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Conformational effects in the photochemistry of tetrahydro-1,4-naphthoquinones Jennings, Barry Michael 1975

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CONFORMATIONAL  EFFECTS IN THE  PHOTOCHEMISTRY OF TETRAHYDRO-1,4-NAPHTHOQUINONES  by  BARRY MICHAEL JENNINGS B.Sc.  (Hon.). U n i v e r s i t y  o f C a l g a r y , 1970  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE  REQUIREMENTS FOR THE DEGREE OF  : DOCTOR OF PHILOSOPHY  i n t h e Department of CHEMISTRY  We a c c e p t t h i s required  THE  t h e s i s as conforming  to the  standard  UNIVERSITY OF BRITISH COLUMBIA September, 1975  In presenting this thesis  in partial fulfilment of the requirements for  an advanced degree at the University of B r i t i s h Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this  thesis  for scholarly purposes may be granted by the Head of my Department or by his representatives.  It  is understood that copying or publication  of this thesis for financial gain shall not be allowed without my writ ten pe rm i ss i on .  Department of The University of B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5  Date  £W  A ,  l 9 7 £  - ii  -  ABSTRACT The p h o t o c h e m i s t r y  of a v a r i e t y o f  ( s t r u c t u r e 1) has been i n v e s t i g a t e d .  tetrahydro-1,4-naphthoquinones  These were s y n t h e s i z e d by  D i e l s - A l d e r r e a c t i o n of c o r r e s p o n d i n g _p_-quinones  and a c y c l i c - 1 , 3 - d i e n e s .  0  I Three s u b s t i t u e n t - d e p e n d e n t (1) f o r adducts  types of r e a c t i o n s were observed:  p o s s e s s i n g hydrogen s u b s t i t u e n t s a t C^  (bridgehead p o s i t i o n ) , the p r e v a l e n t p r o c e s s was of a 3-hydrogen atom from C  c  j c a r b o n y l oxygen.  (or e q u i v a l e n t l y , C ) o c  at  by  bond f o r m a t i o n (proceeded  by c o n f o r m a t i o n a l r o t a t i o n about  r a d i c a l so produced.  Cg  &  one of a b s t r a c t i o n excited  I n g e n e r a l , t h r e e product types were then  d e r i v e d from carbon-carbon  allylic  and  a  observed,  i n two i n s t a n c e s  the C. - C bond) i n the b i s 4a oa Q  P l a c i n g a methyl  or phenyl s u b s t i t u e n t  renders the 3-hydrogens n o n - e q u i v a l e n t , and a b s t r a c t i o n o c c u r s  i n a c c o r d w i t h e x p e c t a t i o n s based  on the f o r m a t i o n of the more s t a b l e  b i r a d i c a l intermediate. I n adducts p o s s e s s i n g bridgehead the C. - C„ bond i n the b i r a d i c a l 4a 8a p r o d u c t type  substituents, rotation  i s suppressed r  and o n l y a s i n g l e  (enone a l c o h o l ) i s formed, which p o s s e s s e s  r e l a t i v e c o n f o r m a t i o n as the b i r a d i c a l and  about  J  the same  s t a r t i n g adduct.  In the  -  iii  -  case where the b r i d g e h e a d s u b s t i t u e n t s  a r e c a r b o x y m e t h y l , however,  secondary p h o t o l y s i s i n benzene s o l u t i o n o c c u r s , p r o d u c t where the b r i d g e h e a d s u b s t i t u e n t s (2) For the adduct p o s s e s s i n g 5 and Cgj  g i v i n g r i s e to a  are n e a r l y e c l i p s e d .  exo-methyl s u b s t i t u e n t s a t p o s i t i o n s  8 as w e l l as methyls a t the b r i d g e h e a d p o s i t i o n s and  3-hydrogen a b s t r a c t i o n was  at  and  p a r t i a l l y suppressed i n f a v o r o f  a  p r o c e s s t e n t a t i v e l y c o n c l u d e d t o i n v o l v e y~hydrogen a b s t r a c t i o n e x c i t e d enone carbon, g i v i n g r i s e t o a p r o d u c t , the which a g a i n r e q u i r e s l i t t l e c o n f o r m a t i o n a l (3) For adducts p o s s e s s i n g  formation  change i n the  endo-methyl s u b s t i t u e n t s  at C  of  biradical. c  and  C  _)  as w e l l as b r i d g e h e a d s u b s t i t u e n t s , a n o v e l  by  D  o  oxetane p r o d u c t was  observed,  f o r m a l l y the r e s u l t of a c y c l o a d d i t i o n r e a c t i o n i n v o l v i n g the remote double bond and the  one  of the c a r b o n y l  duroquinone adduct was  s t a r t i n g m a t e r i a l and, novel  cage  The  The  oxetane d e r i v e d  from  found to be p h o t o l a b i l e , g i v i n g back  eventually,  a quantitative conversion  to a  diketone.  r e a c t i v i t y d i f f e r e n c e s f o r t h e s e systems, as w e l l as f o r t h o s e  previously studied the  groups.  i n our l a b o r a t o r y , a r e i n t e r p r e t e d as b e i n g  e f f e c t s of s u b s t i t u e n t s on the energy b a r r i e r t o  isomerization  i n the b i r a d i c a l  to  conformational  intermediates.  F i n a l l y , the p o t e n t i a l u t i l i t y of t h e s e p h o t o c h e m i c a l f o r the s y n t h e s i s  due  of u n u s u a l r i n g systems i s noted.  reactions  - iv-  TABLE OF CONTENTS Page INTRODUCTION  \  1  1.  General  1  2.  Photochemistry of Diels-Alder Adducts  7  3.  Objectives of Present Research  31  RESULTS AND DISCUSSION . .. 1.  