undergo bond l e n g t h e n i n g  although the l a t t e r ' s increase i s  more pronounced. F o r p r o p e n a l and p r o p y n a l t h e C=0 bond l e n g t h e n s °81c °81d by 0.08A and 0.095A r e s p e c t i v e l y as a r e s u l t o f n , T r * e x c i t a t i o n . In summary, a , B - u n s a t u r a t e d c a r b o n y l  chromophores a r e expected t o r e t a i n  t h e i r planar  e x c i t a t i o n i n contrast to t h e i r  saturated  c o n f i g u r a t i o n upon  n,Tf*  analogs which a r e p l a n a r  i n the e x c i t e d s t a t e .  i n t h e i r ground s t a t e but p y r a m i d a l  T h i s d i f f e r e n c e i n geometry has t o be borne i n  mind when d i s c u s s i n g t r a n s i t i o n s t a t e g e o m e t r i e s f o r p h o t o c h e m i c a l hydrogen a b s t r a c t i o n r e a c t i o n s . Norrish  There a r e i n d i c a t i o n s t h a t a l t h o u g h t h e  I I r e a c t i o n and the M c L a f f e r t y  rearrangement b o t h i n v o l v e t h e  '  - 126  -  a b s t r a c t i o n of a y-hydrogen v i a a six-membered t r a n s i t i o n s t a t e , two  t r a n s i t i o n s t a t e s have d i f f e r e n t g e o m e t r i e s .  the  For example, Lewis  44 and  coworkers  found t h a t b o t h endo- and  undergo the N o r r i s h  II photoelimination  exo-2-benzoylnorbornane  reaction.  Their molecular  models r e v e a l e d  t h a t the a b s t r a c t a b l e hydrogen, H^,  of the  oxygen i n the endo i s o m e r .  carbonyl  c l o s e s t approach  to 0 distance  i n the  exo  The  comes w i t h i n  1.7A  corresponding  Isomer was,  however, a  o  r e l a t i v e l y l o n g 2.2A. r e f l e c t e d by f o r the two  the ^600 substrates  Although t h i s greater  to 0 d i s t a n c e  was  f o l d d i f f e r e n c e i n the r a t e s of hydrogen a b s t r a c t i o n (equation  10 and  11),  the f a c t  t h a t the  k = 7.0  x 10  k = 1.2  x 10 sec  exo-  sec  ----(11) 7  1  - 127 -  isomer reacted at a l l shows that for photochemical hydrogen abstraction o  reactions the H -0 distance i s not limited to the 1.8A maximum e s t a Y blished for the McLafferty rearrangement. the  Perhaps a better guide for  to 0 distance requirement should be the sum of the van der .  Waals r a d i i , r , of the two atoms involved, namely, hydrogen and w  oxygen.  Van der Waals r a d i i d i f f e r widely depending on the method  of t h e i r c a l c u l a t i o n .  For instance, the van der Waals r a d i i , r, , b  o  calculated by Pauling s approximation for H and 0 are 1.06 and 1.42 A, 68 respectively  . Use of these values would give the maximum H-0 o 82 contact distance of 2.5A reported by Winnik and coworkers . However, 68 83 as pointed out by Bondi  and Edward  the "best" values for the van  der Waals r a d i i of various elements which are compatible with X-ray crystallographic data and are best suited f o r volume c a l c u l a t i o n s are those designated r .  I f one depicts the i n t e r a c t i o n between the two  atoms involved i n the abstraction reaction as two c o l l i d i n g spheres of radii  r w  (0)  and * 00 r e s p e c t i v e l y , then the contact distance between  the two atoms w i l l be the sum of these two r a d i i .  Using r (0) and w r (H) values from the recent c a l c u l a t i o n s of Bondi y i e l d s a sum of w o 2.72A.  This value represents an upper l i m i t on the distance require-  ments for the abstraction of a hydrogen by oxygen.  The lower l i m i t 84  w i l l be represented by the length of the OH bond i t s e l f  . Thus, f o r  the observation of hydrogen abstraction by oxygen, the H to 0 separation, d, must be such that 2.72A >^ d > 0.96&.  This condition i s c a l c u l a t e d  for ground state atoms but should hold for 1  n,Tr*  state hydrogen  - 128 -  abstractions by oxygen.  The abstraction involves the h a l f - f i l l e d n  o r b i t a l of oxygen which i s included i n the ground state atomic radius, r . The analogous distance requirement, d, f o r hydrogen abstraction w o o - 68 by carbon w i l l be 2.90A >_ d > 1.07A using the sum of the r for w  84 C and H f o r the upper l i m i t and the length of the C-H bond  as the  lower l i m i t . The second parameter which has been used to define the geometry of the t r a n s i t i o n state i s the angle x defined as the angle that the i t i n e r a n t H makes with the plane of the carbonyl group. This angle i s shown diagramatically below.  The H  to 0 distances and the x  values f o r the substrates found to undergo 3-hydrogen abstraction are tabulated i n Table XIV below.  Also given i n t h i s table are the H Y  distances and x' values f o r the substrates f o r which y-hydrogen  to C  - 129  abstraction by carbon was H^,0  observed.  -  For 3-hydrogen abstraction, a l l the  interatomic separations were below the s t i p u l a t e d maximum  o  Table XIV.  Interatomic Distances, Abstraction  A, and Approach Angles f o r Hydrogen  -  separation.  130  The d i s t a n c e requirement  -  i s , t h e r e f o r e , w e l l met.  Also  as t h e x v a l u e s i n d i c a t e , i n a l l cases t h e h y d r o g e n t o be a b s t r a c t e d i s a l s o i n t h e p l a n e o f t h e c a r b o n y l group,b e i n g <8° i n e v e r y c a s e .  the out of plane  angle  S u b s t r a t e 9_ a f f o r d s t h e i d e a l case, w i t h  T=0° i . e . t h e hydrogen l i e s e x a c t l y i n t h e p l a n e o f t h e c a r b o n y l group. U s i n g t h e X-ray  data f o r t h i s s u b s t r a t e  can be glimpsed about  7 7  , some i m p o r t a n t i n f o r m a t i o n  the geometry o f t h e t r a n s i t i o n  state.  The.transformation leading to the b i r a d i c a l precursor of e n o n e - a l c o h o l 9A and a l l e n o n e - a l c o h o l s , i n g e n e r a l , most  likely  i n v o l v e s t h e a b s t r a c t i o n o f one o f the C8 hydrogens by t h e h a l f - f i l l e d n - o r b i t a l of 0(1). closest  The hydrogen which i s a b s t r a c t e d i s the one which i s  to and i n the p l a n e o f  the C(1)=0(1) group.  from t h e l a c k o f e n o n e - a l c o h o l f o r m a t i o n i n i r r a d i a t e d  This i s evident c r y s t a l s o f 10  i n which t h e C(8) hydrogen i s remote and o u t o f p l a n e w i t h the C ( l ) = 0(1) to  group.  I n s u b s t r a t e 9_, atoms 0 ( 1 ) , C ( l ) , C(8a) and t h e hydrogen  be a b s t r a c t e d a l l l i e i n the same p l a n e .  calculated bond a n g l e s  The C(8) atom i s  t o be o n l y 16° above the p l a n e o f t h e s e f o u r atoms.  The  (Scheme 20) a r e a l s o i n e x c e l l e n t agreement w i t h t h e  2 3 e x p e c t e d v a l u e s o f 120° and 109.5° f o r sp and sp h y b r i d i z e d respectively.  carbon,  S i n c e t h e a n g l e f o r p l a n a r c y c l o p e n t a n e i s 108°, t h e r e  w i l l be some a n g l e s t r a i n a t the t r a n s i t i o n s t a t e i f , as i s e x p e c t e d , 2 C(l)  remains sp  transition  hybridized.  Although,  a planar cyclopentane-like  s t a t e f o r s u b s t r a t e 9_ has u n d e s i r a b l e e c l i p s i n g o f i t s  C(8a) b r i d g e h e a d m e t h y l  and the u n a b s t r a c t e d C ( 8 ) hydrogen, i t must be  - 131 -  Scheme 20  transition state  borne i n mind that t h i s s t r a i n i s present i n the substrate rather than introduced at the t r a n s i t i o n state. abstraction by carbon, the H^,,C  Turning now  to the  ybydrogen  separation, d, f o r substrates 9_ and 11  o are 2.89 and 2.66 A, r e s p e c t i v e l y .  Both distances s a t i s f y the i n t e r -  atomic separation requirement stipulated f o r t h i s reaction.  Unlike  the case of 3-hydrogen abstraction, the approach angle T deviates s i g n i f i c a n t l y from zero.  As Table XIV shows, the hydrogen  approaches  the plane of the C2, C3 double bond at angles of 50° and 52° respectively for substrates _9 and 11_.  Interestingly, t h i s i s the same as the  approach angle, x, estimated from molecular models by Henion and 42 Kingston f o r the McLafferty rearrangement  of bicyclo[5.2.1]decan-10-one  - 132  and bicyclo[5.3.1]undecan-ll-one.  -  The  only t r a n s i t i o n state  geometry compatible with the X-ray structure of substrates  9_ and  11  turns out to be a boat (Figure 24) not a c h a i r - l i k e cyclohexane r i n g 78 as suggested by Wagner and coworkers  for a c y c l i c substrates.  Since  the boat-like conformation i s forced on the t r a n s i t i o n state, no doubt,  conversion.  by the decalin r i n g structure of 9_ and  11, the p o s s i b i l i t y of a c h a i r -  l i k e t r a n s i t i o n state f o r mobile systems cannot be ruled out.  It  does mean however that the conformation of the t r a n s i t i o n state f o r these hydrogen abstraction reactions i s not required to be a s t r a i n free chair.  - 133 -  The abstraction of a y-H by carbon i n substrates 9^ and 11 most l i k e l y involves the h a l f - f i l l e d TT o r b i t a l of C(2). As mentioned 24b e a r l i e r , quenching studies  have shown the r e a c t i o n to involve a 3  t r i p l e t excited state, most l i k e l y a  Tf,Tf*.  In contrast to the  B-hydrogen abstraction discussed e a r l i e r , the hydrogen abstracted does not l i e i n theplane of the reactive chromophore, namely the C(2)=C(3) TT system.  Rather, i t approaches C(2) from above the C(2), C(3) plane  at an angle of 52°. a boat conformation.  The suggested six-membered t r a n s i t i o n  state i s i n  - 134 -  3.  Intramolecular Oxetane Formation  4a B,8ag-Dicyano-5ct,8a-dimethyl-4ag,5,8,8aB-tetrahydro-l,4naphthoquinone, 8. Well-formed, pale yellow c r y s t a l s of c r y s t a l l i z i n g from acetone-hexane.  were obtained by  I r r a d i a t i o n of 8_ both i n a KBr  matrix and as the pure s o l i d below the e u t e c t i c temperature  (123.5°)  led to the formation of 5,10-dicyano-6,9-dimethyl-ll-oxatetracyclo[6.2.1.0.^' 0^ ^^]undec-2-ene-4-one 8A as the sole product. 7  Irradia-  ,  te  t i o n of solutions of j5 also give oxetane 8A as the sole photoproduct  Ultimate proof of the product structure came from comparing i t s spectra with those of authentic 8A prepared by photolysis of 8^ i n benzene.  The X-ray structure of 8A prepared by t h i s l a t t e r method has  been determined. The 8 -> 8A conversion i s an intramolecular [ 2 —  TT  + S  2 1 TT  addition of a carbonyl f u n c t i o n a l i t y to an o l e f i n i c moiety.  S  Recent  studies on t h i s type of intramolecular photocyclization show that the reaction can occur from the  n,Tr*  s i n g l e t as w e l l as from the  TT,TT*  - 135 -  t r i p l e t depending on the intersystem crossing e f f i c i e n c y of the 28 substrate  . The i n i t i a l i n t e r a c t i o n of the excited carbonyl chromo-  phore with the i s o l a t e d double bond i s believed to y i e l d an exciplex which may eventually y i e l d an oxetane.  In order for the carbonyl  group to i n t e r a c t with the o l e f i n i c Tf system, the two TT systems must be close enough and aligned so as to have i n t e r a c t i o n between t h e i r 85 p - o r b i t a l s . Schmidt and Rabinovich found, f o r example, that short o  intermolecular C=C"''*C=C contacts of 3.49 and 3.62 A i n the two stacks of 2,5-dimethyl-p-benzoquinone and a p a r a l l e l arrangement of the two Tf-systems favored oxetane formation upon i r r a d i a t i o n . 87 X-ray structure determination was c a r r i e d out c r y s t a l of 8 measuring 0.50 x 0.30 x 0.30 mm.  on a single  U n i t - c e l l parameters  were refined by l e a s t squares from the observed 26 values of 14 46 reflections.  The structure was solved by d i r e c t methods  i n t e n s i t y data of 2419 independent r e f l e c t i o n s .  using  The f i n a l R value was  0.046. 87 Crystal Data C  14 12 2°2'  b=11.525(4),  H  N  o r t n o r n o m b i c  >  s  P  a c e  group Pbcn with a=15.915(6),  c=13.157(5) A, g=90° and Z=8. A stereo diagram of the  molecule i s shown i n Figure 25. The formation of oxetane 8A a r i s e s from a [ 2 + Tf  addition between C(1)=0(1) and C(6)=C(7).  2] c y c l o Tf  The centre-to-centre o  separation, d, of these two Tf systems i s only 3.20A which i s shorter than the intermolecular C=0 to C=C contacts encountered by Schmidt  - 136 -  F i g u r e 25.  Stereo diagram o f s u b s t r a t e J5. 85  and  Rabinovich  .  But u n l i k e t h e i r systems, the i n t r a m o l e c u l a r  and  G=C bonds i n v o l v e d i n the J3 -»• 8A c o n v e r s i o n  The o r i e n t a t i o n of these viewing  a r e not p a r a l l e l .  two d o u b l e bonds can be a p p r e c i a t e d  F i g u r e 25 through a s t e r e o v i e w e r .  OO  by  The d i r e c t i o n o f the  p - o r b i t a l s a r e a l o n g the normals t o the C(1)=0(1) and C(6)=C(7) planes.  The angle between t h e s e n o r m a l s i s 9 9 ° .  This  near-orthogonal  arrangement o f the two TT systems w h i c h i s d i a g r a m m a t i c a l l y  represented  below  formation.  ( F i g u r e 26) promotes i n t e r a c t i o n and u l t i m a t e l y bond  F i g u r e 26.  Approach geometry o f the C(1)=0 and C(6)=C(7) TT bonds.  - 137 -  The addition involves the bonding of C(l) to C(6) and 0(1) to C(7). o  These distances are 3.37 and 3.20 A r e s p e c t i v e l y i n the c r y s t a l . o  —  Using 1.70 and 1.52 A for the mean van der Waals r a d i i , r , f o r C and w  68 0 r e s p e c t i v e l y , the carbon to carbon van der Waal's contact radius o  o  i s 3.40A and that of carbon to oxygen 3.22A.  These distances are  almost exactly the distances separating the p o t e n t i a l bonding centres i n substrate _8.  Because of the favorable alignment of the  two double bonds and the short interatomic contacts the 8^ -> 8A conversion can occur without major conformational  changes.  As the  X-ray structure of 8A (Figure 27) shows, the r e a c t i o n i s attended by  - 138 "  very l i t t l e change i n the quinone r i n g and only s h i f t s i n the positions of C(6) and C(7) of the cyclohexene portion of the molecule. The X-ray data on photoproduct as i n previous structure determination. used i n the determination were 0.70  8A were obtained and treated The dimensions of the c r y s t a l  x 0.50  x 0.20 mm.  Unit-cell  parameters were obtained by least-squares refinement of the observed 29 values of 15 r e f l e c t i o n s . of i n t e n s i t y data from 1433  The structure was independent  solved from  reflections.  treatment  The f i n a l R  value was 0.048. 86 .Crystal Data ^14^12 2^2' N  o r t  h ° h b i - > space group P2^2^2^ with r  o m  c  a=18.701(6), b=7.274(2), c=9.005(2) A, 8=90° and Z=4. of the molecule c l o s e l y resembles  The geometry  that of i t s precursor 8^.  The  oxetane r i n g i s very d i s t o r t e d with a l l i n t e r n a l torsion angles greater than 30°. Intramolecular oxetane formation i n these tetrahydro-1,4naphthoquinones seems to be a l e s s preferred reaction than the c y c l o butane forming dimerization and the hydrogen abstraction reactions because a l l the substrates studied have roughly the same o r i e n t a t i o n of the C(1)=0(1) and C(6)=C(7) double bonds as does 8 and i n addition have short contacts between these bonds (Table XV) and yet oxetane formation did not compete with either the dimerization or the hydrogen 88 abstraction reactions. Arnold  has noted a s i m i l a r trend e a r l i e r .  - 139 Table XV.  Intramolecular Bond Contacts and Orientation Intramolecular C(1)=0(1) ...C(6)=C(7) contact, A (centre to centre)  Substrate  a  ;  U 3.37  . =  o  06. DO),  M  a  c  Angle between normals to the C=0 and C=C planes (angle between the p orbital)  IN cM  92.4°  -  ]  3.35 (Type A) 3.40 (Type B)  90.3°(Type A) 88.5°(Type B)  3.45  87.1°  3.41  89.5°  3.39  89.8°  3.26  97.3°  3.20  99.2°  3.29  95.1°  3.38  91.8°  0  0 0  i (  - 140 -  He finds that,  i n general, whenever a hydrogen i s e a s i l y accessible  to an excited carbonyl group, hydrogen abstraction becomes so important as to exclude oxetane formation. Substrates 8_ and 1^ are two substrates which one might expect to undergo the Norrish Type II reaction since they have abstractable y-hydrogens.  Substrate 1 did undergo the Type II reaction i n  solution but not i n the s o l i d state because favorable  intermolecular  contacts i n the c r y s t a l l i n e state permitted a much preferred dimerization to occur.  With unfavorable intermolecular contacts,  j3 might be expected to undergo the Type II r e a c t i o n ,  substrate  especially o  since the y-hydrogen to oxygen distance i s only 2.41A which compares o  favorably with H^O distances of 2.58A or l e s s for the observance of hydrogen abstractions discussed e a r l i e r .  However, i n order for a  substrate to give stable products a r i s i n g from hydrogen abstraction, i t has to be able to not only abstract the hydrogen but also close i t s r a d i c a l centres.  For substrate 8^ t h i s means forming a bond  between carbons 3 and 9 i n the b i r a d i c a l 8'B without gross changes o  i n conformation.  These centres are >4A apart i n the c r y s t a l of 8_.  - 141 "  Thus, Norrish Type II products cannot form from the conformations i n which these tetrahydro-l,4-naphthoquinones c r y s t a l l i z e .  The  formation of the Type II product 1B_ during the s o l u t i o n photochemistry of 1 must then be seen as a manifestation of b i r a d i c a l  IB's a b i l i t y  to change conformation to one which permits r i n g closure between carbon centres 3 and 9.  For b i r a d i c a l 8'B the change from i t s  o r i g i n a l conformation to one such as shown below> which permits C3 to C9 bonding, requires that the bridgehead cyano groups be moved,  f i r s t , towards each other, then be eclipsed and f i n a l l y past each other.  The f i n a l conformation i s , probably, as good as the i n i t i a l  one but the process of attaining i t i s e n e r g e t i c a l l y unfavorable  - 142  -  because of dipole-dipole repulsion between the cyano groups.  So  the difference i n r e a c t i v i t y between jL_ and 8^ i n s o l u t i o n i s most l i k e l y due to the a b i l i t y of b i r a d i c a l l'B and not 8'B to change conformation.  -  4.  143  -  Unreactive Substrates  2,3,6,7-Tetramethyl-4a8, 5,8,836 -tetrahydro-1,4-naphthoquinone, Jj  Colorless needles of t h i s compound were obtained by c r y s t a l l i z i n g from petroleum-ether.  One of these c r y s t a l s measuring  0.25 x 0.10 x 0.10 mm was used f o r X-ray structure determination. Unit c e l l parameters were obtained by least-squares refinement of the observed 20 values of 19 r e f l e c t i o n s .  The structure was solved  using intensity data of 2442 independent r e f l e c t i o n s .  The f i n a l R  value was 0.072. 89 Crystal Data ^14^18^2'  m o n o c  li i > n  c  space group P2^/c with a=5.245(2),  b=29.452(7), c=8.278(5) A, 3=106.44(4)° and Z=4. the molecule i s shown i n Figure 28.  Figure 28.  Stereo diagram of substrate 5_.  A stereo view of  - 144 -  I r r a d i a t i o n of c r y s t a l s of 5_ e i t h e r i n a KBr matrix or as the pure s o l i d i n vacuo l e d to no detectable r e a c t i o n .  In solution,  however, t h i s substrate i s reported to give photoproducts 5A and 5_B  fsolid state *  N  o  r  e  a  c  t  i  o  n  requirements to undergo 8-hydrogen abstraction.  The 0(1) to Hg  o  o  distance i s 2.42A and the C ( l ) to C(6) separation i s 3.49A.  So,  one would expect 0(1) to abstract Hg upon UV i r r a d i a t i o n with subsequent bond formation between C ( l ) and C(6) to give 5A.  enone-alcohol  As i n previous examples, photoproduct 5Ji i s not expected to form  i n the i r r a d i a t i o n of 5_ i n the s o l i d state.  The inertness of 5_ to  i r r a d i a t i o n i s p a r t i c u l a r l y s u r p r i s i n g since compound 4_ i n which the Hg to 0(1) distance i s 2.46A and the C ( l ) to C(6) separation was  - 145 -  o  3.51A d i d r e a c t t o g i v e the expected  enone-alcohol.  These  inter-  a t o m i c s e p a r a t i o n s a r e almost e x a c t l y e q u a l t o t h e Hg t o 0 ( 1 ) and C(l) for  t o C(6) s e p a r a t i o n s i n s u b s t r a t e 5_.  A possible explanation  _5_'s i n e r t n e s s r e s i d e s i n the c r y s t a l p a c k i n g .  two a d j a c e n t m o l e c u l e s  F i g u r e 29 shows  within a crystallographic c e l l .  !•  '  F i g u r e 29.  Two a d j a c e n t m o l e c u l e s  c a r b o n y l group  o f 5_ w i t h i n a c r y s t a l l o g r a p h i c c e l l .  The a n g l e between t h e normals t o t h e  p l a n e s o f t h e two c a r b o n y l groups i s o n l y 16.4°.  So t h e y a r e almost  a p a r a l l e l o r i e n t a t i o n and the two TT systems s h o u l d  provided  1  o f one m o l e c u l e l i e s above t h e C ( 4 ) - 0 ( 2 ) c a r b o n y l  group o f a second m o l e c u l e .  in  The C(1)=0(1)  they a r e c l o s e enough t o each o t h e r .  interact  The c e n t r e - t o - c e n t r e o  double bond s e p a r a t i o n f o r these two c a r b o n y l groups i s 3.65A which i s c e r t a i n t o promote a s t r o n g i n t e r a c t i o n between t h e s e two chromophores. Of t h e two c a r b o n y l groups o n l y C(1)=0(1) i s c o n f o r m a t i o n a l l y  capable  - 146 -  of B-hydrogen abstraction upon i r r a d i a t i o n . From a c r y s t a l l o g r a p h i c viewpoint, there are two possible reasons f o r the p h o t o s t a b i l i t y of 5_ i n the s o l i d state but not i n solution. separation  The short  intermolecular  of the two carbonyl groups may be giving r i s e to (I)  exciton migration and self-quenching  and/or ( i i ) an i n t e r a c t i o n  between an excited molecule and an unexcited neighbour giving r i s e to an excimer which subsequently decays and d i s s o c i a t e s to two ground state molecules.  In connection with the f i r s t of these two p o s s i b i -  l i t i e s , i t has already been mentioned i n the Introduction  that both  singlet and t r i p l e t migrations are known to occur i n c r y s t a l s and the wandering of the t r i p l e t i s usually more extensive than that of the s i n g l e t p a r t l y as a r e s u l t of the longer l i f e t i m e of the t r i p l e t state.  During migration,  the e x c i t a t i o n energy i s frequently  scattered by l a t t i c e v i b r a t i o n s u n t i l i t decays o p t i c a l l y or thermally. In addition, migration also promotes the i n t e r a c t i o n between two excitons.  The i n t e r a c t i o n can be between two s i n g l e t excitons or  two t r i p l e t excitons,  the l a t t e r i n t e r a c t i o n i s more frequently  encountered than the former again because the t r i p l e t state l i v e s longer, wanders more extensively and, therefore, has more p r o b a b i l i t y of i n t e r a c t i n g with another t r i p l e t exciton than the s i n g l e t . this intermolecular  During  exciton i n t e r a c t i o n , one member of the p a i r  comes o f f with a higher e x c i t a t i o n energy than i t i n i t i a l l y the other molecule i s deexcited  to the ground-state.  had and  The e l e c t r o n i c  energy of the excited partner i s usually l e s s than the combined energies of the two excited states since some of the e l e c t r o n i c energy  -  147  -  i s l o s t to the l a t t i c e as heat during the i n t e r a c t i o n .  The process  90 i s known as s i n g l e t - s i n g l e t a n n i h i l a t i o n  when the excitons  are s i n g l e t s and referred to as t r i p l e t - t r i p l e t a n n i h i l a t i o n two t r i p l e t s are involved.  The 'new' excitons,  involved 90 when  and T.. (Scheme 21)  cascade down to the lowest s i n g l e t which may continue i t s migration Scheme 21 2  s  r  S J  ±  + S  + heat ( s i n g l e t - s i n g l e t  q  <10" sec 6  S  S  o  D  + heat  + hv  annihilation)  - 148  till  -  another a n n i h i l a t i o n s e t s i n o r u n t i l  l o s e s i t s e x c i t a t i o n energy.  i t thermally or  In the quenching o f  optically  irradiated  21 c r y s t a l s o f 5_, h o s t - s e n s i t i z a t i o n  i n w h i c h the l a t t i c e  rather  than i m p u r i t i e s p l a y the major r o l e o f t r a n s m i t t i n g the e x c i t a t i o n energy from one  p a r t of the c r y s t a l to a n o t h e r , i s most l i k e l y t o  the key d e a c t i v a t i o n pathway. d i s l o c a t i o n s and The  the p o s s i b i l i t i e s  of  i m p u r i t i e s a l s o p l a y i n g a r o l e cannot be r u l e d out.  second p o s s i b l e major p a t h  o r a-bond formation and e x c i t e d m o l e c u l e and may  Nevertheless,  be  f o r d e a c t i v a t i o n , namely, excimer  decay r e q u i r e s an a s s o c i a t i o n between one  unexcited  not e n t a i l a bond f o r m a t i o n  molecule.  The  between the two  one  i n t e r a c t i o n , may  partners.  In  or  the  case where the i n t e r a c t i o n does not e n t a i l bond f o r m a t i o n ,  the  e x c i t e d s p e c i e s w i l l resemble an i n t e r m o l e c u l a r e x c i p l e x .  Since  the  i n t e r m o l e c u l a r C(1)=0(1) to C(4)=0(2) d i s t a n c e o f 3.65A i n 5_ i s o  almost e q u a l  to the 3.62A c o n t a c t  oxetane f o r m a t i o n  o f C=0  to C=C  which 85  i n 2,5-dimethyl-p-benzoquinone  of a 1,3-dioxetane as a t r a n s i e n t i n t e r m e d i a t e o f c r y s t a l s of 5_ i s a t l e a s t have been r e p o r t e d  conceivable.  i n the l i t e r a t u r e .  as a t r a n s i e n t i n t e r m e d i a t e  f o l l o w e d by  permitted  , the  formation  d u r i n g the  To d a t e , no  irradiation  1,3-dioxetanes  Nonetheless, i t s formation f a c i l e d e c o m p o s i t i o n to  two  c a r b o n y l fragments would c l o s e l y p a r a l l e l the b e h a v i o u r o f known  * 1,2-dioxetanes. it  So t h a t , whatever the n a t u r e  r e a d i l y decays t h e r m a l l y o r p h o t o c h e m i c a l l y  molecules.  o f the excimer, t o two  (S^S^) ,  ground s t a t e  T h i s second mode o f d e a c t i v a t i o n o f e x c i t e d m o l e c u l e s o f  149 -  5_ i n the s o l i d state i s summarised i n Scheme 22 where SQ denotes the substrate 5_ i n i t s ground state and S ^ denotes _5 i n i t s f i r s t excited state.  Scheme 22  sQ  s,  a _  [  S  q  S  i  2S  Q  + hv'  2S  Q  + heat  ]  . excimer  2,3,4ag,5a,8a,8ag-^Hexamethyl-4ag,5,8,8ag-tetrahydro-l,4-naphthoquinone. 10 This adduct c r y s t a l l i z e d out of hexane as low melting rods (mp 52-54°).  The X-ray structure of t h i s molecule i s not yet a v a i l a b l e .  Nevertheless, i t s behaviour under UV i r r a d i a t i o n i n the s o l i d state 24b was studied because i t was reported  to give photolabile oxetane  1QA and the caged compound 10B when i r r a d i a t e d i n s o l u t i o n .  Given  the conformation i n which a l l the tetrahydronaphthoquinones so f a r  - 150 -  s t u d i e d c r y s t a l l i z e , one does n o t expect 10B t o be formed i n a lattice-controlled  solid  s t a t e r e a c t i o n , b u t 10A might be e x p e c t e d  to form by a n a l o g y t o the {$  8A  conversion previously  described.  I r r a d i a t i o n o f 10 i n a KBr m a t r i x gave no r e a c t i o n i n up t o 2 hours of i r r a d i a t i o n .  I n the i n f r a r e d  spectrum r e c o r d e d a f t e r 6 hours o f  i r r a d i a t i o n , b r o a d e n i n g i n t h e 5.67-5.78 y r e g i o n was o b s e r v e d . A f t e r 17 hours two new c a r b o n y l a b s o r p t i o n s a t 5.70 and 5.76 y became prominent.  These a b s o r p t i o n s c o u l d be due t o t h e caged 24b  isomer, t h e c a r b o n y l a b s o r p t i o n s o f which have been r e p o r t e d 5.68 and 5.75 y. i n the i n f r a r e d  Oxetane  at  10A c o u l d a l s o be p r e s e n t b u t u n d e t e c t e d  s i n c e i t s c a r b o n y l a b s o r p t i o n a t 6.04y  w i t h t h e a b s o r p t i o n o f r e s i d u a l 10 a t 6.00y.  The l o n g  coincides induction  p e r i o d f o r t h e appearance o f t h e s e p r o d u c t ( s ) and t h e f a c t  t h a t the  KBr p e l l e t was i r r a d i a t e d a t room temperature w i t h no p r o v i s i o n f o r preventing the p e l l e t  from h e a t i n g up s t r o n g l y s u g g e s t e d t h a t t h e  r e a c t i o n was o c c u r r i n g from t h e m e l t and n o t from t h e s o l i d .  To  f u r t h e r s u b s t a n t i a t e t h i s , pure c r y s t a l s o f 10_ were i r r a d i a t e d i n vacuo a t lower and c o n t r o l l e d solid.  temperatures t o e n s u r e t h a t i t s t a y e d  I r r a d i a t i o n a t 0.03 t o r r a t temperatures between -9.9° and  -9.1° f o r 14 hours gave 95% o f r e c o v e r e d m a t e r i a l which was shown by t h i n l a y e r chromatography,  i n f r a r e d and NMR  hv  solid  10  state  t o be i d e n t i c a l t o t h e  No  reaction  - 151 -  starting material 10.  Another t r i a l run at 0.03 t o r r and s l i g h t l y  higher temperatures (-1.4° to -0.5°) f o r 13 hours also l e d to no reaction. As mentioned e a r l i e r , the  4a,5,8,8a-cis-tetrahydro-l,4-  naphthoquinones which have thus f a r been studied seem to prefer cyclobutane r i n g forming dimerization and hydrogen abstraction to intramolecular oxetane formation. 8^ -* 8A conversion,  But as has been shown by the  when none of these preferred reactions i s p o s s i b l e ,  oxetane formation can be observed.  The formation of oxetane 10A i n  solution but not i n the s o l i d state may mean that excited 1(3 c r y s t a l s have some e f f i c i e n t means of deactivating to ground state which the molecules i n s o l u t i o n do not have.  But without the X-ray structure,  i t cannot be ascertained whether t h i s i s a c r y s t a l packing e f f e c t as i n the case of substrate 5_ or some other conditions p e c u l i a r to the crystalline  state.  In summary, the four r e a c t i o n types encountered during UV i r radiation of a number of tetrahydro-1,4-naphthoquinones i n the s o l i d state can be r a t i o n a l i s e d i n terms of the p r i n c i p l e of least motion also known as the topochemical p r i n c i p l e " ^ '^~ . >  elaborated  on t h i s p r i n c i p l e .  Cohen"^ has recently 3  He defined a "reaction c a v i t y " as  the space occupied by a reactant molecule or molecules as the case may be.  The s i z e and shape of t h i s c a v i t y i s determined by the  structure and geometry of the molecules of the substrate(s).  The  topochemical p r i n c i p l e i s then interpreted to mean that a l a t t i c e controlled transformation  proceeds with minimal d i s t o r t i o n of the  -  surface of the reaction cavity.  152  -  Within-this i n t e r p r e t a t i o n ,  extrusions from the c a v i t y as w e l l as the c r e a t i o n of voids w i t h i n the cavity as a r e s u l t of a reaction are e n e r g e t i c a l l y unfavorable. Figure 30 i s a diagramatic representation of a favorable and unfavorable s o l i d state transformation.  Figure 30.  As reaction proceeds a point i s  The r e a c t i o n cavity before r e a c t i o n ( f u l l l i n e ) and i n the t r a n s i t i o n state (broken l i n e ) f o r energetically a) favorable process, b) unfavorable process.  reached when the r e s t r i c t i o n s imposed on the conformation of product molecules i s relaxed and the l a t t e r then c r y s t a l l i z e out i n t h e i r own conformation.  But u n t i l t h i s stage i s reached, products which  have shapes most resembling those of reactant molecules or a l t e r n a t i v e l y those with r e a d i l y deformable accommodated by the host l a t t i c e .  structures w i l l be e a s i l y  The i d e a l s o l i d state transformation  w i l l be one which y i e l d s a product which i s c r y s t a l l o g r a p h i c a l l y ~ isomorphous with the s t a r t i n g material.  Such reactions should  - 153 -  proceed e s s e n t i a l l y to completion without any d i s t o r t i o n of the 91 crystal lattice.  Wegner and coworkers  reported one such s o l i d  state reaction. In the reactions presented  i n t h i s p u b l i c a t i o n , i t has been  shown c o n s i s t e n t l y from the X-ray data of the substrates that the t r a n s i t i o n state could be reached with hardly any change i n the conformation of the substrate.  Furthermore, i t has been shown that  only stable products which can be formed without major changes i n the substrates' conformations do form i n the s o l i d state reactions. This conformational  c o n t r o l has permitted  the estimation  of c e r t a i n useful reaction parameters;a) The cyclobutane  r i n g forming [^2^ + ^2 ] dimerization  has been shown to occur from a centre-to-centre double bond o  separation, d, of 4.04A or less and the two double bonds approach each other i n a p a r a l l e l o r i e n t a t i o n which allows f o r maximum overlap of t h e i r p - o r b i t a l s . The s i t u a t i o n here i s completely analogous to 12 59 the dimerization of a-cinnamic a c i d c r y s t a l s ' b) Intramolecular oxetane formation has been observed at o  a centre-to-centre C=0  to C=C  separation, d, of 3.20A.  The approach  of the two double bonds i s such that the p - o r b i t a l s are almost at r i g h t angles. for overlap.  This near-orthogonal  approach i s also a good geometry  The distance separating the two double bonds i s short  compared to the corresponding  separation i n intermolecular oxetane 85 forming reactions reported by Schmidt and coworkers . The short  -  154.-  contact would tend to promote a stronger  i n t e r a c t i o n and  ultimately  r i n g closure. c) The abstraction of a hydrogen $ to a carbonyl  group by  the carbonyl oxygen has been shown to occur from a distance ranging from 2.26A to 2.58A. d) The  abstraction of a y-hydrogen by the carbon of an o  excited enone system occurred respectively i n two  o  from distances of 2.66A and 2.89A  substrates.  The longer separation between the  abstractable hydrogen and the abstracting atom here as compared to  (c)  above i s a r e f l e c t i o n of the larger van der Waals volume of carbon r e l a t i v e to that of oxygen.  In both types of hydrogen abstraction,  the 0 to H and C to H separations were l e s s than or equal to the sum of the van der Waals r a d i i of the two atoms involved i n the abstraction. The retention of gross conformation during the has also made i t possible to define the geometry of the state more p r e c i s e l y than has hitherto been.possible.  abstractions transition The  abstraction  of a hydrogen 8 to an excited carbonyl group by the carbonyl oxygen has been shown to occur through a planar five-membered t r a n s i t i o n state.  The corresponding abstraction of y~hydrogen by carbon of an  excited enone chromophore has a non-planar six-membered c y c l i c t r a n s i t i o n state which i s , however, not i n the t o r s i o n - f r e e chair 43 conformation proposed by McLafferty boat-shaped conformation.  and coworkers  but rather i n a  - 155 i  Overall, intermolecular e f f e c t s have been found to play an important r o l e i n the photochemical behaviour of c r y s t a l s of the tetrahydro-l,4-naphthoquinones studied only when intermolecular contact between unsaturated  centres i n adjacent molecules i s  o  <4.04A.  