34  Diels-Alder Adducts of Mono-substituted jcv-Benzoquinones with 2,3-Dimethyl-l,3-butadiene A.  4a3,5,8,8aB-tetrahydro-2,6,7-trimethyl-l,4naphthoquinone  B.  34  (95)  ...  6,7-Dimethyl-2-phenyl-4a,5,8,8a-tetrahydro1,4-naphthoquinone (96)  C. 2.  3.  35  46  Discussion of Photochemistry of 95 and  Diels-Alder Adduct of  ...  53  2,3-Dimethyl-_p_-Benzoquinone  with 2,3-Dimethyl-l,3-butadiene (97)  55  Diels-Alder Adducts with Bridgehead Substituents.  61  A.  4a3,8a3-Dicyano-6,7-dimethyl-4a,5,8,8a-tetra-r hydro-1,4-naphthoquinone  B.  (98)  63  2,3-Dichloro-4a3,8a3-dicyano-6,7-dimethyl4a,5,8,8a-tetrahydro-1,4-naphthoquinone  C.  (99).  68  4a3 8a3-Dicarbomethoxy-6,7-dimethyl-4a,5,8,8a s  -tetrahydro-1,4-naphthoquinone  (100)  71  - V -  Page A.  D i e l s - A l d e r Adducts of Some Substituted j>-Benzoquinones w i t h Hexa-2,4-diene A.  78  D i e l s - A l d e r Adducts of Duroquinone w i t h }  trans,trans-hexa-2,4-diene (101 and 102) a)  79  P h o t o l y s i s of 2,3,4a3,53,S3,8a3hexamethyl-4a,5,8,8a-tetrahydro1,4-naphthoquinone (101)  b)  81  P h o t o l y s i s of 2,3,4a6,5a,8a,8a6hexamethyl-4a,5,8,8a-tetrahydro1,4-naphthoquinone (102) .  B.  4a3,8a3-Dicyano-5a,8a-d imethyl-4a,5,8, 8a-tetrahydro-l,4-naphthoquinone (103).  5.  87  Discussion  96 99  EXPERIMENTAL  140  BIBLIOGRAPHY  181  APPENDIX  192  - vi LIST OF FIGURES Page Figure  1 2 3 4 5  >  „... .. ..  6  7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30  , ..  ; .  5 12 38 39 41 43 48 51 57 59 62 65 66 70 72 73 82 83 84 89 90 94 97 123 122 126 127 128 136 138  - vii LIST OF SCHEMES Page Scheme  1 2 3 4  .'....«,  4 *  6  5  6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41  :  9 10 10 13 16 16 17 19 20 22 23 34 44 45 52 56 60 63 68 68 71 74 75 77 80 86 87 93 96 102 103 105 107 107 I l l 114 117 120 133  - viii LIST OF TABLES Page  Table  I II III IV V VI VII VIII IX X XI XII  29 36 46 62 106 112 113 115 116 119 122 130  - ix -  ACKNOWLEDGEMENT  I w i s h , f i r s t o f a l l , t o thank D r . John R. S c h e f f e r advice,  s u p p o r t , and encouragement d u r i n g  a t U.B.C.  for his  t h e c o u r s e o f my  studies  I t was a p r i v i l e g e and p l e a s u r e t o work f o r a man who  c o u p l e s a p r o f e s s i o n a l a t t i t u d e towards h i s work w i t h a p e r s o n a l i n t e r e s t i n h i s students.  I a l s o w i s h to. thank t h e f a c u l t y and g r a d u a t e s t u d e n t s o f t h e Chemistry Department, and e s p e c i a l l y my co-workers i n , l a b 346, whose f r i e n d s h i p s made my s t a y a t U.B.C. most e n j o y a b l e .  Furthermore, I w i s h to thank my w i f e , typing  Susan, f o r h e r e x c e l l e n t  o f t h i s t h e s i s and f o r h e r p a t i e n c e d u r i n g  its  preparation.  I a l s o express my thanks t o my f a t h e r , E.W. J e n n i n g s , f o r t h e e x c e l l e n t j o b o f mounting t h e many diagrams.  F i n a l l y , I e x p r e s s my g r a t i t u d e  to the U n i v e r s i t y  f i n a n c i a l support i n t h e form o f a T e a c h i n g  o f B.C. f o r  Assistantship.  - 1 -  INTRODUCTION 1.  General Photochemistry, which deals w i t h chemical r e a c t i o n s that are  dependent on the a c t i o n of v i s i b l e or u l t r a v i o l e t l i g h t , has been an area of intense a c t i v i t y i n the past twenty years.  However, p r i o r  to that, the f i e l d received only l i m i t e d a t t e n t i o n , w i t h most s t u d i e s being concerned w i t h gas-phase r e a c t i o n s .  S o l u t i o n photochemistry  was neglected, l a r g e l y because the techniques now a v a i l a b l e to r e s o l v e the complex mixtures of products o f t e n encountered had not yet been developed.  As w e l l , i n v e s t i g a t o r s were handicapped by the u n a v a i l a b i l i t y  of adequate a r t i f i c i a l sources of l i g h t .  As one author noted,  "... w i t h the sun as the c h i e f source of r a d i a t i o n , progress i n the f i e l d o f t e n depended on the weather!"  1  This s i t u a t i o n s t a r t e d to change d r a m a t i c a l l y i n the l a t e 1950's, when i t was r e a l i z e d that photochemistry offered p o t e n t i a l access to unusual, and t h e r e f o r e i n t e r e s t i n g , r i n g systems which would be very d i f f i c u l t , i f not i m p o s s i b l e , to synthesize by other methods.  Isomerization of the norbornadiene d e r i v a t i v e  to the corresponding  quadricyclene 1_ (eq. I ) and photoconversion of carvone 3_ to carvone2  camphor 4^ (eq. 2 ) were two of the e a r l i e s t examples of j u s t t h i s 3  point.  A short time l a t e r , Eaton and Cole published * t h e i r c l a s s i c a l 1  synthesis of cubane 1_ i n which the key intermediate J> was obtained  hv  (eq. 1)  hv  (eq. 2)  by p h o t o l y s i s of the r e a d i l y a v a i l a b l e cyclopentadienone dimer _5 (eq. 3). I t was not long u n t i l the photochemical method became accepted as a key t o o l i n the synthesis of h i g h l y s t r a i n e d p o l y c y c l i c  Br  Br  hv • Br  few steps  \J  (eq. 3)  - 3 r i n g systems?  J u s t as q u i c k l y , i n v e s t i g a t o r s began to e x p l o r e  the  n a t u r e of the a c t u a l p h o t o c h e m i c a l p r o c e s s e s t h e m s e l v e s , to the t h a t , a t the p r e s e n t t i m e , the  f i e l d has  i n t o one  o f wide and  f a c t are  the thousands of r e s e a r c h  all  expanded tremendously  v a r i e d areas of research.  Testimony to t h i s  papers p u b l i s h e d  i m p o r t a n t f a c t o r w h i c h may  from which the r e a c t i o n o r i g i n a t e s . possible spin configurations they were i n the  produced.  On  may  On  result.  I f a l l s p i n s remain  state i s obtained.  process;  triplet  the e x c i t e d hence the  triplet  excited  state.  than the e x c i t e d  a  state i s a  population  of  excited intermolecular intersystem  Likewise, deactivation  s t a t e to the ground s t a t e s i n g l e t i s  triplet  paired,  Direct excitation  ( c a l l e d s e n s i t i z a t i o n ) or i n t r a m o l e c u l a r  c r o s s i n g from the s i n g l e t e x c i t e d  two  state i s  s t a t e s must o c c u r v i a a secondary p r o c e s s , e i t h e r  energy t r a n s f e r  state.  state  the o t h e r hand, i f e x c i t a t i o n i s accompanied by  quantum m e c h a n i c a l l y f o r b i d d e n  majority  a  electronic excitation,  from a ground s t a t e s i n g l e t to an e x c i t e d  lived  excited  ground s t a t e , then a s i n g l e t e x c i t e d  spin inversion process, a t r i p l e t  triplet  on  synthetic.  a f f e c t the outcome of  p h o t o c h e m i c a l r e a c t i o n i s the m u l t i p l i c i t y of the  as  annually  a s p e c t s o f p h o t o c h e m i s t r y , m e c h a n i s t i c as w e l l as  One  point  forbidden;  s t a t e of a m o l e c u l e i s s u b s t a n t i a l l y  s i n g l e t s t a t e , and  f o r t h i s reason  of observed p h o t o c h e m i c a l r e a c t i o n s  longer-  the  o c c u r from the  However, a number o f s i n g l e t s t a t e r e a c t i o n s  from  triplet  are known,  - 4 -  and these may or may not g i v e r i s e to products d i f f e r e n t from those o r i g i n a t i n g from a t r i p l e t s t a t e .  An example i n which s i n g l e t s and  t r i p l e t s lead to d i f f e r e n t products i s found i n the photochemistry of 3 , Y ~  u n s a t  urated  ketones, represented i n Scheme l .  6  SCHEME 1  0  0  The s i n g l e t s t a t e gives a product a r i s i n g from a 1,3-acyl m i g r a t i o n , w h i l e the t r i p l e t s t a t e leads to cyclopropane r i n g formation.  By f a r the most f r e q u e n t l y encountered chromophore (or part of the molecule which absorbs l i g h t ) i s the carbonyl group.  The u l t r a v i o l e t  spectrum of a simple a l i p h a t i c ketone features two d i s t i n c t absorptions. The f i r s t , and more intense, band a r i s e s out of e x c i t a t i o n of an e l e c t r o n from the carbonyl TT o r b i t a l to i t s antibonding TT * and i s termed a TT - TT t r a n s i t i o n .  orbital,  I t i s u s u a l l y found i n the r e g i o n  from 200  - 250  coefficient.  nm The  and  has  a high  (1,000 - 100,000) e x t i n c t i o n  second a b s o r p t i o n  band i s due  to the  e x c i t a t i o n of  an  e l e c t r o n from the non-bonding JD o r b i t a l on oxygen to the  IT  orbital.  from 270  C a l l e d the n - IT  - 400  nm,  transition, i t i s generally  depending on  i n the m o l e c u l e , and  has  a low  intersystem  singlet excited  crossing  to the  found  the degree o f c o n j u g a t i o n p r e s e n t e x t i n c t i o n c o e f f i c i e n t (10 -  because i t - i s a space f o r b i d d e n of the n - IT  carbonyl  transition.  One  100)  important  feature  s t a t e i s i t s h i g h e f f i c i e n c y of  triplet  excited  state.  This  -5 state possesses a r e l a t i v e l y long  l i f e t i m e (10  latter  -3 - 10  sec)  - 9 - 5 compared to t h a t of the  singlet state  from which i t o r i g i n a t e d .  (10  -  A g a i n , t h i s i s due  m e c h a n i c a l ) f o r b i d d e n e s s of the T^ **- S  q  10  sec)  t o the  process.  spin  Figure  (quantum l  7  gives  * a three-dimensional representation  of the n - IT  «5>  *  1.  An  # 3 b  fa  Figure  transition.  *  A r e p r e s e n t a t i o n of the n - TT t r a n s i t i o n , •.IT system electrons; o, e l e c t r o n s i n an sp o r b i t a l c o - a x i a l to C-0 bond; y, e l e c t r o n s i n the p o r b i t a l of oxygen; =.'•:-.= TT bond e l e c t r o n s ; anti^bonding o r b i t a l s .  the  F  «  * electron  i n the non-bonding £ ^  o r b i t a l i s excited  t o the TT  orbital,  l e a v i n g b e h i n d an o r b i t a l on oxygen which i s e l e c t r o n d e f i c i e n t .  - 6 -  A behavioral s i m i l a r i t y to an alkoxy r a d i c a l may thus be expected, 8  and i s i n fact observed;  *  the n - TT excited state, l i k e the alkoxy  r a d i c a l , i s a powerful hydrogen atom abstracting species. A frequently encountered photochemical reaction of ketones arising from the n - TT excited state i s the Norrish I I reaction, depicted i n Scheme 2.  