When this distance i s exceeded, intramolecular  processes  predominate. L a s t l y , the p o s s i b i l i t y of d i s l o c a t i o n s and/or defects playing a r o l e i n some of these systems cannot be  overlooked  especially i n the 3^ -> J3B conversion and i n explaining the behaviour of substrates 5_ and IJ) i n the s o l i d state. After the commencement of the investigations presented  here,  a report on gold-catalysed rearrangement of s t r a i n e d small r i n g  92 hydrocarbons appeared i n the l i t e r a t u r e  .  There i s no i n d i c a t i o n ,  however, that the gold metal surface on which the c r y s t a l s of were studied catalysed any of the reactions observed.  1-11  This  conclusion i s based on the fact that a l l the reactions studied i n the reactor were also studied i n KBr matrices. each compound by both methods was  identical.  The r e a c t i v i t y of  -  156  -  EXPERIMENTAL  General  Eutectic  Temperature  Eutectic analyses  (DTA) u s i n g a P e r k i n Elmer DSC-IB.  following  was  i ) crude r e a c t i o n  In each c a s e , the  i n t o a f i n e powder.  a c c o m p l i s h e d by d i s s o l v i n g  Each e u t e c t i c  was  the m i x t u r e i n a c e t o n e o r c h l o r o f o r m ,  used ranged from 5 t o 10 m i l l i g r a m s .  The sample was  Sample  sizes  p l a c e d i n an  aluminum p l a n c h e t t e and c o v e r e d w i t h an aluminum l i d .  The l i d was  mixture  In c e r t a i n c a s e s , thorough m i x i n g  the s o l v e n t and d r y i n g the sample i n vacuo.  a c c e s s o r i e s are a v a i l a b l e  was  m i x t u r e , i i ) v a r y i n g c o m p o s i t i o n s o f crude  m i x t u r e and added s t a r t i n g m a t e r i a l .  ground  removing  thermal  m i x t u r e s were a n a l y s e d u n t i l a sharp m e l t i n g t r a n s i t i o n  observed: reaction  temperatures were d e t e r m i n e d by d i f f e r e n t i a l  Both o f t h e s e  as P e r k i n Elmer Sample Pan K i t No.  219-0041.  f i r m l y p r e s s e d a g a i n s t the sample w i t h o u t c r u m p l i n g o r  c r e a s i n g the l i d . temperature was  Scanning f o r e u t e c t i c  t r a n s i t i o n s above  c a r r i e d out a t a s l o p e s e t t i n g o f 510,  a  ambient  differential  temperature s e t t i n g o f 485, an average temperature s e t t i n g o f 522 a s c a n n i n g r a t e o f 10°/min.  Low  and  temperature t r a n s i t i o n s were determined  at s l o p e s e t t i n g 500, d i f f e r e n t i a l  temperature s e t t i n g 491,  average  - 157 -  temperature  s e t t i n g 430 and a scanning r a t e of 5°/min.  A transition  was recorded as the f i r s t departure from base l i n e i . e . at the, beginning of a peak.  Low temperature  t r a n s i t i o n s were corrected  using a c a l i b r a t i o n graph obtained by scanning f o r the melting t r a n s i t i o n s of n-octane (m.p. A l l other temperature  -56.8°) and ethylene g l y c o l (m.p.  read-outs were corrected using a c a l i b r a t i o n  graph obtained by scanning melting point standard samples. c a l i b r a t i o n was  -11.5°).  Each  c a r r i e d out at the appropriate instrumental settings  c i t e d above.  Melting point (m.p.) A l l melting points except those indicated by asterisk(s) were taken on a Fischer-Johns hot stage melting apparatus and are uncorrected.  Melting point* (m.p.*) The melting point of a compound found to melt at about ambient temperature  was determined by sealing the sample i n a c a p i l l a r y  tube, then repeatedly freezing i t i n l i q u i d nitrogen and thawing i t t i l l the walls of the tube became evenly coated with the s o l i d . c a p i l l a r y tube was  then immersed i n a s t i r r e d dry ice-acetone mixture  which was consequently allowed to warm to room temperature. thermometer which had been calibrated against a  graph.  The reported m.p.*  An alcohol  copper-constantan  thermocouple i n the region 20° to -40° was used to note the of melting.  The  temperature  was corrected using the c a l i b r a t i o n  - 158 -  M e l t i n g p o i n t * * (m.p.**) The m e l t i n g p o i n t s o f compounds w h i c h decompose d u r i n g normal m e l t i n g p o i n t d e t e r m i n a t i o n s were c a r r i e d o u t by t h e DTA method.  Instrumental s e t t i n g s reported f o r e u t e c t i c  d e t e r m i n a t i o n s above ambient temperature  were  temperature  used.  Infrared All  infrared  457 s p e c t r o p h o t o m e t e r .  s p e c t r a were r e c o r d e d on a  Perkin-Elmer  F o r s o l i d s , KBr p e l l e t s c o n t a i n i n g 1-2 mg o f  the sample p e r 250 mg o f KBr were made u s i n g a P e r k i n - E l m e r Bromide Evacuable  D i e 186-0002 and a Carver L a b o r a t o r y P r e s s Model B.  The p r e s s i n g l o a d was g e n e r a l l y 20,000 l b s p e r square Infrared  s p e c t r a o f l i q u i d s were r e c o r d e d  N u c l e a r Magnetic  Potassium  Resonance  inch.  neat.  (NMR)  S p e c t r a o f s t a r t i n g m a t e r i a l s 1-11 and q u a n t i t a t i v e a n a l y s e s were taken on a V a r i a n T-60 i n s t r u m e n t of photoproducts  Spectra  1A-11B were r e c o r d e d on e i t h e r a V a r i a n HA-100 o r  XL-100 by the d e p a r t m e n t a l Chan.  by t h e a u t h o r .  NMR  s p e c t r o s c o p i s t s , Mr. W.B.  Lee and Dr. 0.  In a l l c a s e s , t e t r a m e t h y l s i l a n e (TMS) was added as an i n t e r n a l  standard.  93 Q u a n t i t a t i v e NMR A n a l y s i s T h i s was t h e method o f c h o i c e f o r t h e d e t e r m i n a t i o n o f t h e e x t e n t o f r e a c t i o n f o r compounds which d i d n o t come o f f t h e GLC columns tried.  - 159 -  An a l i q u o t , usually 0.3 ml, of a standard s o l u t i o n containing 228.3 mg of CH N0 3  2  per 10.0 ml of CVCl^ s o l u t i o n was  added  to an accurately weighed reaction mixture using a 2 ml pipette graduated i n 0.01 ml.  Sample sizes used ranged from 32.5 to 101.0  to ensure good s i g n a l to noise r a t i o . dissolve.  mg  The mixture was shaken w e l l to  The solution was transferred into an NMR  tube.  The sample  v i a l was washed with a few drops of CDCl^ and the washings added to the contents of the NMR  tube.  The resonance used i n each analysis was  well resolved and removed f rom other resonances.  The chosen resonance  used i n each such analysis i s indicated i n the Experimental.  This  chosen resonance and that of the i n t e r n a l standard were e l e c t r o n i c a l l y integrated 4 times. Since the H s i g n a l strength i s proportional to the number of magnetic n u c l e i  93  , the sample's chosen resonance strength, x, i s  given by  x °=  and that of the i n t e r n a l standard's resonance i s given by  b  whence  x y  w,s w  a b  s  _ _M ' M„  - 160 -  and  where  w  w  s  s  b M  = milligrams of r e s i d u a l s t a r t i n g material present i n the NMR mixture molecular weight of s t a r t i n g material  a  g  = no. of protons i n the integrated resonance of the s t a r t i n g material  b  = no. of protons i n the integrated resonance of the i n t e r n a l standard  (=3 f o r CH N0 ) 3  2  M  = molecular weight of the i n t e r n a l standard  (=61.04)  w  = milligrams of i n t e r n a l standard  x  = average e l e c t r o n i c i n t e g r a t i o n of the compound's  i n the NMR sample  resonance y  = average e l e c t r o n i c i n t e g r a t i o n of the i n t e r n a l standard's resonance  The extent of reaction = % conversion =  where  W  W-w  8  W"  = weight of the reaction mixture used i n the a n a l y s i s .  In the case of the reaction of compound 6_, where none of the resonances of the s t a r t i n g material were w e l l resolved from the product resonances, a well resolved resonance of the product,  - 161 -  6A, was used instead.  In t h i s case, the s u b s t i t u t i o n ,  milligrams of product 6A i n the NMR  was made into equation  (1).  sample =  W-w  s  This equality was v a l i d i n t h i s case  because the consumption of 6^ resulted i n the production of only  6A.  Mass Spectra A l l mass spectra reported i n t h i s work are low r e s o l u t i o n spectra obtained on a d i r e c t i n l e t Varian A t l a s MAT at  70eV and operated by the departmental  Mr. G.D.  Elemental  CH 4-B or AEI  MS-9  analysts, Dr. G. Eigendorf,  Gunn and Mr. J . Nip.  Analyses Elemental analyses were performed by the  departmental  microanalyst, Mr. P. Borda. Thin Layer Chromatography  (TLC)  Thin layer chromatography c a r r i e d out f o r a n a l y t i c a l purposes was done on s t r i p s of aluminum-backed s i l i c a gel 60F-254 (thickness 0.2  to 0.25  mm)  a v a i l a b l e from E. Merck.  The  solvent used i n each instance i s indicated i n parentheses i n the Experimental.  Preparative TLC was  developing elsewhere  c a r r i e d out on 20x20 cm  glass plates coated with s i l i c a gel GF-254 (thickness 0.7 which had been dried i n a i r and then at 45-50° overnight.  to 0.8  mm)  - 162 -  Column Chromatography Two  t y p e s o f a d s o r b e n t s were used:  silica  g e l 60  (particle  s i z e l e s s t h a n 0.063 mm)  from E. Merck and Woelm's n e u t r a l aluminum  o x i d e a c t i v i t y grade 1.  The a d s o r b e n t and e l u e n t used i n each i n s t a n c e  are i n d i c a t e d i n parentheses.  Gas L i q u i d  Chromatography GLC  90-P  s e p a r a t i o n s were c a r r i e d out on e i t h e r V a r i a n Aerograph  o r a V a r i a n Autoprep  E l e c t r o n i k 15 s t r i p was  helium.  temperature  (GLC)  The  A-700 i n s t r u m e n t s c o n n e c t e d  chart recorders.  to  Honeywell  The c a r r i e r gas i n a l l cases  column s i z e and p a c k i n g m a t e r i a l as w e l l as the column  and h e l i u m f l o w r a t e through the column a r e i n d i c a t e d i n  p a r e n t h e s e s where a p p l i c a b l e .  Q u a n t i t a t i v e GLC  Analysis  Peak a r e a s used i n c a l c u l a t i o n s r e p r e s e n t averages o f peak a r e a s measured f o r f o u r o r more i n j e c t i o n s .  D e t e c t o r Response F a c t o r , k: The d e t e c t o r response f a c t o r , k, f o r a compound, X, determined  by a n a l y s i n g a s o l u t i o n c o n t a i n i n g an a c c u r a t e l y weighed  amount o f X and an a l i q u o t o f a s t a n d a r d s t o c k s o l u t i o n o f an standard.  was  Peak a r e a s were c a l c u l a t e d u s i n g the f o r m u l a  A r e a = (peak w i d t h at h a l f - h e i g h t ) x (height) .  The d e t e c t o r r e s p o n s e  f a c t o r i s then g i v e n by  internal  _ 163 _  K  =  • w  where  w  s  —  Ax  x  = weight of compound x  s  = weight of i n t e r n a l standard  w  A  s  = average peak area of i n t e r n a l standard  A  x  = average peak area of compound x  Weight Calculations: The analysis of a reaction mixture consisted of adding an aliquot of the same i n t e r n a l standard s o l u t i o n as that used f o r the detector response f a c t o r determination, to a weighed amount of the reaction mixture.  The r e s u l t i n g solution was then analysed by GLC.  The weight of a component, w^, i n the solution i s given by the equation i w± = w k — s A  s  where  w  s  (2)  ± A  = weight of the i n t e r n a l standard used  k-j^ = the detector response factor f o r component i Aj[ = average peak area f o r component i A  s  = average peak area for the i n t e r n a l standard  Using equation (2) the weight of residual s t a r t i n g material mixture was calculated.  As i n the case of the NMR  W - w % conversion = — — W where and  i n a reaction  analysis  s  W = weight of the reaction mixture used i n the analysis * w  s  = weight of r e s i d u a l s t a r t i n g material  i n the mixture .  -  164  -  Solvents All  s o l v e n t s were d i s t i l l e d  Unless otherwise i n d i c a t e d , boiling  t h r o u g h a f r a c t i o n a t i n g column.  t h e p e t r o l e u m e t h e r used was the f r a c t i o n  >68°.  O p t i c a l R o t a t i o n s , a, f o r E n o n e - a l c o h o l TA were t a k e n on a P e r k i n Elmer 141 P o l a r i m e t e r o p e r a t e d a t t h e sodium D l i n e  (589 nm).  Single  c r y s t a l s f o r t h i s purpose were grown from a c e t o n e - p e t r o l e u m e t h e r and checked under a p o l a r i z i n g m i c r o s c o p e t o determine which were s i n g l e and which were twinned o r c l u s t e r e d . ranged from 2.4 t o 8.7 mg.  Crystal  crystals sizes  A s o l u t i o n o f known c o n c e n t r a t i o n was  made up by d i s s o l v i n g a weighted s i n g l e c r y s t a l i n d i s t i l l e d to make 1.0 ml o f s o l u t i o n .  acetone  A one-decimeter c e l l h o l d i n g ^0.8 ml  of s o l u t i o n was f i l l e d w i t h pure acetone and used t o z e r o t h e i n s t r u m e n t . The c e l l was then f i l l e d a,  read.  w i t h t h e sample s o l u t i o n and t h e r o t a t i o n ,  F o r each sample,  f o u r r e a d i n g s were made, and t h e average  r e a d i n g used i n the c a l c u l a t i o n below. noted,  The temperature was a l s o  a was a l s o determined f o r a c l u s t e r o f c r y s t a l s (11.9 mg).  Specific rotations,  [a]  t°  , r e p o r t e d were c a l c u l a t e d  from t h e e q u a t i o n  below:  [a]  where  a  1-c  a  the o b s e r v e d r o t a t i o n a t A=589 nm and t=25.5°  1  the  cell  c  the  c o n c e n t r a t i o n o f the s o l u t i o n i n grams p e r ml o f  solution.  l e n g t h i n d e c i m e t e r s (=1)  Figure 31.  Apparatus for Irradiations i n the Solid State. into Part B.  (a) Part A;  (b) Part A being inserted  Figure 31(c).  The Assembled  Apparatus f o r I r r a d i a t i o n s i n the S o l i d  State.  - 167  The  r e a c t o r c o n s i s t e d o f two  main p a r t s , A and  Part A consisted of a double-walled onto a f l a t - f a c e h a l f - d r u m . c i r c u l a t i o n of c o o l a n t h a l f - d r u m was  An  The  B ( F i g u r e 31  c y l i n d r i c a l brass  i n l e t and  through t h i s u n i t .  a gold-plated  i r r a d i a t e d were grown.  -  the f l a t  the  be was  j u n c t i o n of which An aluminum  foil  p o s i t i o n e d o v e r t h i s j u n c t i o n to s h i e l d i t from d i r e c t  radiation.  The  second j u n c t i o n o f the  j u n c t i o n and was  thermocouple served  k e p t i n an i c e - s l u r r y d u r i n g o p e r a t i o n s .  e s s e n t i a l l y a brass  c a s i n g f o r p a r t A and  a Pyrex window which a l l o w e d e x t e r n a l l y ; a groove w i t h  had  f o r the i r r a d i a t i o n o f the  reference  Part B  was  sample  an 0 - r i n g to make the system a i r - t i g h t a f t e r a vacuum t a k e o f f to an  f o r the e v a c u a t i o n  The  o f the r e a c t o r .  o f an U l t r a Kryomat K-80  as a  the f o l l o w i n g p r o v i s i o n s :  the i n s e r t i o n of p a r t A i n t o B; and  the  the  surface of  temperature a t the r e a c t i o n s i t e  s o l d e r e d onto the edge o f the g o l d e n groove.  r o o f was  for  c i r c u l a r groove where c r y s t a l s to  measured by a c o p p e r - c o n s t a n t a n thermocouple one was  drum s o l d e r e d  o u t l e t provided At  above).  DW  oil-pump  r e s t o f the a p p a r a t u s c o n s i s t e d  f o r the c o o l i n g and  c i r c u l a t i o n of coolant  through  r e a c t o r , a d i g i t a l - m i c r o v o l t m e t e r ( D M V ) the r e a d i n g o f w h i c h i s  94 c o n v e r t i b l e to  C using a copper-constantan c a l i b r a t i o n t a b l e  air-cooled glass f i l t e r f o r X >_ 355  nm)  (Corning  7380 f o r X >_ 340  nm  , an  or C o r n i n g  p o s i t i o n e d between the P y r e x window and  3850  the lamp  and  f i n a l l y a w a t e r - c o o l e d 450-Watt Hanovia lamp connected to a power In a t y p i c a l r u n , were weighed and zation.  Using  c r y s t a l s o f the compound to be  d i s s o l v e d i n 3-5  a disposable  ml o f the s o l v e n t ( s ) o f  p i p e t t e , the  s o l u t i o n was  source.  studied crystalli-  slowly  dropped  - 168  -  on t h e g r o o v e and a l l o w e d t o s l o w l y e v a p o r a t e and overnight.  crystallize  A c o v e r i n g o f aluminum f o i l p r o t e c t e d t h e sample from j  l i g h t and d u s t p a r t i c l e s d u r i n g t h i s s t a g e . The Kryomat was s e t a t t h e t e m p e r a t u r e chosen f o r a reaction.  The c o o l a n t was 50% (V/V) aqueous e t h y l e n e g l y c o l f o r  t e m p e r a t u r e s down t o -28°and CHCl-j f o r l o w e r t e m p e r a t u r e s . the of  While  c o o l a n t was b e i n g c o o l e d t o the d e s i r e d t e m p e r a t u r e , t h e f l o o r t h e r e a c t o r was  l i n e d w i t h f i l t e r paper.  This served to catch  any s o l i d s w h i c h might f l a k e o f f from the g r o o v e d u r i n g the r e a c t i o n . P a r t A was screws.  t h e n i n s e r t e d i n t o B and t h e two were s e c u r e d t o g e t h e r by  The i n l e t and o u t l e t l e a d s o f p a r t A were s e c u r e d t o the  a p p r o p r i a t e l e a d s o f the Kryomat.  The r e f e r e n c e j u n c t i o n o f t h e  t h e r m o c o u p l e was i n s e r t e d i n t o a dewar o f i c e - s l u r r y and t h e two t e r m i n a l s c o n n e c t e d t o the DMV.  The r e a c t o r was  t h e n e v a c u a t e d and  h e l d under vacuum f o r a minimum o f 15 m i n u t e s b e f o r e t h e c i r c u l a t i o n of  t h e c o o l a n t t h r o u g h the r e a c t o r was.begun.  A f t e r t h e DMV r e a d i n g  i n d i c a t e d t h e d e s i r e d t e m p e r a t u r e , a f u r t h e r 15 m i n u t e s were a l l o w e d for  the s y s t e m t o e q u i l i b r a t e and s t a b i l i z e .  