I n i t i a l n - TT excitation i s followed by  hydrogen atom abstraction through a six-membered t r a n s i t i o n state SCHEME 2.  to give a b i r a d i c a l , which may then suffer bond closure to give a cyclobutanol or f i s s i o n to give a ketone and o l e f i n .  - 7 -  2.  P h o t o c h e m i s t r y of D i e l s - A l d e r I n 1964,  Adducts.  Cookson and co-workers  reported °the 1  r e s u l t s of a  study o f the p h o t o c h e m i s t r y o f some D i e l s - A l d e r adducts o f The adduct w i t h c y c l o p e n t a d i e n e j5 (n = 1) was its  found to i s o m e r i z e to  c o r r e s p o n d i n g cage, compound 9_ (n = 1) i n h i g h y i e l d  8  Similarly  (n=0,l,2)  9  p-benzoquinone.  (eq. 4 ) .  (n=0,l,2)  the adduct w i t h c y c l o h e x a - 1 , 3 - d i e n e j$ ( n = 2 ) , and  as  r e p o r t e d l a t e r J t h e adduct w i t h c y c l o b u t a d i e n e _8 (n = 0 ) , formed x  the  c o r r e s p o n d i n g cage compounds 9_ (n = 2 and 0 r e s p e c t i v e l y ) on irradiation.  S u p r i s i n g l y , the s u c c e s s o f t h i s r e a c t i o n depended  on the p r e s e n c e o f a b r i d g e o r bond j o i n i n g the 1,3-butadiene-benzoquinone  adduct 10 was  c a r b o n atoms 5 and  8;  reported to y i e l d  tar  and i l l - d e f i n e d p r o d u c t s o f t e n t a t i v e s t r u c t u r e _11_, p o s t u l a t e d  to  a r i s e from i n t e r m o l e c u l a r a , 3 - u n s a t u r a t e d double bond d i m e r i z a t i o n .  (eq. 5)  - 8 -  In 1971,  Scheffer and c o - w o r k e r s R e i n v e s t i g a t e d the photochemistry 1  of 10_ and found t h a t , on s e l e c t i v e n - TT e x c i t a t i o n , i n a d d i t i o n to extensive polymer formation, two novel t r i c y c l i c products _12_ and 13 were formed i n 10%  o v e r a l l y i e l d (eq. 6).  The s t r u c t u r e of 12  was  (eq.  6)  Product Ratios i n : Benzene tert-Butanol  unequivocally  1  7  5  1  determined by X-ray a n a l y s i s \ "*while s t r u c t u r e 13  was  assigned on the basis of i t s s p e c t r a l data and q u a n t i t a t i v e thermal conversion  to 12.  The suggested mechanism f o r the r e a c t i o n i s shown i n Scheme 3. * I n i t i a l n - ir e x c i t a t i o n of _10_, followed by 8-hydrogen a b s t r a c t i o n through a five-membered t r a n s i t i o n s t a t e gave the resonance s t a b i l i z e d b i r a d i c a l _1A,  which then underwent bond formation to the enol form3  of 12 and J_3 (15 and Ij5, r e s p e c t i v e l y ) . that adducts  This mechanism also implied  f a i l e d to undergo t h i s r e a c t i o n due to the bridgehead  SCHEME  3.  n a t u r e of the b i r a d i c a l s p e c i e s which would abstraction  result  from the 8-hydrogen  process.  The analogous 2 , 3 - d i m e t h y l - l , 3-butadiene-jJ-benzoquinone _17 was 18-20 18  also studiedl i n vastly  5  P h o t o l y s i s of J_7_ a f f o r d e d t h r e e  products  improved y i e l d s , as shown i n Scheme 4.  and _19_ were analogous to J_2_ and _13_,  adduct  Ene-diones  r e s p e c t i v e l y , w h i l e enone  a l c o h o l 20_ r e p r e s e n t e d a n o v e l s t r u c t u r e .  These r e s u l t s  provided  - 10 -  SCHEME 4.  Isolated Yields i n : Benzene tert-Butanol  trace  35%  22%  80%  trace  trace  a d d i t i o n a l e v i d e n c e f o r t h e mechanism 3-hydrogen a b s t r a c t i o n by c a r b o n y l 21 (Scheme 5 ) , which c o u l d SCHEME 5.  postulated  i n Scheme 3;  oxygen would g i v e r i s e t o b i r a d i c a l  then form bonds between v a r i o u s  ends o f  - l i -  the b l s - a l l y l i c  system to g i v e  22  i n t e r m e d i a c y of enol _22_ (and  and  23.  The  supported by 0-d  the o b s e r v a t i o n  gave isomer _1J3 w i t h one  exo-4 p o s i t i o n  (92%  2XJ d i r e c t l y , and  the  forms  hence of JJ3)  that p h o t o l y s i s  of _17_ i n  deuterium s u b s t i t u t e d  incorporation  enol  was  tert-butanol-  exclusively i n  from mass spectrum) (eq.  7).  the The  (eq.  18  same p r o d u c t was  o b t a i n e d by m i l d base c a t a l y z e d  of p r o t i o ketone 1_8. has  precedent  deuterium exchange  T h i s p r e f e r e n t i a l exchange of the  i n the work of T i d w e l l a n d 1 6  o f some b i c y c l o (2.2.1] heptanones, the r a t e i n compound 25_ over t h a t  i n 2_4  Werstiuk*  7  In a study  enhancement of the  (Figure  c o n t r i b u t i o n of the homoenolate s p e c i e s  26\  2) was 7 a  exo-proton  exchange  a t t r i b u t e d to  the  7)  - 12 -  Relative Rates of Exchange  I —H  24  5.89 x 10 2  2.0  r  exo  -2 4.6 x 10  -5  9.07 x 10'  ^endo  17b  Ref.  R e l a t i v e hydrogen exchange r a t e s i n some b i c y c l o [ 2 . 2 . l] heptanones.  F i g u r e 2.  While 22,  17a  i t was  t h i s e v i d e n c e was  c o m p e l l i n g f o r t h e i n t e r m e d i a c y of e n o l  not f o r e n o l 23, due  to the low y i e l d o f 19_ i n t e r t - b u t a n o l .  