and lamp were a l i g n e d  w i t h t h e P y r e x window.  M e a n w h i l e , the f i l t e r The lamp was  p o s i t i o n e d about 5" from t h e P y r e x window w h i c h , i n t u r n , was 4" from t h e sample.  Water c i r c u l a t i o n t h r o u g h t h e lamp j a c k e t  begun a t t h i s t i m e .  A s t e a d y j e t o f a i r was  glass f i l t e r  about was  d i r e c t e d onto the  t o p r e v e n t i t from o v e r h e a t i n g and c r a c k i n g .  A reflector  was p l a c e d b e h i n d the lamp t o m i n i m i z e d i s s i p a t i o n o f t h e l i g h t t o  - 169 -  the environment, and the lamp was switched on.  The DMV reading, the  pressure reading of the McLeod gauge attached to the vacuum l i n e , and the time of switching on the lamp were recorded.  For reactions  l a s t i n g 2 hours or l e s s , the reaction temperature was recorded at 10-15 minute i n t e r v a l s . .  Temperatures of reactions l a s t i n g longer  than 2 hours were recorded at longer time i n t e r v a l s .  The e n t i r e  temperature range of any run i s indicated i n the appropriate of the Experimental Section.  section  The vacuum attained i s .also given.  The longest continuous run was 13.00 hours.  Irradiations  lasting  longer than t h i s were c a r r i e d out discontinuously over a period not exceeding 3 days. At the end of a run, the cooling was stopped and the system allowed to reach room temperature before the vacuum was released  to prevent condensation of moisture on the reaction mixture.  Part A was taken out and l a i d h o r i z o n t a l l y .  Using disposable  pipettes and e i t h e r acetone or CHCl^, the sample was washed off groove.  the  The solvent was removed and the sample dried i n vacuo.  The % recovery of material from the reactor i s indicated for each run i n the appropriate section of the Experimental. Apparatus and Procedure for Irradiations  i n Benzene  Photolyses c a r r i e d out i n benzene at room temperature were done using a conventional external i r r a d i a t i o n apparatus.  Interposed  between the water-cooled 450-Watt Hanovia lamp and the solution was an  -  1 7 0  -  air-cooled Corning glass f i l t e r which was either No. 7380 transmitting X > 340 nm or No. 3850 transmitting X > 355 nm.  A l l solutions were  thoroughly deoxygenated f o r about 0.5 hour p r i o r to i r r a d i a t i o n and photolysed under Argon of <5 ppm oxygen content a v a i l a b l e from Canadian L i q u i d A i r . Apparatus and Procedure f o r Low Temperature I r r a d i a t i o n s i n Solution  Figure 32.  Apparatus f o r Low Temperature Irradiations i n Solution.  - 171 -  The apparatus consisted of a double-walled Pyrex vessel with an i n l e t and o u t l e t from the outer w a l l to allow f o r c i r c u l a t i o n of coolant. . The apparatus also had an outlet with a Teflon stopcock from i t s innerwall f o r easy sampling of the reaction mixture at i n t e r v a l s during the course of a reaction. were deoxygenated  Solutions  and photolysed under L grade high purity nitrogen  which was f i r s t passed through a tower of D r i e r i t e .  Gas i n l e t and  e x i t into the s o l u t i o n were through hypodermic needles inserted through an otherwise a i r t i g h t capplug stopper equipped with an alcohol thermometer precalibrated against a copper-constantan thermocouple. • Solutions were magnetically s t i r r e d .  Moisture condensation and i t s  subsequent freezing on the apparatus were mimimized by d i r e c t i n g a fast current of a i r over the sides of the reactor. were discontinuous but were completed within two days.  Irradiations As i n the  case of a l l other modes of i r r a d i a t i o n , the l i g h t source was a 450-Watt Hanovia lamp, and an air-cooled f i l t e r for  (Corning No. 7380  X >_ 340 nm and No. 3850 f o r X >^ 355 nm) was placed i n between  lamp and reactor.  Wavelength of I r r a d i a t i o n s Compounds 1^ through 8^ and substrate 10_ were studied at X >_ 340 nm. are  Compounds 9_ and 11^ were i r r a d i a t e d at A > 355 nm.  These  the same wavelengths at which these compounds have been studied  i n ' s o l u t i o n i n e a r l i e r work^.  - 172 -  Preparation of quinone  95  5a,8a-Dimethyl-4aB,5,8,8ag-tetrahydro-l,4-naphtho-  . , 1,  A s l u r r y o f 3.04 5.29  g (0.028 mole) o f p-benzoquinone  in  g o f t r a n s , t r a n s - 2 , 4 - h e x a d i e n e was h e a t e d under r e f l u x a t  w i t h s t i r r i n g u n t i l a l l o f the q u i n o n e had d i s s o l v e d . c o n t i n u e d f o r a f u r t h e r 15 m i n u t e s .  The m i x t u r e was  s t i r r i n g a t room t e m p e r a t u r e f o r 3 h o u r s . d i e n e i n vacuo l e f t 5.03  62°  H e a t i n g was then l e f t  Removal o f t h e e x c e s s  g (94%) o f a b r i g h t y e l l o w s o l i d .  C r y s t a l l i z a t i o n t w i c e from e t h e r - p e t r o l e u m e t h e r gave y e l l o w r o d s -of  1.  Mp  55-56° ( l i t .  Ir-.  (KBr),  NMR  5.92,  ( C C 1 ) 6, 6.62 4  v i n y l ) , 3.25  9 5  58-59.5°). 5.98  (C=0), 6.24  ( c o n j . C=C)  (S, 2H, C2 and C3 v i n y l ) , 5.53  (m, 2H, 4ag and 8ag m e t h i n e s ) , 2.50  m e t h i n e s ) , 1.12  y. ( s , 2H, C6 and (m, 2H, C5 and  C7 C8  ( d , J=7 Hz, 6H, m e t h y l s ) .  I r r a d i a t i o n o f Adduct 1_ i n KBr  I r r a d i a t i o n o f a 0.5% KBr p e l l e t o f 1^ f o r 1.5 hours l e d t o c o m p l e t e d i s a p p e a r a n c e o f t h e 6.24y a b s o r p t i o n o f 1_. i n a d d i t i o n , showed new C=0 a b s o r p t i o n s a t 5.82  The  and 5.90  infrared p.  I r r a d i a t i o n o f 1 i n the S o l i d S t a t e  A s o l u t i o n o f 114.9 mg o f 1^ i n p e t r o l e u m e t h e r was e v a p o r a t e d on t h e r e a c t o r ' s  groove and l e f t o v e r n i g h t .  The  slowly  -  -  173  r e s u l t i n g c r y s t a l s were i r r a d i a t e d a t 0.03 -1.5°  f o r 1 hour.  The r e c o v e r y was  98%.  t o r r between -2.0°  and  The r e s u l t i n g s o l i d  was  washed t h r i c e w i t h p e t r o l e u m e t h e r and t h e w a s h i n g s s t r i p p e d o f s o l v e n t and d r i e d i n vacuo t o g i v e 43.2 mg o f s o l i d w h i c h was by TLC, NMR  and i r t o be r e s i d u a l s t a r t i n g m a t e r i a l !L.  p r o d u c t was d r i e d i n vacuo.  T h i s gave 67.9 mg  The  shown  insoluble  (95% y i e l d ) o f IA.  The e x t e n t . o f r e a c t i o n c a l c u l a t e d from w e i g h t o f u n r e c o v e r e d 1_ was 62%.  Y i e l d s of IA a t other conversions are tabulated i n the t e x t .  An i n f r a r e d s p e c t r u m o f t h e crude p r o d u c t was t a k e n .  Following  this,  t h e crude m a t e r i a l was c r y s t a l l i z e d f r o m CHCl^-hexane t o g i v e s p a r k l i n g c o l o r l e s s p l a t e s s u i t a b l e f o r s i n g l e c r y s t a l X-ray s t r u c t u r e determination. Mp** Ir NMR  265.0° w i t h d e c o m p o s i t i o n . (KBr) ,  5.82  (CDC1 ) 6, 5.83  y.  (C=0)  ( s , 4H, v i n y l s ) , 3.47  3  m e t h i n e s ) , 3.22 2.50  and 5.90  ( s , 4H, c y c l o b u t a n e r i n g  (dd, J=3 and 2 Hz, 4H, C4, C9, C14 and C19 m e t h i n e s ) ,  (m, 4H, C5, C8, C15 and C18 m e t h i n e s ) , 1.10  ( d , J=7 Hz,  12H,  methyls). Mass s p e c t r u m m/e  p a r e n t 380  Anal. Calcd. f o r 4 2 8 ° 4 C  H  :  2  Found :  C  '  7  5  >  7  6  ;  H  »  7  C, 75.48; H,  ' ' 4 2  7.42.  P r e p a r a t i o n Of 6 , 7 - D i m e t h y l - 4 a 8 , 5 , 8 , 8 a B - t e t r a h y d r o - l , 4 - n a p h t h o q u i n o n e , 2. 96  R e c r y s t a l l i z e d p-benzoquinone suspended  i n 4.65  (3.14 g, 0.03 mole) was  g o f 2 , 3 - d i m e t h y l - l , 3 - b u t a d i e n e and h e a t e d a t  65°  - 174  under r e f l u x f o r 2 h o u r s . 2.92  -  Removal o f e x c e s s d i e n e i n vacuo gave  g (93%) o f c r u d e 2_ w h i c h was  d i s s o l v e d i n e t h e r and  filtered.  Removal o f e t h e r f o l l o w e d by c r y s t a l l i z a t i o n once f r o m e t h a n o l t w i c e from petroleum Mp Ir NMR  e t h e r gave p a l e y e l l o w c r y s t a l s o f  115-116°. ( l i t . ( K B r ) , 5.93  ( c o n j . C=C)  y.  ( s , 2H, C2 and C3 v i n y l s ) , 3.10  3  2.20  2.  115-117°).  (C=0), 6.24  (CDC1 ) 6, 6.58  C8a m e t h i n e s ) ,  9 6  and  (m, 4H,  C5 and C8 m e t h y l e n e s ) ,  (m, 2H, C4a 1.63  and  ( s , 6H,  methyls).  - I r r a d i a t i o n o f Adduct 2_ i n KBr  A 0.5%  KBr p e l l e t o f 2 was  r e a c t i o n monitored  by i r .  a b s o r p t i o n o f 2_ was  irradiated  c o m p l e t e l y gone.  I r r a d i a t i o n o f 2_ i n t h e S o l i d  I n a d d i t i o n , the 5.93y  covered P y r e x p e t r i d i s h f o r 0.4  hour.  washed t h r e e t i m e s w i t h c h l o r o f o r m and  The  the w a s h i n g s  showed o n l y r e s i d u a l 2_.  recovered  mg.  The  crude y i e l d was  36.1  mg  absorption.  resulting solid  ( s i l i c a g e l ; chloroform).  The  C=0  were i r r a d i a t e d i n a  a base s p o t , the TLC 55.8  the  State  C r y s t a l s o f compound 2_ (93.0 mg)  2_ was  and  A f t e r 5 h o u r s o f i r r a d i a t i o n , the 6.24y  s t r e t c h o f 2_ had been r e p l a c e d by a 5.85y C=0  and a n a l y z e d by TLC  (X >_ 340 nm)  s o l i d product  (97%).  was  concentrated  With the e x c e p t i o n of The  2A was  dry weight of d r i e d i n vacuo.  The e x t e n t o f r e a c t i o n (%  conversion)  -  -  175  c a l c u l a t e d from unrecovered 2_ was  40%.  Y i e l d s o f 2A from o t h e r  runs a t v a r y i n g c o n v e r s i o n s a r e g i v e n i n the t e x t . s p e c t r u m o f the c r u d e p r o d u c t was r e c o r d e d .  The  infrared  Crystallization  from  c h l o r o f o r m a f f o r d e d t i n y , s p a r k l i n g , c o l o r l e s s p l a t e s o f 2A. Mp** Ir NMR  264.7° w i t h d e c o m p o s i t i o n . ( K B r ) , 5.85  (C=0) y.  (CDC1 ) 6, 3.64  .  ( s , 4H, c y c l o b u t a n e r i n g m e t h i n e s ) , 3.18  3  C4, C9, C14 and C19 m e t h i n e s ) , 2.22  (m, 8H, m e t h y l e n e s ) , 1.66  (m,  4H,  (s,  12H, m e t h y l s ) . Mass spectrum m/e  p a r e n t 380.  Anal. Calcd. f o r 4 2 8 ° 4 C  H  :  2  Found :  C, 75.76; H, C, 75.61; H,  7.42. 7.29.  N o t e s o f 2A C r y s t a l Used f o r X - r a y S t r u c t u r e D e t e r m i n a t i o n  The c r y s t a l s o b t a i n e d by c r y s t a l l i z i n g from c h l o r o f o r m were too s m a l l f o r use i n t h e X - r a y s t r u c t u r e d e t e r m i n a t i o n .  Larger s i n g l e  c r y s t a l s f o r t h i s p u r p o s e were o b t a i n e d by c r y s t a l l i z i n g crude 2A from a c e t o n i t r i l e .  The i r o f t h i s b a t c h o f 2A c r y s t a l s was  identical  i n e v e r y r e s p e c t t o t h e i r o f c r u d e 2A as w e l l as t o t h e 2A t h a t had been c r y s t a l l i z e d from c h l o r o f o r m . P r e p a r a t i o n o f 4aB,5,8,8ag-Tetrahydro-l,4-naphthoquinone , 55  2.  A s o l u t i o n p f 1,4-benzoquinone w h i c h had been c r y s t a l l i z e d t w i c e from a c e t o n e - p e t r o l e u m e t h e r was made by d i s s o l v i n g 13.0 g  - 176  -  (0.12 mole) i n 200 ml o f benzene i n a h y d r o g e n a t i o n b o t t l e . s o l u t i o n was  c o o l e d t o 0°, and 18 ml o f 1,3-butadiene  The  w h i c h had been  condensed t o l i q u i d u s i n g d r y - i c e a c e t o n e was  added and t h e  f i r m l y s t o p p e r e d and r e p l a c e d i n i t s s h i e l d .  The  stopper  bottle  was  s e c u r e d by screws i n a r o c k e r o f a h y d r o g e n a t i o n a p p a r a t u s and s o l u t i o n m e c h a n i c a l l y r o c k e d f o r 21 d a y s . s o l u t i o n was  The r e s u l t i n g y e l l o w  s t r i p p e d o f s o l v e n t and e x c e s s d i e n e l e a v i n g an o i l  w h i c h s o l i d i f i e d on c o o l i n g i n i c e .  I t was  c r y s t a l l i z e d once from  p e t r o l e u m e t h e r and t w i c e f r o m e t h e r - p e t r o l e u m e t h e r . t h e t h r e e c r y s t a l l i z a t i o n s was Mp  53.5-54° ( l i t .  Ir  ( K B r ) , 5.97  NMR  5 5  The y i e l d  after  61%.  52-54°).  (C=0), 6.24  ( C C l ^ ) 6, 6.57  v i n y l s ) , 3.15  the  ( c o n j . C=C)  y.  ( s , 2H, C2 and C3 v i n y l s ) , 5.63  (m, 2H, 4a,8a m e t h i n e s ) , 2.28  (m, 2H, C6 and  (m, 4H, C5 and  C7  C8  methylenes). I r r a d i a t i o n o f 3 i n KBr  A 0.7% 3 hours.  KBr p e l l e t o f 3 was  (A >_ 340 nm)  I r o f t h e i r r a d i a t e d p e l l e t showed complete  o f the c o n j u g a t e d C=C shifted  irradiated  from 5.97  s t r e t c h a t 6.24y.  t o 5.88  The C=0  for  disappearance  a b s o r p t i o n had  also  y.  I r r a d i a t i o n o f _3 i n the S o l i d S t a t e  C r y s t a l s o f compound _3 (135.5 mg) t o r r between 4.3°  and 0.0°  f o r 1 hour.  The  were i r r a d i a t e d a t  0.01  s o l i d was washed o f f t h e  - 177 -  reactor's cavity with acetone and chloroform. and drying i n vacuo l e f t 124.0 mg of s o l i d  Removal of solvents  (H92% recovery).  redissolved i n chloroform and suction f i l t e r e d .  It was  The f i l t r a t e  was  concentrated and checked by TLC ( s i l i c a g e l ; chloroform).  Apart  from a base spot, the only other spot was that of s t a r t i n g  material,  _3.  The chloroform soluble portion was 8.2 mg.  insoluble s o l i d was 117.6 mg (92% y i e l d ) .  The chloroform  Infrared spectra of the  crude s o l i d and also of the recovered s t a r t i n g material were recorded.  The l a t t e r was confirmed to be r e s i d u a l _3.  product was c r y s t a l l i z e d from refluxing chloroform. thus obtained were c o l o r l e s s ,  sparkling f l a k e s .  The The c r y s t a l s  The i r of the  c r y s t a l l i z e d material was i d e n t i c a l to that of the crude product, 3A. Yields of 3A from other runs.are given i n the text. Mp** Ir  2 8 0 ° ± 2 ° with decomposition. (KBr), 5.85  (C=0)  NMR (CDC13) 6, 5.70 methines), 2.30  Compound 3A had  3.20  y.  (m, 4, v i n y l s ) , 3.64  (s,  4H, cyclobutane r i n g  (m, 4H, C4, C9, C4 and C19 bridgehead  methines),  (m, 8H, methylenes).  Mass spectrum m/e parent Anal. Calcd. for  c 2  324.  oH20°4: Found :  C  '  7 4  *  0 6 ;  H  »  6  -  2 2  -  C, 73.88; H, 6.15.  Notes on 33. C r y s t a l Used for X-ray Structure Determination The c r y s t a l s of _3A obtained from c r y s t a l l i z i n g from chloroform  V  - 178  -  were too small and thin f o r single c r y s t a l X-ray determination.  structure  Larger c r y s t a l s f o r t h i s purpose were obtained by  c r y s t a l l i z i n g from a c e t o n i t r i l e .  The i n f r a r e d spectrum of t h i s mate-  r i a l (3B) i s discussed i n the text.  I t s NMR  was i d e n t i c a l to that of  3A c r y s t a l l i z e d from chloroform. I r r a d i a t i o n of Adduct 3. i n Benzene A solution of 406.0 mg of compound _3 i n 200 ml benzene was degassed and photolysed f o r 24.2 hours.  The r e s u l t i n g milky solution  was f i l t e r e d and the s o l i d component dried and weighed. was 165.0 mg.  I t s weight  Ir of the crude material showed a broad OH at 2.90u  and a C=0 absorption at 5.87u.  The absorptions were generally very  broad e s p e c i a l l y i n the f i n g e r p r i n t region. NMR  ((CD ) CO) 6, 6.80 3  2  adding D 0), 1.53 2  Mass spectrum:  ( s ) , 5.07  (br,m), 2.51  (br,s, broadens  on  (m).  highest observed m/e  = 495.  The f i l t r a t e was concentrated and separated by GLC (5' x V  of 20% DEGS on 60/80 Chromosorb W at 150° and 150 ml/min).  Two peaks with retention were obtained.  times of 4 and 6 minutes,  respectively  They were subsequently i d e n t i f i e d as 3_C and 3D by  comparing  t h e i r ir's with those of authentic samples.  retention  time = 6 minutes, was the major.  Of the two,  3D,  - 179  -  P r e p a r a t i o n o f 6,7-Dipheny.l-4aB,5,8,8aB^etrahydro-l,4-naphthoquinone * , 4. :  T h i s was  /  a four-step synthesis comprising  (a) The p r e p a r a t i o n o f b e n z i l d i h y d r a z o n e  97 a from b e n z i l - , 97 a  (b) the c o n v e r s i o n o f the b e n z i l d i h y d r a z o n e  to diphenylacetylene  ,  (c) the c o n v e r s i o n o f the d i p h e n y l a c e t y l e n e t o 2 , 3 - d i p h e n y l - l , 3 butadiene ^,  and  9  (d) the D i e l s - A l d e r r e a c t i o n between the d i e n e from p a r t (c) and 97 c p-benzoquinone t o g i v e k_  .  (a) A s o l u t i o n o f 105.1  g (0.5 mole) o f b e n z i l and 76.0  h y d r a z i n e h y d r a t e i n 325 ml o f n - p r o p y l a l c o h o l was hours.  The  r e s u l t i n g r e d s o l u t i o n was  refluxed for  85% 61.5  f i r s t c o o l e d t o room t e m p e r a t u r e  and then c o o l e d i n an i c e - b a t h f o r one hour. was  g of  The b e n z i l h y d r a z o n e  f i l t e r e d , washed w i t h a t o t a l o f 200 ml o f e t h a n o l i n p o r t i o n s and  then d r i e d i n vacuo f o r one hour. (b) The b e n z i l h y d r a z o n e was  T h i s gave 100.4  g of b e n z i l hydrazone.  t r a n s f e r r e d to a o n e - l i t r e three-  necked f l a s k f i t t e d w i t h a r e f l u x condenser and a m e c h a n i c a l and 480 ml o f benzene added.  Y e l l o w HgO  (240 g) was  added i n s m a l l  amounts t o the suspended m i x t u r e o v e r a p e r i o d o f 1.5 s t i r r i n g and  g e n t l e h e a t i n g o v e r a steam b a t h .  the m i x t u r e was  f u r t h e r s t i r r e d f o r 1.5  h o u r s d u r i n g w h i c h time  The m i x t u r e was  t e m p e r a t u r e o v e r n i g h t and t h e n f i l t e r e d .  hours w i t h  A f t e r the a d d i t i o n ,  v i g o r o u s r e a c t i o n accompanied by f r o t h i n g o c c u r r e d . c o n t r o l by c o o l i n g i n an i c e b a t h .  stirrer  I t was  a  k e p t under  l e f t a t room  The r e s i d u e was  100 ml o f benzene and the w a s h i n g s added t o the f i l t r a t e .  washed w i t h The  latter  -  180  -  was  d r i e d o v e r anhydrous Na2S0^, f i l t e r e d and  The  r e s i d u e was  d i s t i l l e d a t 0.02  of p a l e y e l l o w s o l i d  t o r r and  s t r i p p e d of s o l v e n t .  125°.  T h i s gave 62.1  diphenylacetylene.  C r y s t a l l i z a t i o n f r o m 95% e t h a n o l gave 53.7 a c e t y l e n e , m.p.  g  56-58° ( l i t .  9  7  (c) A 500 ml t h r e e - n e c k e d  g of d i p h e n y l -  60-61°).  a  round-bottomed f l a s k was  fitted  with  a s e a l e d m e c h a n i c a l s t i r r e r , a r e f l u x c o n d e n s e r and a thermometer. A T - j o i n t was two  attached  t o the top o f the c o n d e n s e r .  remaining  arms o f the T - j o i n t were c o n n e c t e d t o a s o u r c e o f pure n i t r o g e n  and a b u b b l e r  respectively.  The  f l a s k was  and 5 g o f d r y sodium h y d r i d e and  under N  2  The m i x t u r e was  w i t h s t i r r i n g f o r 40 m i n u t e s .  using a water-bath.  f u n n e l c o n t a i n i n g 17.8  The  The  heated t o  r e p l a c e d by a  This l a t t e r  f u n n e l was  h e a t e d to and m a i n t a i n e d  c o o l e d t o room t e m p e r a t u r e and  f o r 2.5  ml  added  F o l l o w i n g the a d d i t i o n ,  hours.  I t was  the r e d d i s h - b r o w n m i x t u r e  poured o v e r i c e w i t h s t i r r i n g and The  s o l u t i o n was  mixture  subsequently slowly  l e f t a t room t e m p e r a t u r e u n t i l a l l  c r u d e m i x t u r e was  e x t r a c t e d f i v e times  with  200 ml p o r t i o n s o f e t h e r and the combined e t h e r e a l e x t r a c t s washed w i t h 300 ml o f w a t e r and  to  dropping  i n 80  r e p l a c e d by the thermometer and the a t 70°  75°  then cooled  g (0.1 mole) o f d i p h e n y l a c e t y l e n e  d r o p w i s e t o the g r e y c o n t e n t s o f t h e f l a s k .  t h e i c e had m e l t e d .  f l a s k was  thermometer was  o f anhydrous d i m e t h y l s u l f o x i d e .  the dropping  flushed with nitrogen  120 ml o f anhydrous d i m e t h y l  s u l f o x i d e i n t r o d u c e d i n t o the f l a s k .  30°  The  t h e n d r i e d o v e r anhydrous sodium s u l f a t e .  - 181' -  Removal of the ether i n vacuo l e f t 16.4 g of a reddish-brown o i l which was divided into two p o r t i o n s .  Each p o r t i o n was chromatographed  on 200 g columns of neutral alumina using as eluents benzene-hexane, (1:7) and then (1:3).  The pale yellow f r a c t i o n s were combined and  stripped of solvents i n vacuo to give 12.0 g of impure 2,3-diphenyl1,3-butadiene  as an o i l .  It was used i n the procedure described below  without further p u r i f i c a t i o n . (d) A l l of the o i l from part  (c) and 3.0 g (0.03 mole) of p-  benzoquinone were dissolved i n 80 ml of benzene and refluxed for 18 hours. The mixture was cooled  to room temperature and stripped of solvent.  Hexane was added i n small portions u n t i l p r e c i p i t a t i o n had ceased. The p r e c i p i t a t e was f i l t e r e d and washed twice with cold hexane.  It  was d r i e d i n a i r to give 3.9 g of compound 4 as a greenish-yellow s o l i d (45% y i e l d based on p-benzoquinone). acetone-hexane  to give pale yellow needles.  Mp  163-164.5°  Ir  (KBr), 5.92 and 5.95  (lit.  NMR (CDC13) 6, 7.10 3.47  It was c r y s t a l l i z e d twice from  9 7  (s,  °  163°). (C=0), 6.24  (conj. C=C) y.  10H, aromatic), 6.68 (s,  (m, 2H, C4a and C8a methines), 2.77  2H, C2 and C3 v i n y l s ) ,  (m, 4H, C5 + C8 methylenes).  I r r a d i a t i o n of 4 i n KBr The i r r a d i a t i o n , X >_ 340 nm, of a 0.4% KBr p e l l e t of 4_ for twenty minutes led to i t s complete depletion as shown by the  disappearance  of a moderately intense peak (^46% of the absorbance of the C=0 peak) at  11.52y.  - 182 -  I n t h e c a r b o n y l r e g i o n , the,5.92 and 5.95 y due t o 4^ had been r e p l a c e d by a s i n g l e C=0 In a d d i t i o n , a b r o a d but d i s t i n c t The i r r e c o r d e d a new p r o d u c t 0.5 h o u r .  formation  noted.  after further irradiation indicated  a f t e r a t o t a l i r r a d i a t i o n time o f  T h i s new p r o d u c t  till  a b s o r p t i o n a t 5.97y.  OH a b s o r p t i o n a t 2.91y was  had a 5.72y C=0.  i n t e n s i t y a t the expense o f the 5.97y C=0 product  absorptions  It increased i n  absorption  of the p r i m a r y  i t e v e n t u a l l y became the most i n t e n s e o f the two  c a r b o n y l peaks a f t e r 6 h o u r s .  I r r a d i a t i o n of A i n t h e S o l i d  State  C r y s t a l s o f compound 4^ (50.0 mg) 0.05 was  were i r r a d i a t e d a t  t o r r between -10.4° and -9.8° f o r 15 m i n u t e s . recovered.  94% of m a t e r i a l  P r e p a r a t i v e TLC ( s i l i c a g e l ; 15% e t h y l a c e t a t e - ,  benzene) o f t h e m i x t u r e gave 41.3 mg o f r e s i d u a l 4^ and 5.8 mg o f the p r o d u c t  4A.  m a t e r i a l , was  The e x t e n t  o f r e a c t i o n , b a s e d on r e c o v e r e d  17% and t h e y i e l d of p r o d u c t  In a n o t h e r r u n , ,136.7 mg  gave 46.4 mg  67%.  of h_ was  t o r r between 18.5° and 22.0° f o r 2 h o u r s .  starting  i r r a d i a t e d at  0.02  P r e p a r a t i v e TLC as b e f o r e  o f r e s i d u a l 4^ 7.1 mg o f 4B_ and 41.2 mg  of 4A.  The  y i e l d s o f 4B and 4A were, t h u s , 8% and 47% r e s p e c t i v e l y . L a s t l y , i r r a d i a t i o n of 83.0 mg  o f 4_ a t 0.01  torr  between  17.3° and 18.5° f o r 11 h o u r s f o l l o w e d by p r e p a r a t i v e TLC gave 6.2 of r e s i d u a l 4^, 11.7 mg  o f 4B and 25.7 mg  o f 4A.  The y i e l d s of  mg  these  - 183 -  two p r o d u c t s were, t h e r e f o r e , 15% and 33% r e s p e c t i v e l y . The p r o d u c t s 4A and 4B were c r y s t a l l i z e d  ]  from acetone-  hexane; 4A was w h i t e , f e a t h e r y n e e d l e s . Mp  189.5°-190.0°.  Ir  ( K B r ) , 2.92 (OH), 5.97 (C=0) y.  NMR  (CDC1 ) 6, 7.17 (m, 10H, p h e n y l s ) , 6.44 ( d , J=10 Hz, I H , C2 3  v i n y l ) , 6.30 ( d , J=3 Hz, I H , C9 v i n y l ) , 6.01 ( d d , J=10 and 2 Hz, I H , C3 v i n y l ) , 3.45 ( d , J=3 Hz, I H , CIO m e t h i n e ) , 2.73 ( s , I H , d i s a p p e a r s on a d d i n g I^O, OH), 2.65 (m, 2H, C6 m e t h y l e n e s ) , 2.13 (dd, J=14 and 9 Hz, I H , C5 m e t h i n e ) . Mass spectrum m/e p a r e n t 314. A n a l . C a l c d . f o r C__H 0_:  C, 84.05; H, 5.77.  Found :  C, 84.06; H, 5.87.  1o  P r o d u c t 4B c r y s t a l l i z e d Mp  170.5°-171.5°  Ir  ( K B r ) , 5.73 (C=0)  NMR  as c o l o r l e s s n e e d l e s .  6.25 ( c o n j . C=C) y.  (CDC1 ) 6, 7.23-6.87 (m, 10H, a r o m a t i c ) , 3.23 (m, 2H, C7 and 3  CIO m e t h i n e s ) , 3.07 (m, 1H-, C5 m e t h i n e ) , 2.83 (m, 3H, C l m e t h i n e and 69 C4 m e t h y l e n e s ) , calcd.  6 9  calcd.  2.49 ( d d , J=20 and 5 Hz, I H , C8 e x o ) ,  2.30 ( d d , J=20 and 1.5 Hz, C8 endo).  Mass spectrum m/e p a r e n t 314. A n a l . C a l c d . f o r C-.H._0 : o  2.2.  l o  C, 84.05; H, 5.77.  2.  Found :  C, 83.95; H, 5.71.  -  184  -  B a s e - C a t a l y z e d D e u t e r i u m Exchange o f Ene-Dlone 4B S i x d r o p s o f a 2N s o l u t i o n , of KOH i n T)^0 were added t o the NMR  sample o f 4B.  The tube was p e r i o d i c a l l y shaken.  r e c o r d e d a f t e r 12 h o u r s showed no changes.  A spectrum  However, a f t e r 4.5 d a y s ,  the 2.496 r e s o n a n c e s a t t r i b u t e d t o t h e C8 exo p r o t o n had d i s a p p e a r e d , the d o u b l e t o f d o u b l e t r e s o n a n c e s due t o . t h e C8-endo p r o t o n - h a d c o l l a p s e d t o a b r o a d s i n g l e t a t 2.316 and t h e s m a l l s p l i t t i n g o f t h e multiplet  a t 3.236 was no l o n g e r p r e s e n t .  The r e m a i n d e r o f t h e  s p e c t r u m remained unchanged.  P h o t o l y s i s o f 4. i n Benzene A s o l u t i o n o f 214.9 mg o f compound 4_ i n 100 m l o f benzene was degassed and i r r a d i a t e d , f o r 3.0 h o u r s .  The s o l v e n t was  removed i n vacuo and t h e r e s u l t i n g m i x t u r e s e p a r a t e d by p r e p a r a t i v e TLC ( s i l i c a g e l ; 15% e t h y l a c e t a t e - b e n z e n e ) .  T h i s gave 31.0 mg  of 4B and 85.2 mg o f 4A.(Combined y i e l d s = 54%.  R a t i o o f 4A:4JL = 3 : 1 . )  I n a n o t h e r r u n , 100.0 mg o f 4_ i n 100 m l o f benzene was degassed and p h o t b l y s e d f o r 3.1 h o u r s .  Treatment o f t h i s m i x t u r e  as above gave 8.2 mg o f r e s i d u a l 4_, 24.8 mg of 4B_ and.34.1 mg o f 4A. (Combined y i e l d o f p r o d u c t s = 64%.  R a t i o o f 4A:4B = 3:2.)  Finally,  p h o t o l y s i s o f a s o l u t i o n of 159.7 mg o f 4_ i n 100 m l o f benzene f o r 3.9 h o u r s f o l l o w e d by p r e p a r a t i v e TLC gave 57.1 mg o f ^B_ and 26.3 mg of 4A.  (Combined y i e l d s = 52%.  R a t i o o f 4A:4B =  1:2.)  - 185  -  The m.p.'s and s p e c t r a o f p r o d u c t s 4A and 4B were i d e n t i c a l t o t h o s e r e p o r t e d f o r the s o l i d s t a t e p h o t o l y s i s p r o d u c t s . A n a l y t i c a l Run:-  A s o l u t i o n of 23.0 mg o f adduct 4, i n 10.ml  benzene was degassed and i r r a d i a t e d .  A l i q u o t s were w i t h d r a w n a t  0.1 hour i n t e r v a l s , and used f o r a n a l y s e s by TLC e t h y l a c e t a t e - b e n z e n e ) and i r . A f t e r  of  ( s i l i c a g e l ; 15%  0.1 h o u r o f i r r a d i a t i o n , a  peak a t 8.42u c h a r a c t e r i s t i c o f e n o n e - a l c o h o l p r o d u c t , 4A, had begun to develop i n the i r . TLC.  The p r e s e n c e o f 4A was  A l s o i n t h i s i r , a b r o a d e n i n g was  further  c o n f i r m e d by  o b s e r v e d i n t h e 5.70y  r e g i o n i n d i c a t i n g t h e p r e s e n c e o f t h e e n e - d i o n e , 4B.  In the i r  of t h e sample w i t h d r a w n a f t e r 0.2 hour o f i r r a d i a t i o n , t h e 2.97u OH s t r e t c h a t t r i b u t a b l e  t o 4A became a p p a r e n t .  s p e c t r a o f samples w i t h d r a w n a f t e r 0.3, 0.4 tion respectively,  and 0.5 hour o f i r r a d i a -  the s t a r t i n g m a t e r i a l ,  In  depleted.  shown by t h e p e r s i s t e n c e o f t h e m o d e r a t e l y i n t e n s e peak  a t 11.52u due t o 4/ peak.)  subsequent  peaks due t o 4A and 4B s t e a d i l y i n c r e a s e d .  none o f t h e f i v e s a m p l i n g s was T h i s was  In  T h i s was  ( I t s i n t e n s i t y - 46% t h e absorbance of the  c o n f i r m e d by  I r r a d i a t i o n o f P h o t o p r o d u c t AA Crystals  TLC.  i n the S o l i d State  of t h e e n o n e - a l c o h o l p h o t o p r o d u c t , 4A (17.0  were p h o t o l y s e d a t 0.05  C=0  t o r r between 17.5°  I r of t h e r e s i d u e showed a 5.73y C=0  and 18.2°  mg)  f o r 12 h o u r s .  c h a r a c t e r i s t i c o f t h e ene-dione  4B.  _ 186 _  P h o t o l y s i s of P h o t o p r o d u c t 4A 'in Benzene  A solution  of 24.4 mg o f p h o t o p r o d u c t 4A i n 20 m l of  benzene was degassed and p h o t o l y s e d . by TLC  The r e a c t i o n  ( s i l i c a g e l ; 15% e t h y l a c e t a t e - b e n z e n e ) .  After  i r r a d i a t i o n , two s p o t s were d e t e c t e d i n a d d i t i o n The r e a c t i o n  was  The m i x t u r e was  s p o t had 5.68 structure  4C.  monitored 0.6 hour o f  t o t h a t of 4A.  s t o p p e d a f t e r 2.1 hours o f t o t a l i r r a d i a t i o n .  of t h e c r u d e m i x t u r e showed b r o a d C=0 5.90 u.  was  and 5.80  s t r e t c h e s a t 5.65, 5.75  s e p a r a t e d by p r e p a r a t i v e TLC.  u C=0  Ir and  The uppermost  s t r e t c h e s i n t h e i r and was a s s i g n e d  The m i d d l e s p o t had a 5.73u C=0  characteristic  4B, and t h e l o w e r s p o t had a 2.92u OH and a 5.90u C=0 c o n s e q u e n t l y i d e n t i f i e d as r e s i d u a l  and  of  was  4A.  I r r a d i a t i o n o f P h o t o p r o d u c t 4B i n KBr The i r r a d i a t i o n of a 0.4% KBr p e l l e t o f 4JS was  followed  by i r a t h o u r l y i n t e r v a l s up t o 11.1 hours o f t o t a l i r r a d i a t i o n . There was no change  i n the i r .  I r r a d i a t i o n o f P h o t o p r o d u c t AB_ i n Benzene A solution  o f 10.0 mg o f ene-dione 4B_ i n 10 m l of benzene  was degassed and i r r a d i a t e d sample was  f o r 2 hours.  i d e n t i c a l t o t h a t of 4B.  The i r o f t h e i r r a d i a t e d  - 187  Preparation of  "  2,3,6,7-Tetramethyl-4aB,5,8,8aB-tetrahydro-l,498  naphthoquinone (a)  , 5_  2,3-Dimethyl-l,4-benzoquinone. 98a The procedure i s that described by Pieser  preparation of quinones.  f o r the  A t w o - l i t e r f l a s k having a long neck  was set up f o r steam d i s t i l l a t i o n .  The condenser from t h i s f l a s k  was connected by means of an adapter to a t w o - l i t e r , round-bottomed, short-necked  f l a s k which served as the r e c e i v e r .  This l a t t e r  was submerged i n a bucket of i c e s l u r r y and was equipped with a second condenser clamped i n a v e r t i c a l p o s i t i o n .  These measures  were taken to prevent loss of the v o l a t i l e quinone.  Water was  started running through both condensers and the reaction f l a s k disconnected.  Dry, w e l l powdered 3-amino-o-xylene s u l f a t e (12.63 g)  was introduced i n t o the reaction f l a s k .  Concentrated ^SO^  (45 ml)  was d i l u t e d with 200 ml of 1^0, cooled, and added to the contents of the f l a s k .  Powdered Mn0  2  (20.44 g) was added next and the  f l a s k quickly swirled to mix the contents and then immediately connected to the rest of the apparatus. distilled.  The contents were steam  Occasionally, the condenser between the reaction f l a s k  and the receiver became clogged with the quinone and i t became necessary to temporarily stop the water running through t h i s condenser to allow the quinone to d i s t i l l into the receiver. 1 hour, the d i s t i l l a t i o n was ended.  After  A small amount of the quinone  lodged i n the condenser was washed into the receiver with ether.  - 188 -  An additional 100 ml of ether was  added to the quinone and the  resulting ethereal s o l u t i o n d r i e d over anhydrous Na^SO^ for a few hours.  The ether was removed i n vacuo and the o-xyloquinone  so  produced used i n the next step without further p u r i f i c a t i o n .  (b)  2,3,6,7-Tetramethyl-4ag,5,8,8af3-tetrahydro-l,4-naphthoquinone  98b - , 5.  A l l of the quinone prepared above was dissolved i n 10 ml of ethanol i n a 50 ml round-bottomed f l a s k .  Three ml of 2,3-  dimethyl-l,3-butadiene was added and the mixture refluxed f o r 8.5 hours.  It was subsequently stripped of solvent i n vacuo and the  resulting s o l i d c r y s t a l l i z e d from petroleum ether using Norit to decolorize.  A further r e c r y s t a l l i z a t i o n gave crystals of _5.  Mp  104.0-104.5° ( l i t .  Ir  (KBr), 5.95  NMR  9 8 b  and 5.98  (CCl^) 6, 3.07  105-106.5°). (C=0), 6.18  (conj. C=C)  y.  (m, 2H, C4a and C8a methines), 2.13  and C8 methylenes), 1.97  (m, 4H, C5  (s, 6H, C2 and C3 methyls), 1.63  (s, 6H,  C6 and C7 methyls).  I r r a d i a t i o n of 5_ i n KBr  A 0.7% KBr p e l l e t of 5_ was for a t o t a l of 12 hours. new  peaks.  i r r a d i a t e d discontinuously  I r recorded at hourly i n t e r v a l s showed no  - 189 -  I r r a d i a t i o n of 5_ i n the S o l i d State  Crystals of compound 5_ (35.8 mg) were i r r a d i a t e d at 0.03  t o r r between 8.0° and 9.3° f o r a t o t a l of 30.3 hours.  recovery was 86%.  TLC ( s i l i c a g e l ; 15% e t h y l acetate-benzene) showed  a s i n g l e spot with an Rf i d e n t i c a l to that of 5_. of  The  The i r and  NMR  the i r r a d i a t e d sample were also i d e n t i c a l to those of 5_. 99  Preparation of 2 3-Dimethyl-l,4 4aS 9aB-tetrahydro-9 10-anthraquinone >  >  >  >  , 6,  A s o l u t i o n of 8.0 g (0.05 mole) of 1,4-naphthoquinone and 8.0 g (0.1 mole) of 2,3-dimethyl-l,3-butadiene i n 100 ml of ethyl alcohol was refluxed f o r 5 hours. the mixture s o l i d i f i e d .  On cooling to room temperature,  It was l e f t i n the r e f r i g e r a t o r overnight.  The s o l i d was broken up with a spatula and sucked dry.  It was  washed three times with 15 ml portions of cold ethanol and dried i n vacuo f o r 3 hours.  The y i e l d was 10.9 g (91%).  I t was  from acetone with Norit to remove colored impurities. 7.7 g of sparkling c o l o r l e s s c r y s t a l s .  crystallized  This gave  During a subsequent  r e c r y s t a l l i z a t i o n from acetone, two d i s t i n c t c r y s t a l s were formed, one (the major) was c o l o r l e s s rods of the desired adduct, j6; the other was bright yellow plates which darkened on exposure to a i r for prolonged periods. suggested i t might be  The i r and NMR  2,3-dimethyl-l,4-dihydro-9,10-anthraquinone  formed by p a r t i a l a i r oxidation of j6. 148.5° ( l i t .  of t h i s l a t t e r compound  150.0°).  Adduct 6_ had mp  . 148.0-  - 190 -  Ir NMR  (KBr), 5.92  (C=0), 6.26  (conj. C=C)  y.  (CDC1 ) 6, 8.23-7.56 (m, AH, phenyl), 3.38 3  methines), 2.31  (m, 2H, C4a and  (m, 4H, C l and C4 methylenes), 1.68  C9a  (s, 6H, methyls).  I r r a d i a t i o n of & i n KBr A 0.4% KBr p e l l e t of 6^ was the reaction monitored by i r .  i r r a d i a t e d (X >_ 340 nm)  and  The i r taken a f t e r 26.4 hours of  i r r a d i a t i o n showed an OH peak at 2.90u.  