To v e r i f y the i n t e r m e d i a c y of 23, a study o f the t e t r a d e u t e r a t e d adduct  2_7 was  undertaken.  P h o t o l y s i s i n anhydrous benzene (eq.  y i e l d e d the c o r r e s p o n d i n g t e t r a d e u t e r a t e d ene-dione  D  D  28_, analogous  0  hv  (eq. 8)  Mass s p e c t r o s c o p y showed a l o s s of o n l y 8.4% corresponded (nmr  8)  to a 66% deuterium  spectrum),  deuterium,  i n c o r p o r a t i o n a t the  assuming t h a t no l o s s o f d e u t e r i u m had  which position occurred  to  19.  - 13 at other p o s i t i o n s .  T h i s s t r o n g l y supported  the i n t e r m e d i a c y  of  e n o l 2 3 _ (and a l s o 1 6 ) .  The  photoproducts  of thermal  and  1 8 - 2 0 were found  photochemical  t o be  i n t e r r e l a t e d by a s e r i e s  r e a r r a n g e m e n t s , shown i n Scheme 6 ,  w h i c h a l s o s e r v e d to c o r r o b o r a t e t h e i r s t r u c t u r e s .  The  thermal  SCHEME 6 .  benzene c o n v e r s i o n o f _19_  ( l i k e t h a t of 13^  1 2 ) constituted a [ l , 3 ]  s u p r a f a c i a l s i g m a t r o p i c rearrangement, f o r m a l l y f o r b i d d e n by WoodwardHoffmann r u l e s a n d t h e r e f o r e was 1 8  hand, the p h o t o c o n v e r s i o n  of 2 0 ^  l i k e l y non-concerted 1S_ and  of 2 0 -*• 1 8 were examples of a l l o w e d rearrangements r e s p e c t i v e l y . uncertain;  [l,3J  and  Whether they  19  On the  conversion  [ 3 , 3 ] sigmatropic  (eq. 9 ) .  f o r m a t i o n o f equal amounts of ^ 0 and _31 was i n t e r p r e t e d  i n terms o f the b i r a d i c a l i n t e r m e d i a t e 32_ w h i c h underwent formationl  9 a  was  19_ t r a n s f o r m a t i o n  to be n o n - s t e r e o s p e c i f i c , i e . n o n - c o n c e r t e d  bond r o t a t i o n p r i o r to p r o d u c t  other  were i n f a c t c o n c e r t e d  a r e a c t i o n analogous t o the 2 ! 0  had been s h o w n The  the t h e r m a l  2 0  The  photochemical  - 14 -  hv  +  29 (eq.  9)  32  t r a n s f o r m a t i o n o f /20 -»- _18, f o r m a l l y a rearrangement,  [3,3] s u p r a f a c i a l s i g m a t r o p i c  i s a l s o n o t a l l o w e d by t h e Woodward-Hoffmann  S c h a f f n e r and c o - w o r k e r s h a v e observed 21  a s i m i l a r type  rulesl ' 8  2 0  rearrangement  i n t h e p h o t o l y s i s o f _33 (eq. 10).  hv [3,3] 33  (eq.  10)  0  The o r i g i n o f t h e d r a m a t i c s o l v e n t e f f e c t on t h e p r o d u c t d i s t r i b u t i o n i n b o t h adducts possibility  H) and _17 was n o t a t a l l c l e a r .  t h a t _18 and 1_9_ were secondary  out by time-dependence s t u d i e s .  p r o d u c t s o f 20.  w  a  s  The ruled  One s u g g e s t i o n i n v o k e d t h e f o r m a t i o n 1 5  of the z w i t t e r i o n i c  2 2  intermediate  35_, s t a b i l i z e d i n  tert-butanol  by hydrogen bonding and s o l v a t i o n of the p o s i t i v e charge a t Preferential  3,8 b o n d i n g , w i t h subsequent  expected to o c c u r as was o b s e r v e d . c o u l d be i n t e r p r e t e d  at  In b e n z e n e ,  therefore,  so formed (19 and 20) are  position.  However, the  thermodynamically u n s t a b l e ,  t h a t i n benzene,  c o n t r o l l e d due to the p o s s i b l y c l o s e r  products  exemplified  G a y l e r advanced 2 3  the p h o t o l y s i s i s k i n e t i c a l l y  resemblance  s t r u c t u r e of the i n t e r m e d i a t e  b i r a d i c a l 2_1;  would have a lower a c t i v a t i o n  energy  of _19 and 20. to the  and thus t h e i r  (p_-benzoquinone w i t h i s o p r e n e )  formation  (Hammond p r i n c i p l e **). 2  I n an e x t e n s i o n o f t h i s work, the u n s y m m e t r i c a l adduct  regioselectivity  reaction  a b i r a d i c a l or  t h e r m a l c o n v e r s i o n to _18 ( a l s o 13 ->• 12).  the a l t e r n a t e s u g g e s t i o n  the  f o l l o w e d by p r e f e r e n t i a l bond f o r m a t i o n  the i n d u c t i v e l y s t a b i l i z e d  by t h e i r  f o r m a t i o n of JL8, would be  as p r o c e e d i n g through e i t h e r  zwitterionic intermediate,  Cg.  was i n v e s t i g a t e d  of the B-hydrogen a b s t r a c t i o n  2 3  '  2  5  to  process.  of the i n f l u e n c e of a methyl group on a l l y l r a d i c a l  36  determine the Consideration  stability  suggested t h a t the f o r m a t i o n would be f a v o r e d  o f b i r a d i c a l 37. (Scheme 7, p a t h a)  over 38 (path b ) .  Since  an a l l y l r a d i c a l ' s  SCHEME 7.  occupied  highest  OH  m o l e c u l a r o r b i t a l has a node a t t h e c e n t r a l carbon atom, a  methyl s u b s t i t u e n t  t h e r e , as i n 38, would have l i t t l e  whereas a m e t h y l s u b s t i t u e n t on a t e r m i n a l  effect,  c a r b o n , as i n _37 would be  expected t o have a pronounced i n f l u e n c e on t h e s t a b i l i t y o f t h e radical.  T h i s was found t o be t h e c a s e .  P h o t o l y s i s o f 36_ i n e i t h e r  benzene o r t e r t - b u t a n o l gave t h e p r o d u c t s shown i n Scheme 8, i n t h e SCHEME 8.  