The C=0 absorption of §_  at 5.92u was unchanged but the i n t e n s i t y of the conjugated  C=C  absorption at 6.26u was reduced r e l a t i v e to the C=0 absorption.  I r r a d i a t i o n of 6_ i n the Solid State Crystals of compound b_ (132.4 mg) were i r r a d i a t e d i n vacuo (0.02 torr) between 8.3° and 10.0° f o r a t o t a l of 30.8 A pale yellow s o l i d (131.9 mg = 100% recovery) was TLC  hours.  obtained. Preparative  ( s i l i c a g e l ; 15% ethyl acetate-benzene) "of.the reaction  mixture  gave 58.3 mg of r e s i d u a l 6^ and 44.6 mg of product 6A (60% y i e l d ) . Small amounts (^5% each) of the quirioi and the dihydro analog of 6_ were also i s o l a t e d .  The product, 6A, was washed with hexane, dried  and sublimed at 103° and 0.03  torr.  Subsequent c r y s t a l l i z a t i o n from  acetone-benzene gave colorless c r y s t a l s of 6A.  2Aa Mp Ir NMR  ^24.5-125.5°, ( l i t . (KBr), 2.90  (OH), 5.93  126;0-126.5°). (C=0), 6.23  (conj. C=C)  (CDC1,) 6, 8.00-7.25 (m, 4H, aromatic), 5.74  y. .  (m, IH, C9 v i n y l ) ,  - 191 -  3.22  (d, J=3 Hz, IH, CIO methine), 2.79  adding D 0, 2  (d, J=1.5 1.34  OH), 2.54  (s, IH, disappears on  (dd, J=8 and 3 Hz, IH, C5 methine),  Hz, 3H, C8 methyl), 1.58  (dd, J=13 and 3 Hz, IH, C6 endo),  (dd, J=13 and 3 Hz, IH, C6 exo), 1.01  Mass spectrum m/e  1.83  (s, 3H, C7 methyl).  parent 240.  I r r a d i a t i o n of jj i n the S o l i d State.  C a l c u l a t i o n of Extent of Reaction  C r y s t a l s of compound 6_ (161.0 mg) were.:irradiated.at 0.03 between 8.1° and 9.5° f o r 31.5 hours.  torr  The amount of material  recovered from the reactor was 149.4 mg  (=93% recovery). A portion  of t h i s mixture (101.0 mg) was analyzed by NMR  using 0.4 ml of a  stock s o l u t i o n of nitromethane containing 228.3 mg of nitromethane per 10 ml of CDCl^ s o l u t i o n as the i n t e r n a l standard.  The  NMR  integration of the C9 v i n y l of the product 6A was used f o r the analysis. The calculated extent of reaction was  28.5%.  (For method of c a l c u -  l a t i o n see under General i n the Experimental Section.) Photolysis of 6. i n Benzene  A s o l u t i o n containing 116.6 mg of 6^ i n 100 ml of benzene was degassed and i r r a d i a t e d for 30.1 hours. vacuo, l e f t a t h i c k yellow o i l . 39.3 mg of r e s i d u a l 6^ and 49.7 mg  Removal of solvent i n  Preparative TLC of t h i s material gave (64% yield), of the a l c o h o l , 6A.  l a t t e r was washed with hexane, dried and sublimed at 0.04 104°.  The  t o r r and  Subsequent c r y s t a l l i z a t i o n from acetone-hexane gave c o l o r l e s s  192 -  p l a t e s o f 6A. ?4a  Mp Ir  . 125.0°-126.0° ( l i t .  a  126.0-126.5°).  and NMR were i d e n t i c a l t o t h o s e r e p o r t e d f o r 6A i s o l a t e d i n  t h e s o l i d s t a t e p h o t o l y s i s of 6_. P r e p a r a t i o n o f 2,3-Dicyano-l,4-benzoquinone ° 10  Commercial 2 , 3 - d i c y a n o h y d r o q u i n o n e  (8.1 g, 0.05 mole)  was suspended i n 50 m l o f C C l ^ I n a 250 m l f l a s k .  Nitrogen dioxide  (as n i t r o g e n t e t r o x i d e ) was condensed i n a r e c e i v i n g t u b e c o o l e d by l i q u i d n i t r o g e n .  The condensed l i q u i d was added i n s m a l l  p o r t i o n s t o the suspension of the q u i n o l w i t h s t i r r i n g .  The  a d d i t i o n was c o n t i n u e d u n t i l brown fumes o f n i t r o g e n o x i d e s p e r s i s t e d f o r several minutes.  S t i r r i n g was c o n t i n u e d f o r a f u r t h e r 1 hour  a f t e r w h i c h e x c e s s o x i d e s o f n i t r o g e n were removed by a s t r e a m o f n i t r o g e n gas.  The r e s u l t i n g m i x t u r e was f i l t e r e d - t o g i v e a y e l l o w  s o l i d w h i c h was c r y s t a l l i z e d from CHCl^-benzene t o a f f o r d 6.9 g ( 8 7 % y i e l d ) of g o l d e n c r y s t a l s o f 2 , 3 - d i c y a n o - l , 4 - b e n z o q u i n o n e . Mp  181-182° ( l i t .  1  0  0  178-180°).  P r e p a r a t i o n o f 4ag,8ag-Dicyano-6,7-dimethy 1,4-naphthoquinone  101  1-43.6,5,8,8ag-tetrahydro-  , J_  C r y s t a l s o f 2 , 3 - d i c y a n o - l , 4 - b e n z o q u i n o n e (4.0 g, 0.025 mole) and 100 m l o f a s o l v e n t m i x t u r e o f acetone-benzene  (1:1 V/V)  were i n t r o d u c e d i n t o a 250 m l t h r e e - n e c k e d f l a s k e q u i p p e d w i t h a  - 193 -  condenser.  The m i x t u r e was warmed and m a g n e t i c a l l y s t i r r e d u n t i l t h e  quinone d i s s o l v e d .  The s o l u t i o n was  c o o l e d t o room t e m p e r a t u r e  and 3.7 g (0.05 mole) of 2 , 3 - d i m e t h y l - l , 3 - b u t a d i e n e added. m i x t u r e was  s t i r r e d a t room t e m p e r a t u r e f o r 22 hours and t h e n  s t r i p p e d o f s o l v e n t s and e x c e s s d i e n e .  This l e f t a t h i c k o i l  p r e c i p i t a t e d upon a d d i t i o n o f l i g h t p e t r o l e u m (30°-60°). f l a s k was  The.  which  The  c o o l e d i n i c e f o r 30 m i n u t e s and the r e s u l t i n g g o l d e n  y e l l o w s o l i d was f i l t e r e d ; washed w i t h p e t r o l e u m - e t h e r (30°-60°) and dried.  T h i s gave 5.9 g (98%) o f compound _7.  I t was  crystallized  twice from acetone-petroleum e t h e r t o g i v e l a r g e , s p a r k l i n g , y e l l o w . - p l a t e s o f 7_. 101  Mp  156.5°-157.5° ( l i t .  Ir  ( K B r ) , 4.44  NMR  (C=N), 5.79  (CDC1 ) 6, 6.88 3  C8 m e t h y l e n e s ) , 1.73  157°-158°). and 5.86  (C=0), 6.24  ( c o n j . C=C)  ( s , 2H, C2 and C3 v i n y l ) , 2.71  ( s , 4H, C5  u. and  ( s , 6H, m e t h y l s ) .  P h o t o l y s i s o f J_ i n KBr  A 0.4% KBr p e l l e t o f 1_ was  irradiated.  of i r r a d i a t i o n , a new b r o a d b u t i n t e n s e peak was 2.91u  (OH).  A f t e r 0.3  observed at  I n t h e c a r b o n y l r e g i o n , t h e 5.79u peak had d e c r e a s e d  r e l a t i v e t o the 5.86u peak.  A f t e r 0.5 hour o f i r r a d i a t i o n , a  a b s o r p t i o n began t o d e v e l o p a t 5.62u. expense of the 2.91 and 5.86  new  T h i s peak i n c r e a s e d a t the  u a b s o r p t i o n s u n t i l i t became t h e more  i n t e n s e of the two c a r b o n y l peaks a f t e r a t o t a l of 18 hours of irradiation.  hour  - 194 -  I r r a d i a t i o n o f Compound X i n t h e S o l i d  State  C r y s t a l s of compound 7_ (230.4 mg) 0.01  t o r r between 19.3°  m i x t u r e w h i c h was  and 19.7°  f o r 1.5  were i r r a d i a t e d a t  hours.  The r e a c t i o n  r e t r i e v e d f r o m t h e r e a c t o r weighed 195.2  mg  (85%  recovery). To 22.0 mg  o f t h e r e a c t i o n m i x t u r e , 0.2  ml o f a s t o c k  s o l u t i o n o f benzophenone ( i n t e r n a l s t a n d a r d ) i n c h l o r o f o r m added.  GLC  a n a l y s i s of t h i s m i x t u r e was  10% OV-210 column a t 175° d e t e c t o r response determined GLC  was  c a r r i e d out on a 5' x  and a f l o w r a t e o f 160 ml/min.  V  The  f a c t o r f o r 7_ under i d e n t i c a l c o n d i t i o n s was  t o be 1.34.  The  c a l c u l a t e d % c o n v e r s i o n o f 1_ from the  a n a l y s i s o f t h e r e a c t i o n m i x t u r e was  34%.  ( F o r method of c a l c u -  l a t i o n , see under G e n e r a l i n t h e E x p e r i m e n t a l S e c t i o n ) . The r e s t o f the r e a c t i o n mixture  (172.5 mg)  was  s e p a r a t e d by p r e p a r a t i v e TLC  ( s i l i c a g e l ; 10% a c e t o n e - c h l o r o f o r m ) . r e s i d u a l 1_ and 57.3 mg  o f 7A  T h i s gave 109.2  (91% y i e l d ) .  mg  of  The y i e l d s from t h r e e  o t h e r r u n s were 98%, 94% and 87% a t c o n v e r s i o n s o f 19%, 30% and respectively.  The p r o d u c t f r o m a l l t h e r u n s was  26%  combined and  c r y s t a l l i z e d from acetone-hexane t o g i v e c o l o r l e s s c r y s t a l s of  7A.  24h  Mp  195-196° ( r e p o r t e d  Ir  ( K B r ) , 2.93  C=C)  y.  NMR J=10  (CDCl -acetone 3  188-190°).  (OH), 4.41  d ) &  6,  and 4.45  7.00  Hz, I H , C3 v i n y l ) , 5.79  (C=N), 5.87  ( d , J=10 ( d , J=1.5  (C=0) , 6.15  (conj.  Hz, I H , C2 v i n y l ) , 6.22 Hz, I H , C9 v i n y l ) , 2.80  (d, ( s , IH,  195'  -  -  OH, d i s a p p e a r s on a d d i n g D 0 ) , 2.16 ( d , J=13.5 Hz, I H , one o f t h e C6 2  m e t h y l e n e s ) , 1.92 ( d , J=13.5 Hz, I H , t h e o t h e r C6 m e t h y l e n e ) , 1.91 ( d , J=1.5 Hz, 3H, C8 m e t h y l ) , 1.21 ( s , 3H, C7 m e t h y l ) . Mass spectrum m/e p a r e n t 240. Anal. Calcd. f o r 4 C  1  H  N 1 2  2°2  :  Found : Irradiation  C  '  e 9  '">  H  »  5  -  0 4  ; » N  H-66.  C, 69.99; H, 5.00; N, 11.54.  o f P r o d u c t 7A i n KBr  The i r r a d i a t i o n o f a 0-4% KBr p e l l e t o f 7A f o r 2.5 h o u r s l e d t o new c a r b o n y l a b s o r p t i o n s a t 5.61 and 5.76 u.  After  8.4  h o u r s , t h e 5.61p C=0 was t h e most i n t e n s e o f t h e t h r e e c a r b o n y l peaks. Irradiation  o f J_ i n Benzene A s o l u t i o n o f 242.0 mg o f compound 7_ i n 150 m l o f benzene  was degassed and p h o t o l y s e d f o r 0.5 h o u r .  P r e p a r a t i v e TLC  (silica  g e l ; 10% a c e t o n e - c h l o r o f o r m ) gave 121.4 mg o f r e s i d u a l 1_, 89.8 mg of p r o d u c t 7A (74% y i e l d ) and 8.3 mg o f compound 7B ( 7 % y i e l d ) . mp  and s p e c t r a o f 7A were i d e n t i c a l t o t h o s e of.7A i s o l a t e d  t h e s o l i d s t a t e p h o t o l y s i s o f ]_. Ir NMR  Compound 7_B had m.p.  The  from  156-158°.  ( K B r ) , 4.44 and 4.46 (C=N); 5.90 (C=0) u. (CDC1 ) 6, 7.44 ( d , J=10 H z , l H , C2 v i n y l ) , 6.41 ( d , J=10 Hz, 3  I H , C3 v i n y l ) , 2.56 ( s , 2H, C6 or" C9 m e t h y l e n e s ) , 2.45 ( d , J=15 Hz, I H , one o f t h e C 9 orC6 m e t h y l e n e s ) , 1.72 ( d , J=15 Hz, t h e o t h e r C9 o r C6 m e t h y l e n e ) , 1.5.6 ( s , 3H, C8 m e t h y l ) , 1.38 ( s , 3H, C7 m e t h y l ) .  - 196 -  Mass spectrum m/e parent 240. A possible structure f o r J7B_ i s discussed i n the text.  Preparation of 4ag-8ag-Dicyano-5a,8a-dimethyl-4ag,5,8 ,8ag-tetrahydro1,4-naphthoquinone^^*, j j  A s o l u t i o n of 1.5 g (0.009 mole) of 2,3-dicyano-l,4benzoquinone was dissolved i n 60 ml of benzene-acetone 1.5 g of trans,trans-2,4-hexadiene added.  (1:1) and  The mixture was  magnetically s t i r r e d at room temperature for 21 hours.  The r e s u l t i n g  yellow s o l u t i o n was stripped of solvents and r e s i d u a l diene.  The  s o l i d was c r y s t a l l i z e d from acetone-hexane to give 1.4 g (65% y i e l d ) of sparkling, pale yellow c r y s t a l s . 2 Ah Mp  153°-154° ( l i t .  155°-156°).  Ir  . (KBr), 4.45 (CsN), 5.78 and 5.88 (C=0), 6.24 (conj. C=C) y.  NMR  (CDC1 ) 6, 6.94 (s, 2H, C2 and C3 v i n y l s ) , 5.62 ( s , 2H, C6 and 3  C7 v i n y l s ) , 3.09 (q, J=8 Hz, 2H, C5 and C8 methines), 1.29 (d, J=8 Hz, 6H, C5 and C6 methyls). I r r a d i a t i o n of B_ i n KBr A 0.4% KBr p e l l e t of J3_ was i r r a d i a t e d .  The i r taken  after 1.3 and 4.3 hours, r e s p e c t i v e l y showed no new peaks.  However,  a f t e r 24 hours of t o t a l i r r a d i a t i o n , the 5.87y C=0 had grown i n i n t e n s i t y r e l a t i v e to the 5.78y C=0.  - 197- -  A.  I r r a d i a t i o n of Adduct SL i n the S o l i d State Crystals of adduct 8^ (172.0 mg) were photolysed  discontinuously at 0.02 of 35 hours. 166.1 mg  torr between 7.2° and 8.3° f o r a t o t a l  Recovery of material from the reaction stage was  (97%).  Preparative TLC ( s i l i c a g e l , 30% ethyl acetate-  benzene) gave 130.3 mg of r e s i d u a l JJ, and 27.0 mg thick o i l which s o l i d i f i e d on standing. runs were 74% and 65% r e s p e c t i v e l y . was combined  (75% y i e l d ) of a  The y i e l d s from two other  The product from a l l runs  and c r y s t a l l i z e d twice from ether-petroleum ether with  a few drops of acetone.  The r e s u l t i n g c o l o r l e s s c r y s t a l s , 8A, had  24b mp  138-139°  Ir  (KBr), 4.45  NMR  (lit.  137.5°-139°).  (C=N), 5.90  (CDC1 ) 6, 7.54 3  IH, C3 v i n y l ) , 4.77  (C=0), 6.28  (d, J=10 Hz, IH, C2 v i n y l ) , 6.27  (d, J=10  (d, J=3.5 Hz, IH, C8 methine), 3.18  IH, C7 methine), 2.88  Hz,  (d, J=3.5 Hz,  (q, J=7 Hz, IH, C6 or C9 methine), 2.64 (q,  J=8 Hz, IH, C6 or C9 methine), 1.39 0.94  (conj. C=C) y.  (d, J=7 Hz, 3H, C6 or C9 methyl)  (d, J=8 Hz, 3H, C6 or C9 methyl).  Mass spectrum m/e  parent 240. \  B.  I r r a d i a t i o n of 8. i n the S o l i d State and Determination of the Extent of Reaction Crystals of J3 (147.5 mg) were i r r a d i a t e d discontinuously  as i n A above at a vacuum of 0.03 t o r r and temperatures between 7.5° and 9.0° f o r a t o t a l of 31 hours.  (The reactor was positioned  -  198 -  at the same distance from the lamp as i n A). m a t e r i a l from the reactor was s o l u t i o n of nitromethane  94%.  The recovery of  A 0.3 ml a l i q u o t of a stock  containing 228.3 mg of CH^M^  per 10 ml of  deuterochloroform s o l u t i o n was added to 32.5 mg of the reaction mixture.  This mixture was  analysed q u a n t i t a t i v e l y by NMR  using  the integrations of the C2 and C3 Hs of 8^ at 6.946 r e l a t i v e to those of the methyl resonance of nitromethane, standard.  the i n t e r n a l  Using the method outlined under General i n the  Experimental Section, the r e s i d u a l E[ i n the 32.5 mg of mixture was found to be 26.0 mg.  The extent of r e a c t i o n was  thus 20%.  To check the accuracy of the method, 33.2 mg of authentic (3 and 0.3 ml of the i n t e r n a l standard stock s o l u t i o n were analysed as above. 33.1 mg.  The amount of j8 as calculated from the NMR The accuracy of t h i s method was  thus  analysis was  >99%.  I r r a d i a t i o n of Adduct jj i n Benzene i  -  A solution containing 131.7 mg of compound 8^ i n 100 ml of benzene was degassed and photolysed, discontinuously f o r 3 hours. The r e a c t i o n was followed by TLC benzene).  ( s i l i c a g e l ; 30% e t h y l acetate-  ' The i r r a d i a t e d s o l u t i o n was  concentrated and subjected  to column chromatography ( s i l i c a g e l ; 30% e t h y l Combination  acetate-benzene).  of the f i r s t s i x f r a c t i o n s followed by removal of solvent  gave 20.0 mg of r e s i d u a l 8^.  Fractions 7-14  gave 67.8 mg  (60% y i e l d )  - 199  of a p a l e y e l l o w o i l ,  8A, which was  -  crystallized  t w i c e from e t h e r -  p e t r o l e u m e t h e r w i t h a few drops of a c e t o n e .  24h Mp  141.5°-142.5°  I t s i r and NMR  (lit.  137.5°-139°).  were i d e n t i c a l t o t h o s e o f s o l i d  Preparation of  state product  8A.  2,3,4a&6,7,8ag-Hexamethyl-4a,5,8,8a-tetrahydro-l,4-  . „. . 102 Q naphthoquinone , 9_ A m i x t u r e of 2.0 g (0.024 mole) o f 2 , 3 - d i m e t h y l - l , 3 b u t a d i e n e , 1.61  g (0.098 mole) of duroquinone and a few  crystals  of hydroquinone were h e a t e d i n a s e a l e d P y r e x tube a t 197° f o r 23 hours.  The c o n t e n t s o f the tube were washed out w i t h c h l o r o f o r m .  Subsequent which was 1.36  r e m o v a l o f t h e s o l v e n t and e x c e s s d i e n e l e f t crystallized  t h r i c e from p e t r o l e u m e t h e r  a  solid  (68°).  This  gave  g (56% y i e l d ) o f l a r g e , p a l e - y e l l o w c r y s t a l s of 9/. 10?  Mp  113-114°  Ir  ( K B r ) , 5.97  NMR  (lit.  115-117°).  (C=0), 6.15  ( c o n j . C=C)  y.  ( C C 1 ) 6, 2.70-1.50 (m, 4H, C5 and C8 m e t h y l e n e s ) , 1.86 4  C6 and C7 m e t h y l s ) , 1.60  ( s , 6H, C2-and C3 m e t h y l s ) , 1.10  ( s , 6H,  ( s , 6H,  C9 and C10 m e t h y l s ) . I r r a d i a t i o n of 9_ i n KBr  A 0.4% f o l l o w e d by i r .  KBr p e l l e t o f 9^was i r r a d i a t e d and the r e a c t i o n  A f t e r 3 hours of i r r a d i a t i o n , the spectrum showed  a new b r o a d peak a t 2.90y i n d i c a t i v e of OH and two new a b s o r p t i o n s a t 5.64  and 5.83  y respectively.  carbonyl  _  200 _  I r r a d i a t i o n of 9. l n the Solid State In a s e r i e s of reactions,  50-80 mg of 9^were i r r a d i a t e d  at 0.03-0.05 t o r r between - 2 6 ° to - 2 3 ° for periods ranging from 1.5 to 24 hours. all  The recovery of material from the reactor, i n  cases was >78%.  A l l the reaction mixtures were combined and  separated by column chromatography ( s i l i c a g e l ; 8% e t h y l acetatebenzene) .  The order of e l u t i o n was 9_, 915, and j)A.  Compound 9_ was  c r y s t a l l i z e d from petroleum ether and shown by m.p. i r and NMR to be residual starting material.  Product 9B was p u r i f i e d by short path  vacuum d i s t i l l a t i o n at 0.01 t o r r and 6 5 - 7 0 ° using a Kugelrohr. Mp* Ir  24.5-26.0°. (KBr), 5.67, 5.84 (C=0) y .  NMR (CC1 4 ) 6, 2.44 (q, J=7.5 Hz, IH, C7 methine), 2.02 (m, 3H, C l methine and C4 methylenes), 1.68 (m, 6H, v i n y l methyls), 1.21 (s, 3H, methyl), 1.03 (s, 3H, methyl), 1.03 (d, J=7.5 Hz, 3H, C7 methyl), 0.95  (s, 3H, methyl). Product 9A c r y s t a l l i z e d from petroleum ether as colorless  crystals. Mp  101.0-102.0°  (lit.24a  101.0-102.0°).  Ir  (KBr), 2.87 (OH), 6.03 (C=0) y .  NMR (CCl^) 5, 5.38 (m, IH, C9 v i n y l ) , 2.24 (s, IH, disappears on adding D 2 0 , OH), 1.85 (d, J=2 Hz, 3H, C3 methyl), 1.76 (d, J=13 Hz, IH, one of the C6 methylenes), 1.08 (s, 3H, methyl), 0.97 (d, J=13 Hz, IH, the other C6 methylene), 0.85 (s, 3H, methyl), 0.80 (s, 3H, methyl).  - 201 ~  The above spectra reported for 9A and JJB were i d e n t i c a l to authentic samples prepared by photolysis of adduct 9^ i n benzene.  Authentic Samples of Products i!A and  33.  