R e l a t i v e Ratios i n : Benzene  5  3  2  tert-Butanol  -  7  1  - 17 indicated r e l a t i v e r a t i o s .  I n both solvent systems s t u d i e d , the  products r e s u l t i n g from a b s t r a c t i o n at the 8 - p o s i t i o n ( i e . 3[9_ and  40)  predominated over 4_1_, the product of 8'-abstraction.  Related to the s t a b i l i z i n g e f f e c t of a methyl s u b s t i t u e n t was the photochemistry of the p-benzoquinone-trans,trans-2,4-hexadiene adduct 4_2.-  8-Hydrogen a b s t r a c t i o n from e i t h e r carbon atom 5 or 8  would again y i e l d a b i r a d i c a l w i t h a methyl s u b s t i t u e n t at the terminal end of one of the a l l y l systems, such as 43 (Scheme 9)* which would s t a b i l i z e the species.  This was not observed, however.  SCHEME 9.  P h o t o l y s i s i n benzene or t e r t - b u t a n o l l e d to a s i n g l e photoproduct, assigned s t r u c t u r e 4_4 on the b a s i s of spectroscopic data and deuterium  -  exchange s t u d i e s .  The  -  18  mechanism f o r f o r m a t i o n  y-hydrogen a b s t r a c t i o n from the C  45,  or C  C  5  0  o  of 4_4  involved  m e t h y l group to g i v e  which then underwent bonding to g i v e e n o l 4_6_ (the  of which was  intermediacy  a g a i n v e r i f i e d by p h o t o l y s i s i n t e r t - b u t a n o l - O - d )  subsequent k e t o n i z a t i o n i n adduct 4 2 and  to 4 4 .  The  at C ^ Q i n 4 4 was  the mechanism of f o r m a t i o n give structure 4 4 .  stereochemistry  assumed, based on  o f 4_4_;  the e p i m e r i c  a t C , . and  form 4 7 c o u l d  Cg and  not  investigated  to which Y~hydrogen a b s t r a c t i o n c o u l d  w i t h g-hydrogen a b s t r a c t i o n .  and  the s p e c t r a  In a p a r a l l e l s t u d y , adduct 4_8 was  to determine the extent  butanol  biradical  P h o t o l y s i s o f 4_8 i n benzene or  gave p r o d u c t s 4_9_ and _50 i n a r e l a t i v e r a t i o of 7 : 1  compete tert11).  (eq.  (eq.  Thus, d e s p i t e  the f a c t  electronically,  that B-abstraction  the p r o d u c t a r i s i n g  have been  favored  from the s t a t i s t i c a l l y  favored  p r o c e s s of y~hydrogen a b s t r a c t i o n was  I t was o b s e r v e d any  interesting  formed  preferentially.  to n o t e t h a t i n n e i t h e r 4_2_ nor  product r e s u l t i n g  ( a l l y l i c ) hydrogen.  should  T h i s was  4J3 was  there  from a b s t r a c t i o n of the t e r t i a r y a l s o the case i n the p h o t o l y s i s  of  B-  11)  -  19  -  adduct 5l_, i n which the 8-hydrogens are t e r t i a r y , a l l y l i c and benzylic, and therefore i n theory r e a d i l y a b s t r a c t a b l e f  5  I r r a d i a t i o n of 5l_ under  a v a r i e t y of conditions l e d to no detectable change. PK  A possible reason  0 hv  ^  3>  N.R.  for these observations was advanced, based on conformational  analysis.  The butadiene-/p_-benzoquinone r i n g system was d e s c r i b e d i n terms o f 25  f i v e more or less well defined conformeirs A-E, as shown i n Scheme 1 0 . SCHEME 10.  - 20 9  A l s o shown a r e " a c c e s s i b l e " $-hydrogen  t o oxygen d i s t a n c e s  g r e a t e r than 3.5 8 were not c o n s i d e r e d ) . 42) or Ph  7  r (those  When X = H, and Y = CH^  (as i n  (as i n 5 1 ) , o n l y i n conformers A and B a r e t h e B-hydrogens however, t h e s e c o n f o r m a t i o n s a r e d e s t a b i l i z e d by Y -  accessible; ( i e . Me - Me,  Y  4_2_, o r Ph - Ph, 51) non-bonded i n t e r a c t i o n of a b o w s p r i t -  flagpole-like nature  2 8  As w e l l , B-hydrogen a b s t r a c t i o n i n e i t h e r conformer •  A o r B would b r e a k a C-H bond n e a r l y o r t h o g o n a l t o the double bond j> orbitals, i t was  thereby minimizing i n c i p i e n t a l l y l  reasoned ' y-hydrogen 2 3  2 5  radical stability.  Thus,  a b s t r a c t i o n from m e t h y l o c c u r r e d , p o s s i b l y  from conformer C, where t h e m e t h y l hydrogens  can be as c l o s e as 0 . 9  X  from o x y g e n a l t h o u g h conformers D and E a l s o p o s s e s s methyls w i t h 2 3  f a v o r a b l e hydrogen-to-oxygen Finally,  distances  (1.4  A*)  25  to determine t h e e f f e c t s o f m e t h y l s u b s t i t u e n t s a t o t h e r  p o s i t i o n s i n t h e b a s i c r i n g system  ( c f . , compound 10),  duroquinone w i t h 2 , 3 - d i m e t h y l - l , 3 - b u t a d i e n e j>2_ was Photolysis  t h e adduct o f  studied  2 3  '  2 5  i n a v a r i e t y of s o l v e n t s l e d t o p r o d u c t s 53_ - 55 i n the  r e l a t i v e amounts shown i n Scheme 11.  Benzene tert-Butanol Acetonitrile Methanol 1:1 Dioxane - Water  0.5 1.1 4 13 30  E n e - d i o n e 54 r e p r e s e n t s a p r e v i o u s l y  1 1 1 1 1  2 6  -  unobserved product  -  21  s t r u c t u r e , whose s t r u c t u r e was  s p e c t r a l p r o p e r t i e s and as shown i n e q u a t i o n  from i t s two  12.  The  deduced from i t s  s t e p c o n v e r s i o n back to adduct 5J£  thermal  t r a n s f o r m a t i o n _54 -*• _56  represents  (eq.  12)  0  a n o v e l example of a r e t r o - e n e r e a c t i o n ( a r r o w s ) , a l t h o u g h 2 9  c o n c e r t e d mechanism i s a l s o p o s s i b l e . 54 a l s o suggested  the p o s s i b i l i t y  s t r u c t u r e as w e l l ; 53 and 20  found  _18 t r a n s f o r m a t i o n  two  p r e s e n c e of the new  t h a t _53 may  T h i s p r o d u c t was  a novel  thus analogous to compound  to t h e r m a l l y c o n v e r t (Scheme 6 ) .  The  p o s s i b l e mechanisms were c o n s i d e r e d i n v o l v e s an i n i t i a l  to _55, analogous to  s t r u c t u r e of _55 was to compound  e x p l a i n the d i v e r g e n t p h o t o c h e m i c a l  (path A)  have had  behavior  (Scheme 1 2 )  '  8-hydrogen a b s t r a c t i o n by  55) , f o l l o w e d by a p r o t o t r o p i c s h i f t  between carbon atoms 2 and  8 and  a l t e r n a t i v e mechanism (path B)  3 1  the  assigned  of adduct 2 3  20,  18.  2 5  The  52  first  carbonyl  oxygen to g i v e b i r a d i c a l 57_ (which v e r y l i k e l y e x p l a i n s the of j>3 and  structure  3  on the b a s i s of i t s s p e c t r a l s i m i l a r i t i e s  To  less  however, x - r a y a n a l y s i s " s u p p o r t e d t h e s t r u c t u r e  g i v e n i n Scheme 11. as such, was  The  a  to g i v e _58.  k e t o n i z a t i o n then g i v e s 54.  formation Bonding The  c a l l s f o r an i n i t i a l y-hydrogen a b s t r a c t i o n  - 22 SCHEME 12. 0  OH  54 by enone carbon atom 3, g i v i n g b i r a d i c a l ^ 0 , which gives 54 d i r e c t l y upon bond  formation.  The two pathways to photoproduct 5 4 are t h e o r e t i c a l l y d i s t i n g u i s h a b l e since path A requires the intermediate tert-butanol-0-d  enol 5 9 . P h o t o l y s i s of j>2_ i n  or dioxane-D20 ( 1 : 1 ) ' y i e l d e d isomer 5 4 i n which 2 3  there was no deuterium i n c o r p o r a t i o n ; i n the l a t t e r >instance contained  2 5  however, product J55_ i s o l a t e d  e x a c t l y one deuterium atom i n the C  L  - 23 position out  (mass spectrum, nmr).  Thus path A was  i n f a v o r o f B f o r the f o r m a t i o n  of  P r i o r to t h e s e i n v e s t i g a t i o n s by  54.  Scheffer.  examples of 8-hydrogen a b s t r a c t i o n had t h e s e r e s u l t s were known, A g o s t a and  tentatively ruled  et a l , v i r t u a l l y  been r e p o r t e d ?  2  no  Shortly a f t e r  co-workers p u b l i s h e d  a report  i n which a- s e r i e s of a-methylene ketones formed p r o d u c t s r e s u l t i n g from B-hydrogen a b s t r a c t i o n (63 and more f a m i l i a r y h y d r o g e n a b s t r a c t i o n  66)  as w e l l as those from  (Norrish II) process  These r e s u l t s a r e summarized i n Scheme 13. SCHEME  The  formation  (62 and of  13.  61  67  63  62  68  V 69  the  63  65),  - 24 -  and 66_ was a t t r i b u t e d to the intermediacy of a b i r a d i c a l such as 68 ( a r i s i n g from the B-hydrogen a b s t r a c t i o n process), which i s formally a d e r i v a t i v e of trimethylene methane (69), a ground s t a t e t r i p l e t species w i t h a t h e o r e t i c a l l y estimated **delocalization energy 3  of 34 k c a l . mole. photoreactions  1  I t i s i n t e r e s t i n g here to note that the observed  of adducts 10 and JL7_ also r e q u i r e a capacity f o r  extensive s t a b i l i z a t i o n of t h e i r b i r a d i c a l intermediates respectively.  and 21  Compound 7_0, l a c k i n g the ene-dione double bond present  i n _17_, underwent no detectable r e a c t i o n , even a f t e r prolonged periods of i r r a d i a t i o n  3 5  The process of y-hydrogen a b s t r a c t i o n by enone carbon, on the 3 £  other hand, has ample l i t e r a t u r e precedent.  Herz and Nair  reported  one of the e a r l i e s t examples (eq. 13) i n which the proposed r e a c t i v e  s t a t e was the TT - TT , rather than the n - u , based on the phosphorescence spectrum of 7_1.  E l e c t r o n r i c h s u b s t i t u e n t s such as methoxyl are known  37  - 25 * to lower t h e energy o f the TT - TT  triplet  s t a t e , r e l a t i v e to that of  *  *  the n — TT t r i p l e t s t a t e . I n the c a s e o f the t r i p l e t w i t h the lower energy.  the TT — TT  state  was  * As has been mentioned  previously,  t h e n - TT  a p o w e r f u l hydrogen atom a b s t r a c t i n g s p e c i e s ,  excited state i s  and a b s t r a c t i o n by the  oxygen o f a c a r b o n y l group, e s p e c i a l l y from the a - p o s i t i o n o f p r o t i c solvents  ( i e . isopropanol),  i s u s u a l l y a t t r i b u t e d to t h i s  C o n v e r s e l y , the l a c k of such a b s t r a c t i o n state reactions unreactive  (photoreduction) i n t r i p l e t  i s u s u a l l y t a k e n as a s t r o n g  triplet  TT - TT  state.  state.  i n d i c a t i o n o f an  S c h a f f n e r and co-workers  suggested t h a t hydrogen a b s t r a c t i o n by t h e (3-carbon o f an u n s a t u r a t e d ketone i s t y p i c a l o f TT — TT  have a,3-  triplets.  