Samples of 9A and £B f o r comparative purposes and for the determination of the detector response factors (below) were kindly supplied by Mr. J.P. Louwerens to whom the author i s g r a t e f u l .  I r r a d i a t i o n of 9. i n the S o l i d State.  Quantitative GLC  Analyses were c a r r i e d out on a 5' x V  column of 20% DEGS  on 60/80 Chromosorb W operated at 150° and 150 ml/min. times were 16.4,  19.0  and 22.0 minutes for 9B_,  Analyses  Retention  and 9A r e s p e c t i v e l y .  The detector response f a c t o r s f o r 9B_, 9_> and 9A were determined t o ' be 1.5,  1.2 and 1.3 r e s p e c t i v e l y , using a solution, containing  weighed amounts of the three compounds and an aliquot.of a stock s o l u t i o n of biphenyl as the i n t e r n a l standard.  (For method of  c a l c u l a t i o n s , see under General i n the Experimental Section). Crystals of 9_ (49.3 mg) were i r r a d i a t e d between -34.0° and -33.5° for 8 hours.  A 0.5 ml a l i q u o t of the stock s o l u t i o n of  biphenyl (173.2 mg per 10 ml of benzene solution) was added to the reaction mixture and the mixture analysed by GLC.  Results of this  and other runs are tabulated i n the text under Results and Discussion.  - 202 -  P h o t o l y s i s of 9_ i n D i e t h y l E t h e r Below t h e E u t e c t i c Temperature These r e a c t i o n s were c a r r i e d out i n t h e a p p a r a t u s f o r low t e m p e r a t u r e s o l u t i o n r e a c t i o n s d e s c r i b e d under G e n e r a l i n t h e Experimental Section. A s o l u t i o n c o n t a i n i n g 86.8 mg d i e t h y l e t h e r was for  6.5  hours.  degassed  and p h o t o l y s e d , between -31.5° and -29.0°  The r e a c t i o n m i x t u r e was  b i p h e n y l as i n t e r n a l s t a n d a r d . r u n s , see  of £ i n 40 m l of anhydrous  a n a l y z e d by GLC  using  F o r t h e r e s u l t s of t h i s and o t h e r  text.  P r e p a r a t i o n of 2,3,4ag,5a,8a,8ag-Hexamethyl-4ag,5,8,8ag-tetrahydro24b 1,4-naphthoquinone  N  , JLO,  A m i x t u r e o f 1.6 of  g (9.7 m i l l i m o l e ) o f d u r o q u i n o n e ,  2.0  t r a n s , t r a n s - 2 , 4 - h e x a d i e n e and a few c r y s t a l s o f hydroquinone  h e a t e d i n a s e a l e d P y r e x tube a t 143°  f o r 46 h o u r s .  t h e s o l i d was washed out w i t h a c e t o n e .  After  The m i x t u r e was  s o l i d p o r t i o n (0.611 g) was  s u b l i m e d a t 0.03  s u b s e q u e n t l y i d e n t i f i e d by m.p., quinohe.  The f i l t r a t e was  s t r i p p e d of  (<0.08 mm)  The o f f - w h i t e  t o r r and 150° t o be  The  and  durohydro-  c o n c e n t r a t e d and c o o l e d f i r s t t o room  t e m p e r a t u r e and t h e n i n i c e . quinone.  i r and NMR  were  cooling,  s o l v e n t and a p p r o x i m a t e l y 100 ml o f p e t r o l e u m e t h e r added. m i x t u r e was warmed w i t h s w i r l i n g and t h e n f i l t e r e d .  g  T h i s gave 250.3 mg o f r e s i d u a l  The mother l i q u o r was  duro-  chromatographed on 30 g of s i l i c a g e l  u s i n g benzene as e l u e n t .  F r a c t i o n s were checked by  GLC  - 203  (7  1  x V  min.)'  -  column of 20% DEGS on 60/80 Chromosorb W at 170° and 200 ml/ The f r a c t i o n s  containing duroquinone and 10 were concentrated  and separated by GLC. pale yellow o i l .  This gave 311.3 mg  I t was  (15% y i e l d ) of 10 as a  c r y s t a l l i z e d twice from hexane to give ?4h  material melting at 52-54° (reported Ir NMR  (KBr), 5.91  and 6.00  (CDC1 ) 6, 5.44 3  (C=0), 6.13  (conj. C=0)  y.  (s, 2H, C6 and C7 v i n y l s ) , 2.02  C5 and C8 methines), 1.91  (q, J-8  (s, C2 and C3 methyls), - 1.27  C4a and C8a methyls), 1.01 Irradiation  47-50°).  Hz,  (s, 6H,  (d, J=8 Hz, 6H, C5 and C8 methyls).  of 10 i n KBr  A 0.4% KBr p e l l e t of 10 was  irradiated.  the p e l l e t was recorded at hourly i n t e r v a l s  The i r of  f o r the f i r s t 2 hours  and then at longer i n t e r v a l s up to 17 hours t o t a l time of i r r a d i a t i o n . There were no changes i n the spectrum f o r the f i r s t 2 hours.  However,  a f t e r 6 hours of t o t a l i r r a d i a t i o n , broadening i n the 5.6-5.78 y region became apparent.  The i r recorded a f t e r 17 hours of  i r r a d i a t i o n showed two new carbonyl stretches at 5.70  Irradiation  and 5.76  y.  of 10 i n the Solid State A solution  containing 56.6 mg of 10_ i n a cet one-hexane was  slowly evaporated on the reaction stage and l e f t overnight. observed that no c r y s t a l l i z a t i o n had occurred.  The apparatus  I t was was  assembled as f o r a normal run except that the sample was neither  - 204; -  cooled nor i r r a d i a t e d .  I t was l e f t under vacuum thus f o r an hour.  The r e a c t i o n stage was subsequently cooled, down to -9.5° and the sample kept under vacuum and at t h i s temperature f o r 6 hours. was subsequently l e f t under vacuum overnight.  It •  This procedure  allowed 10 to c r y s t a l l i z e out on the reaction stage.  The sample was  i r r a d i a t e d at 0.03 t o r r between -9.9° and -9.1° f o r a t o t a l of 14 hours.  The m a t e r i a l which was recovered from the reactor weighed  53.4 mg (95% recovery). The i r r a d i a t e d sample was checked by TLC ( s i l i c a g e l ; 15% e t h y l acetate-benzene), GLC (7' x V  column of 20% DEGS on  60/80 Chromosorb W, at 170° and 150 ml/min.), i r and NMR. A l l analyses showed the presence of only 10. In a s i m i l a r procedure 43.2 mg of 10_ evaporated from petroleum ether was i r r a d i a t e d at 0.04 torr and -1.4° to -0.5° f o r 13 hours.  Analyses as above again showed no r e a c t i o n had occurred.  Preparation of 2,3,4ag,56,86,8ag-Hexamethyl-4a,5,8,8a-tetrahydrol,4-naphthoquinone k, jy^ 24  A mixture of 3.20 g (19.5 millimoles) of duroquinone, 4 g of trans,trans-2,4-hexadiene and a few c r y s t a l s of hydroquinone was heated at 185° i n a sealed Pyrex tube f o r 22.4 hours. dark-brown mixture was washed out with chloroform. solid torr).  the r e s u l t i n g  An i n s o l u b l e  (1.6 g) was f i l t e r e d and p u r i f i e d by sublimation (150°, 0.03 I t had mp 228-229° and was i d e n t i f i e d by infrared,NMR and  - 205 -  84 elemental a n a l y s i s to be durohydroquinone, mp  233°.  liquor was concentrated and subjected to column  The mother  chromatography  on 64 g of n e u t r a l alumina a c t i v i t y grade 1 from M. Woelm.  I t was  eluted f i r s t with benzene and approximately 110 ml c o l l e c t e d and shown by GLC ^(5' x V  s t a i n l e s s s t e e l , 20% DEGS on 60/80 Chromosorb  W; 130°, 180 ml/min) to contain none of the desired Diels-Alder adduct.  The e l u t i n g solvent was changed to 15% e t h y l acetate-benzene  and subsequent f r a c t i o n s checked by GLC.  The f r a c t i o n s containing  adduct 11 were combined and stripped of solvents. o i l s o l i d i f i e d on standing to give 160 mg  The r e s u l t i n g  (3% y i e l d ) of compound 11.  It was c r y s t a l l i z e d twice from petroleum-ether to give pale-yellow ?4h rods of 11 melting at 104-105° ( l i t . Ir  (KBr) 5.99  (C=0), 6.12  NMR  (CDC1 ) 6, 5.42 3  methines), 1.97  (conj. C=C)  103-104°). y.  (s, 2, v i n y l s ) , 2.85  (s, 6, C2 and C3  (q, 3=7 Hz, 2, C5 and C8  methyls), 1.13  (s, 6, C4a and C8a  methyls), 0.93 (d, J=7 Hz, 6, C5 and C8 methyls). I r r a d i a t i o n of Compound 11 i n KBr A 0.4% KBr p e l l e t of compound LL was i r r a d i a t e d and the reaction monitored by i n f r a r e d .  (X >^ 340  nm)  After 0.5 hour, the reaction  was complete as judged by the disappearance of a moderately intense peak of 11 at 7.98y. at 2.88y.  A f a i r l y sharp and intense peak had developed  In a d d i t i o n , there were new carbonyl absorptions at 5.67,  5.85 and 6.05  y, r e s p e c t i v e l y .  Further i r r a d i a t i o n up to 1.5 hours of  - 206 -  t o t a l i r r a d i a t i o n time produced no further changes i n the spectrum. A.  Irradiatibn of Compound 11 i n the S o l i d State Crystals of compound 11 (56.9 mg) were i r r a d i a t e d (X >_ 355 nm)  at 0.005 t o r r and between -32.4 and - 3 1 . 7 °  for 5.6 hours.  The  reaction mixture was washed off the r e a c t o r ' s cavity with chloroform, stripped of solvent and dried i n vacuo. weighed 49.2 mg (86% recovery). (5 mg) was used i n GLC analysis  The recovered material  A small amount of t h i s mixture (5' x V  s t a i n l e s s s t e e l column of 20%  DEGS on A/W Chromosorb W; 60/80 mesh) at 1 5 0 ° and 100 ml/min.  It showed  two peaks with retention times of approximately 16 and 22 minutes, respectively.  The r e s t of the reaction mixture (44.2 mg) was  subjected to preparative TLC ( s i l i c a g e l ; 8% ethyl  acetate-benzene).  This gave 11.6 mg of a white s o l i d (lower band) and 25.9 mg of an o i l . The infrared and NMR spectra of these two samples showed that the s o l i d was enone-alcohol 11A and the o i l ene-dione 11B.  The s t a r t i n g  material 11 which has the same Rf (TLC) and the same GLC retention time as product 11B was found to be absent from the NMR sample of 11B. The conversion of s t a r t i n g material to photoproducts i s complete.  thus  The combined i s o l a t e d y i e l d of the two products i s 85%  and the 11A:11B r a t i o i s  1:2.  In another run, 70.4 mg of c r y s t a l s i r r a d i a t e d at 0.005 t o r r and between - 3 1 . 6 °  of adduct 11 were and - 2 7 . 3 °  for 5 hours.  The recovered m a t e r i a l from the reactor weighed 60.8 mg (86% recovery).  -  207 -  A portion of t h i s material (29-0 mg) was set aside for GLC a n a l y s i s . The rest of the reaction mixture was separated by preparative TLC ( s i l i c a g e l ; 8% e t h y l acetate-benzene)  and shown by NMR to contain only  photoproducts 11A and 11B. An aliquot (0.2 ml) of a stock s o l u t i o n of i n t e r n a l standard (173.2 mg of biphenyl i n  10 ml of benzene) was added to the  29.0 mg of reaction mixture and the r e s u l t i n g s o l u t i o n analyzed by GLC (5' x V  column of 20% DEGS at 1 5 0 ° and 150 ml/min) .  The peak  areas for biphenyl,11B and 11A were calculated for each of 4 i n j e c t i o n s . The r e l a t i v e areas (area of sample peak/area of biphenyl peak) were c a l c u l a t e d and the average r e l a t i v e area for each of the two peaks found.  The detector response  factors  GLC conditions were 1.9 and 1.7,  for 11B and 11A under i d e n t i c a l  respectively.  Using these values,  the average r e l a t i v e areas and the weight of i n t e r n a l standard i n the GLC mixture, the weight of each of the two products was calculated as outlined under General i n the Experimental Section.  This  analysis  showed, that the 29.0 mg sample of reaction mixture contained 8.4 mg of enone-alcohol 11A and 16.7 mg of ene-dione 11B.  The combined  GLC y i e l d of the two products i s thus 86% and the 11A:11B r a t i o is  1:2.  B.  Low Conversions of Adduct JLL Since the s t a r t i n g material 11 and one of i t s  photoproducts,  namely 11B could not be separated by GLC or TLC under the conditions  - 208 -  t r i e d , the analyses of reaction mixtures containing 11, 11A and 11B were c a r r i e d out as f o l l o w s :  the reaction mixture was f i r s t  separated .  by TLC into two f r a c t i o n s ,  one containing s o l e l y 11A and the other  containing product 11B and residual s t a r t i n g material 11.  The LI +  11B mixture was then analyzed by quantitative NMR using the integrated peak area of the C2 and C3 methyl resonance of jLl at 61.97 and the peak area of the resonances standard.  of added biphenyl as i n t e r n a l  This analysis allowed.for the c a l c u l a t i o n of the weight  of r e s i d u a l 11 i n the reaction mixture.  The y i e l d of photoproduct  11B i s then e a s i l y found by subtracting the calculated weight of r e s i d u a l 11 from the 11^ + 11B mixture.  Below i s one of the low  conversion runs which was analyzed by t h i s method. C r y s t a l s of compound 11 (53.6 mg) were i r r a d i a t e d at 0.005 t o r r between - 3 2 . 1 °  and - 3 1 . 5 °  for 2 hours.  The weight of recovered  reaction mixture from the reactor was 49.1 mg (92% recovery). Preparative TLC ( s i l i c a g e l ; 8% e t h y l acetate-benzene) gave 6.4 mg of enone-alcohol 11A and an upper band m a t e r i a l of 29.5 mg. C r y s t a l l i z e d biphenyl (8.4 mg) was added to the upper band material to serve as the i n t e r n a l standard.  The mixture was dissolved i n  chlorof orm-d and analyzed quantitatively by NMR. The ten protons of biphenyl integrated for 39.5 and the s i x protons of 11 integrated  for  26. . Using the formula given under General i n the Experimental Section, the r e s i d u a l s t a r t i n g material 11 i n the sample was calculated to be 15.8 mg.  The conversion of 11 to products i s thus ,  56% and the weight of product 11B i s 13.7 mg.  The combined y i e l d  - 209 -  of products 11A and JIB by t h i s analysis i s again 1:2.  i s 81% and the l l A t l l B  ratio  The r e s u l t s of s i m i l a r runs are given i n the text.  The enone-alcohol product from a l l the runs was combined and c r y s t a l l i z e d from petroleum-ether to give c o l o r l e s s rods of 11A melting at 1 5 8 - 1 5 9 ° Ir  (lit.24b  156.5-157°C).  (KBr) 2.94 (OH), 6.04 (C=0) and 6.15 (conj. C=C) y .  NMR (CDC10) 6, 5.92 (m, 1, v i n y l ) , 2.63 (dd, J , =3 Hz, o o,/  „ = 3 Hz, /,o  1, C7 methine), 2.57 (s, 1, OH, disappears on adding D 2 0 ) . 2.23 (m, 1, C6 methine), 1.91 (d, J<2 Hz, 3, C3 methyl), 1.82 (d, J<2 Hz, 3, C2 methyl), 1.78 (d, J<_2 Hz, 3, C9 methyl), 0.87 (s, 3, C5 methyl), ' 0.77  (s, CIO methyl), 0.75 (d, J=7 Hz, C6 methyl).  Mass spectrum m/e parent 246. The above spectra were i d e n t i c a l to those of 11A i s o l a t e d from the 24b photolysis of adduct 11 i n benzene A l l the upper band materials from preparative TLC were combined and photolysed for 0.3 hours to photolyse r e s i d u a l 11. The r e s u l t i n g mixture was separated by preparative TLC (8% ethyl acetatebenzene) .  The o i l (upper band material) was assigned the structure  11B based on the following spectra Ir  data:  (Film), 5.64 and 5.83 (C=0) y.  NMR (CDC13) 6, 6.04 (dd, J 2 3 = 1 0 Hz, J 3 (dd, J  =10 Hz, J  4  =5.5 Hz, 1, C3 v i n y l ) , 5.59  ,=1.5 Hz, 1, C2 v i n y l ) , 2.82 (q, J=7.5 Hz, 1,  C7 methine), 2.26 (m, 1, C4 methine), 1.15 (s, C8 methyl), 1.15 (d, J=7.5 Hz, C7 methyl), 1.13 (s, C l methyl), 1.11 (d, J=7.5 Hz, C4 methyl), 1.09 (s, methyl), 1.04 (s, methyl).  - 210 -  Mass spectrum m/e parent 246. The i n f r a r e d and NMR spectra were i d e n t i c a l to those of 11B i s o l a t e d ' 24b from the photolysate of 11 i n benzene I r r a d i a t i o n of Enone-Alcohol J L I A i n KBr  A 0.4% KBr p e l l e t of photoproduct 11A was i r r a d i a t e d 355 nm) continuously f o r 2 hours.  (X >^  The i n f r a r e d spectrum of the  i r r a d i a t e d p e l l e t was i d e n t i c a l to that of 11A.  - 211 -  BIBLIOGRAPHY (1)  (a) J . C . D . Brand and J . C . Speakman, "Molecular Structure", Edward Arnold Publishers L t d . , London, 1964, p.  210.  (b) G.H. Stout and L . H . Jensen, "X-ray Structure Determination", Macmillan C o . , New York, N.Y. 1960. (c) M . J . Buerger, " C r y s t a l Structure A n a l y s i s " , Wiley and Sons, New York, N.Y. 1960. (2)  (a) J . M . Thomas and J . O . Williams, "Progress i n Solid State Chemistry", V o l . 6, H. Reiss and J . O . McCaldin, E d . , Pergamon Press, Oxford, 1961, p. 119-154. (b) J . M . Thomas, Adv. C a t a l . , 19, 202 (1969). (c) J . M . Thomas,' Chem. B r i t . 6, 60 (1970). (d) J . M . Thomas, P h i l . Trans. R. Soc. Lond., A, V o l . 277, 251 (1974). (e)  l . C . Paul and D.Y. C u r t i n , Accounts Chem. Res.,  and references  6_, 217 (1973)  22b, 30, 32 and 40 t h e r e i n .  (3) D. H u l l , "Introduction to D i s l o c a t i o n s " , Pergamon Press, New York, N.Y.,  1965.  (4) H.G. van Bueren, "Imperfections N.Y.,  in Crystals",  Interscience,  New York,  1960.  (5) W. Dekeyser, " R e a c t i v i t y of S o l i d s " ,  J . H . de Boer, W.G. Burgers,  E.W. Gorter, J . P . F . Huese and: G.C.A. Schuit, E d . , E l s e v i e r Publishing C o . , New York, N . Y . , 1961, p.  376.  (6) "Physics and Chemistry of the Organic Solid State", V o l . 1, D. Fox, M.M. Labes and A. Weissberger, 1963, ch. 3, 4 and 5.  E d . , Interscience,  New York, N . Y . ,  \  - 212 -  (7) J . N . Sherwood and S.J. (8)  Thomson, Trans. Faraday S o c , 56, 1443 (1960).  (a) D.K. Ghosh and D . H . Whiffen, M o l . P h y s . , 2_, 285 (1959). (b) W.E. Gibbs and R . L . Van Deusen, J . Polymer S c i . , 54, 51 (1961). (c) I. Miyagawa and W. Gordy, J . Chem. P h y s . , 30, 1590 (1959). (d) H.M. McConnell, C. H e l l e r , T. Cole and R.W. Fessenden, J . Am. Chem. S o c , 82, 766 (1960).  (9)  (a) I. Norman and G. Porter, Proc. Roy. Soc. (London), A230, 399 (1955). (b) J.W. Breitenbach and H. Frittum, J . Polymer S c i . , 29, 565 (1956).  (10) J . P . McCullough, H . L . Finke, J . F . Messerly,  S.S. Todd, T . C . Kincheloe,  and G. Waddington, J . Phys. Chem., 61, 1105 (1957). (11) M.D. Cohen, R. Cohen, M. Lahav and P . L . N i e , J .  Chem. Soc. Perkin  Trans. I I , 1095, (1973). (12)  (a) M.D. Cohen and G.M.J. Schmidt, J .  Chem. S o c , 1996 (1964).  (b) G.M.J. Schmidt, "Reactivity of the Photoexcited  Organic  Molecule", Interscience, New York, N.Y. 1967, p. 227. (13)  (a) M.D. Cohen, Angew. Chem. Int. Ed. E n g l . , 14, 388 (1975). (b) E . J . Baum, "Excited State Chemistry", J . N . P i t t s , J r . , Ed, Gordon and Breach, New York, N.Y. 1970, p. 121.  (14) D. Goode, Y . Lupien, W. Siebrand, D . F . W i l l i a m s , J . M . Thomas and J . O . Williams, Chem. Phys. L e t t . , (15)  25, 308 (1974).  (a) J . O . Williams and J . M . Thomas, Trans. Faraday S o c , 63, 1720 (1967). (b) J . M . Thomas and J . O . Williams, Chem. Commun., 432 (1967).  - 213 -  (16) (a) D . P . Craig and P. S a r t i - F a n t o n i ,  Chem. Commun., 742 (1966).  (b) M.D. Cohen, Z. Ludmer, J . M . Thomas and J . O . Williams, Proc. Roy. Soc. (London), A324, 459 (1971). (c) M.D. Cohen, Z . Ludmer, J . M . Thomas and J . O . W i l l i a m s , Chem. Commun., 1172 (1969). (d) M.D. Cohen and B.S. Green, Chem. B r i t . , £ , 490 (1973). (17) G.C. Nieman and G.W. Robinson, J .  Chem. Phys., 37, 2150 (1962).  (18) M.A. El-Sayed, M.T. Wauk and G.W. Robinson, Moi. P h y s . , 5_, 205 (1962). ,  (19) G. Schuster and N . J . Turro, Tetrahedron L e t t . , (20) (a) 0. Simpson, Proc. Roy. S o c ,  2261 (1975).  (London), A238, 402 (1956).  (b) D . C . Northrop and 0. Simpson, i b i d . , A234, 136 (1956). (21) D . L . Dexter, J . Chem. Phys., 21, 836 (1953). (22) 0. D i e l s and K. A l d e r , Chem. B e r . , 62, 2362 (1929). (23) R . C . Cookson, E . Crundwell, R.R. H i l l , and J . Hudec, J .  Chem. S o c ,  3062 (1964). (24) (a) J . R . Scheffer, K . S . Bhandari, R . E . Gayler and R . A . Wostradowski, J . Am. Chem. S o c , 97, 2178 (1975) and reference 2 t h e r e i n . (b) J.R. Scheffer, Soc.,  B.M. Jennings and J . P . Louwerens, J . Am. Chem.  98, 7040 (1976).  (c) J . R . Scheffer and B.M. Jennings, Chem. Commun., 609 (1975). (25) (a) A. Padwa and R. Gruber, J . Am. Chem. S o c , 92, 107 (1970). (b) A. Padwa and W. Eisenhardt, 1  i b i d . , 93, 1400 (1971).  (c) R.A. Cormier, W.L. Schreiber and W.C. Agosta, 95, 4873 (1973).  J . Am. Chem. Soc.,  -  214 -  (d) R.A. Cormier and W.C. Agosta, i b i d . , 96_,- 618 (1974). (e) T. Hasegawa, H. Aoyama and Y. Omote, Tetrahedron L e t t . , 1901 (1975). (26) (a) P.J. Wagner, Accounts Chem. Res., 4^ 168 (1971) and references therein. (b) P.J. Wagner and G.S. Hammond, "Advances i n Photochemistry", Vol.  5, W.A. Noyes, J r . , G.S. Hammond, and J.N. P i t t s , J r . , Ed.,  Interscience, New York, N.Y., 1968, p. 21-156 and references therein. (27) (a) W. Herz and M.G. Nair, J . Am. Chem. S o c , 89, 5474 (1967). (b) S. Wolff, W.L. Schreiber, A.B. Smith, I I I , and W.C. Agosta, i b i d . , 94, 7797 (1972). (c) A.B. Smith, III, and W.C. Agosta, J . Am. Chem. S o c , 95, 1961 (1973). (d) A. Marchesini, U.M. Pagnoni and A. P i n e t t i ,  Tetrahedron L e t t . ,  4299 (1973). (28) R.R. Sauers, A.D. Rousseau and B. Byrne, J . Am. Chem. S o c , 97, 4947 (1975) and references 2-21 therein. (29) (a) R.C. Cookson, E. Crundwell and J . Hudec, Chem. Ind. (London), 1003  (1958).  (b) P. Yates and P.E. Eaton, Tetrahedron L e t t . , 5 (1960). (c) P.E. Eaton and T.W. Cole, J r . , J . Am. Chem. S o c , 86, 962, 3157  (1964).  (30) R.C. Cookson, R.R. H i l l and J . Hudec, J . Chem. S o c , 3043 (1964). (31) P.J. Wagner, A.E. Kemppainen and H.N. Schott, J . Am. Chem. Soc., 95, 5604 (1973).  - 215 -  v (32) G. Porter and P. Suppan, Trans. Faraday S o c , (33) H. Morrison, V. T i s d a l e , P . J . Soc., (34)  (a)  97, 7189  61, 1664 (1965).  Wagner and K . - C . L i u , J . Am. Chem.  (1975).  I. Kochevar and P . J .  Wagner, J . Am. Chem. S o c ,  94, 3859 (1972).  (b) R.A. Caldwell, G.W. Sovocool and R.P. Gajewski, J . Am. Chem. Soc., (35)  95, 2549 (1973).  S.G. Cohen, A. Parola and G.H. Parsons, J r . ,  Chem. Rev., 73,  141  (1973) and references t h e r e i n . (36) K. Watanabe, T. Nakayama and J . Transfer,  Quart.  Spectry.  Radiative  2, 369 (1962).  (37) K. Furukawa and E . A . Ogryzlo, J . (38)  Mottl, J.  Photochem.,, 1, 163 (1972/73).  (a) D. B e l l u s , D.R. Kearns and K. Schaffner,  Helv. Chim. A c t a . ,  52, 971 (1969). (b) T. Kobayashi, M. Kurono, H. Sato and K. Nakanishi, J . Am. Chem. Soc.,  94, 2863 (1972).  (39) R . L . C a r g i l l , W.A. Bundy, D.M. Pond, A . B . Sears, J . J. (40)  S a l t i e l and  Winterle, Mol. Photochem., _3, 123 (1971) and references t h e r e i n .  (a) J . C . Dalton, K. Dawes, N . J . Turro, D.S. Weiss, J . A . and J . D . Coyle, J .  Am. Chem. S o c ,  93_, 7213  Barltrop  (1971).  (b) K. Dawes, J . C . Dalton and N . J . Turro, M o l . Photochem., _3, 71 (1971). (41)  (a) D . H . Williams, J . M . Wilson, H. Budzikiewicz and C. D j e r a s s i , J.  Am. Chem. S o c ,  85, 2091  (1963).  (b) D.H. Williams and C. D j e r a s s i , S t e r o i d s , 3_, 259 (1964). (c) C. D j e r a s s i , G. von Mutzenbecher, J . H. Budzikiewicz, J . Am. Chem. Soc.,  Fajkos, D.H. Williams and  87, 817  (1965).  -  216 -  (d) C. D j e r a s s i and L . Tokes, i b i d . ,  88, 536 (1966).  (e) L . Tokes, R . T . LaLonde and C. D j e r a s s i , J . Org. Chem., 32, 1020  (1967).  (42) J . D . Henion and D . G . I . Kingston, J . Am. Chem. S o c , 96, 2532 (1974). (43) F . P . Boer, T.W. Shannon and F.W. McLafferty, J . Am. Chem. S o c , 90, 7239 (1968). (44) F . D . Lewis, R.W. Johnson and R.A. Ruden, J . Am. Chem. Soc., 94, 4292 (1972). (45) (a) H.W. Kohlshutter, Z. Anorg. A l l g . Chem., 105, 121 (1918). (b) H.W. Kohlshutter, Naturwissenshaften,  11, 865 (1923).  (c) E . H e r t e l , Z. Electrochem., 37, 536 (1931). (46) R . E . Long, Ph.D. Thesis, U n i v e r s i t y of C a l i f o r n i a , Los Angeles, 1965. (47) (a) S . E . V . P h i l l i p s and J . T r o t t e r , Acta C r y s t a l l o g r . ,  B33, i n press.  (b) S . E . V . P h i l l i p s and J . T r o t t e r , Acta C r y s t a l l o g r . ,  B33, i n press.  (c) S . E . V . P h i l l i p s and J . T r o t t e r , Acta C r y s t a l l o g r . , B33, i n press. (48) R . C . Cookson, D.A. Cox and J . Hudec, J . (49) G.W. G r i f f i n ,  Chem. S o c , 1717 (1962).  A . F . V e l l t u r o and K. Furukawa, J . Am. Chem. S o c ,  83, 2725 (1961). (50) L . J . Bellamy, "The Infrared Spectra of Complex Molecules", 3rd E d . , Chapman and H a l l L t d . , 1975, p. 33. (51) J . M . Derfer, E . E . Pickett and C . E . Boord, J . Am. Chem. S o c , 71, 2482 (1949). (52) E.B. Reid and M. Sack, J . Am. Chem. Soc., 73, 1985 (1951). (53) J . Dekker, P . J . van Vuuren and D . P . Venter, J . Org. Chem., 33, 464 (1968).  - 217 -  (54) R. Criegee, J . Dekker and H.A. Brune, Ber. Peut. Chem. Ges., 96 2368 (1963). (55) E.E. van Tamelin, M. Shamma, A.W. Burgstahler, J . Wolinsky, R. Tamm and P.E. A l d r i c h , J . Am. Chem. Soc., 91, 7324 (1969). (56) H. Z i f f e r and I. Levin, J . Org. Chem., 34, 4057 (1969). (57) D.A. Dows i n "Physics and Chemistry of the Organic S o l i d State", Vol.  1, D. Fox, M. Labes and A. Weissberger, Ed., Interscience,  New York, N.Y., 1963, ch. 11 and references therein. (58) C.Y. Liang, S. Krimm and G.B.B.M. Sutherland, J . Chem. Phys., 25 543, 549 (1963). (59) D.A. Dows, E. whittle and G.C. Pimeritel, J . Chem. Phys., 23, 1475 (1955) and references 11 and 12 therein. (60) (a) J.K. Brown and N. Sheppard, Discuss. Faraday S o c , 9_, 144 (1950). (b) J.K. Brown and N. Sheppard, Trans. Faraday S o c , 50, 535 (1954). (61) G.M.J. Schmidt, Pure Appl. Chem., 27, 647 (1971). (62) P.E. Eaton, Accounts Chem. Res., JL, 50 (1968) and references therein. (63) P. de Mayo, Accounts Chem. Res., 4, 41 (1971) and references t h e r e i n . (64) J . Dekker, F.J.C. Martins, J.A. Kruger and A.J. Goosen, Tetrahedron Lett., 3721 (1974). (65) (a) G.S. Hammond, C A . Stout and A.A. Lamola, J . Am. Chem. S o c , 86, 3103 (1964). (b) H. Morrison, H. C u r t i s and T. McDowell, i b i d . , 88, 5415 (1966). (66) (a) A.A. Lamola, Photochem. Photobiol., ]_, 619 (1968). (b) R. Lisewski and K.L. Wierzchowski, i b i d . , 11, 327 (1970).  -  2 1 8  -  (67) S . E . V . P h i l l i p s and J . T r o t t e r , Acta C r y s t a l l o g r . ,  B32, 3098 (1976).  (68) A. Bondi, J . Phys. Chem., 68, 441 (1964). (69)  (a) D.H. Williams and I. Fleming, "Spectroscopic Methods i n Organic Chemistry", 2nd E d . , McGraw-Hill (UK) L t d . , Maidenhead, Berkshire, England, 1973, p. 96. (b) R.M. S i l v e r s t e i n and G . C . Bassler, "Spectroscopic Methods i n Organic Chemistry", 2nd E d . , John Wiley and Sons I n c . , New York, N . Y . , 1967, p. 118.  (70) N.H. Werstiuk and R. T a i l l e f e r , Can. J .  Chem., 48, 3966 (1970).  (71) B.M. Jennings, Ph.D. Thesis, U n i v e r s i t y of B r i t i s h Columbia, 1975. (72) R.B. Woodward and R. Hoffman, "The Conservation of O r b i t a l Symmetry", Academic Press, New York, N.Y. 1970. (73) S . E . V . P h i l l i p s and J . T r o t t e r , Acta C r y s t a l l o g r . ,  i n press.  (74) S . E . V . P h i l l i p s and J . T r o t t e r , Acta C r y s t a l l o g r . , B32, 3101 (1976). (75) S . E . V . P h i l l i p s and J . T r o t t e r , Acta C r y s t a l l o g r . , (76)  i n press.  (a) L . Pasteur, Ann. Chim. et p h y s . , 24, 442 (1848). (b) K. Vogler and M. K o f l e r , Helv. Chim. A c t a . , 39, 1387 (1956). (c) R . C . F e r r e i r a , Nature', 171, 39 (1953).  ,  (d) E . Havinga, Biochim. et Biophys., Acta, 13, 171 (1954). (77) S . E . V . P h i l l i p s and J . T r o t t e r , Acta C r y s t a l l o g r . , B32, 3088 (1976). (78) P . J . Wagner, P . A . Kelso, A . E . Kemppainen and R.G. Zepp, J . Am. Chem. Soc.,  94, 7500 (1972)  and references 2-4 and 8 t h e r e i n .  (79) S . E . V . P h i l l i p s and J . T r o t t e r , Acta C r y s t a l l o g r . ,  B32, 3091 (1976).  (80) A . F . Thomas and B. Willhalm, Helv. Chim. A c t a . , 50, 826 (1967).  - 219 -  (81)  (a) J . C . D . Brand and D.G'. Williamson, Advan. Phys. Org. Chem., 1 365 (1963) and references t h e r e i n . (b) J . C . D . Brand and D.G. Williamson, Discuss.  Faraday S o c ,  35,  184 (1963). (c) D.A. Haner and D.A. Dows, J . Mol. S p e c t r o s c , 34, 296  (1970).  (d) C T . L i n and D . C . Moule, i b i d . , 38, 136 (1971). (82)  (a) M.A. Winnik, A. Lemire, D.S. Saunders and C K . Lee, J . Soc.,  Am. Chem.  98, 2000 (1976).  (b) M.A. Winnik, S.N. Basu, C K . Lee and D.S. Saunders, i b i d . , 98, 2928 (1976). (83)  J . T . Edward, J .  Chem. Educ., 47, 261 (1970).  (84)  "Handbook of Chemistry and P h y s i c s " , 52nd E d . , Chemical Rubber C o . , Cleveland, Ohio, 1971-1972.  (85) D. Rabinovich and G.M.J. Schmidt, J .  Chem. S o c ,  B. , 144 (1967).  (86)  S . E . V . P h i l l i p s and J .  T r o t t e r , Acta C r y s t a l l o g r . ,  i n press.  (87)  S . E . V . P h i l l i p s and J .  T r o t t e r , Acta C r y s t a l l o g r . ,  B32, 3095 (1976).  (88) D.R. Arnold, "Advances i n Photochemistry", V o l . 6, W.A. Noyes, G.S. Hammond and J . N . P i t t s , N . Y . , 1968, p. (89)  Jr.,  E d . , Interscience,  T r o t t e r , Acta C r y s t a l l o g r . ,  (90) H. S t e r n l i c h t , G . C Nieman and G.W. Robinson, J .  (91) J .  New York,  301.  S . E . V . P h i l l i p s and J .  1326  Jr.,  B32, 3095 (1976).  Chem. Phys.,  38,  (1963).  Kaiser, G. Wegner and E.W. F i s c h e r , I s r .  J.  Chem., L0, 157 (1972),  (92) L . - U . Meyer and A . de Meijere, Tetrahedron L e t t . ,  497 (1976).  - 220 -  (93) (a) D.J. Pasto and C R . Johnson, "Organic Structure Determination", P r e n t i c e - H a l l Inc., Englewood C l i f f s , N.J., 1969, p. 207. (b) J.A. Pople, W.G. Schneider and H.J. Bernstein, "High Resolution Nuclear Magnetic Resonance", McGraw-Hill Inc., 1959, ch. 19 and references t h e r e i n . (94) H. Schenker, J . I . Lauritzen, J r . , R.J. C o r r i c c i n i and S.T. Lonberger "Reference Tables f o r Thermocouples", National Bureau of Standards C i r c u l a r , 561 (1955), U.S. Government P r i n t i n g O f f i c e ,  Washington,  D.C., p. 35. (95) H.V. Euler, H. Hasselquist and A. Glaser, Ark. Kemi, 3, 49 (1951). (96) A. Mandelbaum and M. Cais, J . Org. Chem., 27, 2245 (1962). (97) (a) A.C. Cope, D.S. Smith and R.J. Cotter, Org. Syntheses C o l l . Vol.  4, 377 (1963).  (b) I. Iwai and J . Ide, Org. Syn., 50, 62 (1970). (c) C.F.H. A l l e n , C.G. E l i o t and A. B e l l , Can. J . Res. (B), 17, 87 (1939) (98) (a) L.F. F i e s e r , "Experiments i n Organic Chemistry", 2nd Ed., D.C. Heath and Co., Boston, Mass., 1941, p. 228. (b) L.F. Fieser and F.C. Chang, J . Am. Chem. S o c , 64, 2048 (1942). (99) C.F.H. A l l e n and A. B e l l , Org. Syn., 22, 37 (1942). (100) A.G. Brook, J . Chem. S o c , 5040 (1952). (101) M.F. A n s e l l , B.W. Nash and D.A. Wilson, J . Chem. S o c , 3023 (1963). (102) M.F. A n s e l l , B.W. Nash and D.A. Wilson, J . Chem. S o c , 3027 (1963).  - 221  -  APPENDIX  >—>  A 60 MHz PMR Spectrum o f 5ct,8a-Dimethyl-4a3,5,8,8aBt e t r a h y d r o - 1 , 4 - n a p h t h o q u i n o n e , 1..  F i g u r e 33.  f  '  1  i  F i g u r e 34.  1  1  r — — r  F o u r i e r T r a n s f o r m 100 MHz PMR Spectrum of 5,8,15,18Tetramethylpentacyclo[10.8.0.0 > .0^,9.ol4,19] icosa6,16-dien-3,10,13,20-tetrone, IA. 2  1 1  e  - 222 -  Figure 35.  A 60 MHz PMR Spectrum of 6,7-Dimethyl-4aB,5,8,8agtetrahydro-1,4-naphthoquinone, _2.  *-CDCI  3  impurity (see Figure 55)  7'  Figure 36.  Fourier Transform 100 MHz PMR Spectrum of 6,7,16,17Tetramethylpentacyclo [ 1 0 . 8 . 0 . 0 » . 0 >.0** > ] eicosa6,16-dien-3,10,13,20-tetrone, 2A. 2  11  4  9  1  19  223  Figure 37.  A 60 MHz PMR Spectrum of 4af3,5,8,8a3-Tetrahydro-l,4naphthoquinone, 3_.  *^.CDCL  iimpurity  3  * * — noise spike  see Figure 55/  2A. THS  residual C tJCt,  •  L.  1  Figure 38.  2  0J •H-H-f-  Fourier Transform 100 MHz PMR Spectrum of Pentacyclo[10.8.0.0 » .0 ;» .0 » ]eicosa-6,16-diene-3,10,13,20tetrone, 3A. 2  11  4  9  14  19  - 224 -  F i g u r e 39-  A 60 MHz PMR Spectrum o f 6,7-Diphenyl-4aB,5,8,8agtetrahydro-1,4-naphthoquinone, 4^  F i g u r e 40.  A 100 MHz PMR Spectrum o f l - H y d r o x y - 7 , 8 - d i p h e n y l t r i c y c l o [5.3.0.0 » 0]deca-2,8-dien-4-one, 4A. 5  1  F i g u r e 41.  A 60 MHz PMR Spectrum o f 2,3,6,7-Tetramethyl-4aB,5,8,8a6tetrahydro-1,4-naphthoquinone, 5_.  Figure 43.  A 100 MHz PMR Spectrum of l-Hydroxy-2,3-benzo-7,8dimethyltricyclo[5.3.0.05>10]d _8-ene-4^-one, 6A. eca  - 227 -  Figure 44.  A 60 MHz PMR Spectrum of 4a3,8a3-Dicyano-6,7-dimethyl4a8,5,8, 8ag-tetrahydro-l,4-naphthoquinone, 7_.  Figure 45.  A 100 MHz PMR Spectrum of l-Hydroxy-5,10-dicyano-7,8d i m e t h y l t r i c y c l o [ 5 . 3 . 0 . 0 5 ' 1 0 ] d e c a - 2 , 8 - d i e n - 4 - o n e , 7A.  Figure 47.  A 100 MHz PMR. Spectrum of 5,10-Dicyano-6,9-dimethyl-lloxatetracyclo[6.2.1. 0^» .0^»10]undec-2-ene-4-one, 8A. 7  - 229 -  Figure 48.  A 60 MHz PMR Spectrum of 2,3,4a3,6,7,8aB-Hexamethyl4ag,5,8,8aB-tetrahydro-l,4-naphthoquinone, 9.  Figure 49/  A 100 MHz PMR Spectrum of l-Hydroxy-2,3,5,7,8,10hexamethyltricyclo[5.3.0.0 » ]deca-2,8-dien-4-one, 5  10  9A.  - 230 -  Figure 50.  A 100 MHz PMR Spectrum of 2,3,5,7,8,10-Hexamethylt r i c y c l o [ 6 . 2 . 0 . 0 > ]deca-2-en-6,9-dione, 9B. 5  10  - 231 -  Figure 51.  A 60 MHz PMR Spectrum of 2,3,4ag,5a,8a,8ag-Hexamethyl4af3,5,8, 8ag- tetrahydro-1,4-naphthoquinone, 10.  - 232 -  -Figure 52.  A 60 MHz PMR Spectrum of 2,3,4a3,5g,8r3 ,8aB-Hexamethyl4ag,5,8,8a8-tetrahydro-l,4-naphthoquinone, 11.  - 233 -  Figure 54.  A 100 MHz PMR Spectrum of 1,4,5,7,8,10-Hexamethyltricyclo[6.2.0.0 »- ]deca-2-en-6,9-dione, 11B; (a) 1000 Hz sweep width; (b) 250 Hz sweep width of the 6.5-5.25 6 region with amplitude magnification of x l O ; (c) 250 Hz sweep width of the 3.05 - 0.8 6 region. 5  L0  \  - 234 -  A residual  SAMPLE  CF CDCL  CHCl  TMS *  = impurity  * * =noise spikes  0  Figure 55.  6  5  Fourier Transform 100 MHz PMR Spectrum of CDC1 from Merck Sharp & Dohme Canada Limited, Kirkland, Quebec.  - 235 -  UV Absorption Spectra of Substrates 1-11  A l l the tetrahydro-1,4-naphthoquinones i n this investigation  which have been studied  show two p r i n c i p a l absorptions i n the UV.  The  absorption due to the H,TI* t r a n s i t i o n reminiscent of a,$-unsaturated ketones occurs i n the range 225 - 280' nm and i s the more intense of the two bands.  The absorption at longer wavelength, >_340 nm, i s due  mostly to a forbidden  n,Ti*  t r a n s i t i o n and i t s e x t i n c t i o n c o e f f i c i e n t  for a l l substrates was _<150.  The i n t e n s i t y of this l a t t e r absorption 30  may be enhanced through mixing with the allowed  Tr,Tr*  transition  Absorptions for the i n d i v i d u a l compounds are given i n Table XVI. Table XVI*  UV Absorption Spectra of Substrates JL-11  Compound  Band 1  Band I I A ,nm(e) max  1 (benzene)  371 (68)  2 (MeOH)  226  (8.7xl0 )  3 (benzene)  280  (7.5xl0 )  h_ (MeOH)  280  (7.5x10 )  342 (72)  _5 (MeOH)  225  (9.4xl0 )  330 (115)  6_ (MeOH)  250 296  (l.lxlO ) (1.9xl0 )  340 (150)  7_ (MeOH)  225  (8.9xl0 )  340 (93)  8 (MeOH)  240  (6.2xl0 )  352 (64)  9_ (MeOH)  251  (l.lxlO )  280-400 (e340=146)  3  3  3  ^  370 (63)  4  3  3  3  4  10 (benzene) 11 (MeOH)  370 (70)  3  350 (83) 251  * (Compiled from Reference 24).  (8.7xl0 ) 3  340 (70)  - 236 -  As mentioned i n the text, the i r r a d i a t i o n s of these substrates i n the s o l i d state were c a r r i e d out at the same wavelengths as 24 reported f o r the i r r a d i a t i o n s i n s o l u t i o n  , i . e . , X >^ 340 nm.  This  has allowed f o r a more v a l i d comparison of r e a c t i v i t y differences i n the two phases than would have been p o s s i b l e otherwise.  With 22 regard to e a r l i e r investigations of substrate _3 using sunlight and 23 P y r e x - f i l t e r e d UV l i g h t , respectively, the r e s u l t s presented here would seem to i n d i c a t e a wavelength dependence f o r these reactions. 22 23 Thus, i t i s very l i k e l y that t a r formation as e a r l i e r observed  '  i s promoted by e x c i t a t i o n of a l l the chromophores while a more s e l e c t i v e e x c i t a t i o n (mostly  n,Tr*)  leads cleanly to dimer formation  when intermolecular separation and geometry favor  i t or to  intramolecular processes when the former process i s blocked.  

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