A n o t h e r example o f hydrogen a b s t r a c t i o n by enone carbon p r o v i d e d by N a k a n i s h i and c o - w o r k e r s ? d i a c e t a t e _7_3 i n a v a r i e t y o f s o l v e n t s c y c l i z e d p r o d u c t _74 (eq. 14).  H  9  Photolysis y i e l d e d the  In t h i s instance,  of  was  taxinine  transannularly the a b s t r a c t i o n  H  - 26 was  by the a-carbon  indicated yield  atom;  s e n s i t i z a t i o n and  a reactive triplet  state.  quenching  experiments  In a d d i t i o n , the h i g h quantum  i n p o l a r s o l v e n t s (0.091 i n dioxane; 0.078 i n t e r t - b u t a n o l )  r e l a t i v e to t h a t i n benzene (0.031) l e d the a u t h o r s to conclude the r e a c t i v e t r i p l e t was t h i s c o n c l u s i o n was isopropanol resulted  a TT -  i n no hydrogen  number of a,8-unsaturated  a r o s e v i a a hydrogen  state.  A d d i t i o n a l evidence f o r  the o b s e r v a t i o n t h a t p h o t o l y s i s of 7_3 i n  A g o s t a and c o - w o r k e r s '  e q u a t i o n s 15 - 17.  TT  I t was  +0-1  * have 2  a b s t r a c t i o n from  s t u d i e d the p h o t o c h e m i s t r y of a  cj'clopentenone systems,  r e p r e s e n t e d by  p o s t u l a t e d i n each case t h a t the p r o d u c t s  a b s t r a c t i o n to g i v e o l e f i n s , or  between the ends o f the b i r a d i c a l i n t e r m e d i a t e s . e q u a t i o n s 16 and  solvent.  a b s t r a c t i o n by the 6-carbon atom, f o l l o w e d by  e i t h e r secondary hydrogen  to  17, i t was  bonding  With r e f e r e n c e  noted t h a t the c a r b o n y l moiety  not be a p a r t o f the c y c l o p e n t e n e r i n g .  to o r i g i n a t e from a t r i p l e t  excited  f o r the involvement o f a rr - Tf  they were  state? ' 3  R e t u r n i n g t o the case o f compound 5J2, t h e r e was precedent  need  As these r e a c t i o n s c o u l d  be s e n s i t i z e d and quenched w i t h no change i n p r o d u c t r a t i o s , thought  triplet  a l s o some  state.  Depending  on the degree o f s u b s t i t u t i o n , a s t r i k i n g d i f f e r e n c e i n p r o d u c t s observed  that  i n the p h o t o r e a c t i o n of a v a r i e t y of jo-benzoquinones  was  with  - 2 7  olefins.  -  With no substituent present ( i e . £-benzoquinone, 75) the  sole product formed"*"*was the oxetane 76 (eq. 18), the r e s u l t of a 2+2  cycloaddition of o l e f i n to the carbonyl group.  I i  With methyl  - 28 -  0  +  hv  (eq. 0  O 77  78  79  substituents present, i n a d d i t i o n to oxetane formation, the process of  2+2  19)  competitive  c y c l o a d d i t i o n of o l e f i n to the ene-dione double,  bond was observed, y i e l d i n g cyclobutanes, as i n the case of 77 (eq. 19)'j In c e r t a i n instances, e x c l u s i v e cyclobutane formation was These r e s u l t s are summarized i n Table i l *  observed.  6  I t was t e n t a t i v e l y c o n c l u d e d t h a t the d i f f e r e n t products h7  were formed from d i f f e r e n t excited s t a t e s : and 77 — TT leading to cyclobutanes.  * n - TT g i v i n g oxetanes  However, a study by Pappas and  Portnoy * suggested that t h i s may not be the case. 1  8  naphthoquinone  Using  1,4-  as a model, no dependence of the product r a t i o on  solvent was observed which argued against the p a r t i c i p a t i o n of d i f f e r e n t excited states.  In the case of compounds JK) and j H , i t had been  suggested that e x c l u s i v e cyclobutane formation o r i g i n a t e d from a TT — TT  e x c i t e d s t a t e , lowered i n energy by the e l e c t r o n r e l e a s i n g  e f f e c t of the methoxyl s u b s t i t u e n t ?  7  However, Portnoy and Pappas * 1  8  showed that 6-methoxy?-l,4-naphthoquinone (85), which they reasoned should a l s o show an enhanced r a t i o of cyclobutane formation due to the a b i l i t y of the methoxyl group to s t a b i l i z e a TT - TT  triplet  at p o s i t i o n 2, y i e l d e d v i r t u a l l y the same product r a t i o as the  - 29 TABLE I. A.  PHOTOREACTIVITY OF _p_-QUINONES WITH OLEFINS.  Exclusive Oxetane Formation. 0  B.  Concurrent Oxetane and Cyclobutane Formation. 0  C.  0  Exclusive Cyclobutane Formation.  87  88  89  0  D.  0  No Addition. 0  90  - 30 unsubstituted analog 83.  These r e s u l t s were i n t e r p r e t e d as i n d i c a t i n g  that the presence of the methoxyl was important only when i t was s i t u a t e d on the double bond p a r t i c i p a t i n g i n the r e a c t i o n .  Furthermore,  i t was concluded * that the e f f e c t s of the methoxyl (or methyl) group 1  were, a)  8  to l o c a l i z e e x c i t a t i o n i n the adjacent double bond, and b)  to s t a b i l i z e an intermediate complex or r a d i c a l species.  Only i n the  * case of _93, was the TT — TT  s t a t e i m p l i c a t e d , being responsible f o r  the observed l a c k of r e a c t i v i t y . A v i a b l e a l t e r n a t e explanation f o r the r e a c t i v i t y of _52 was advanced based on conformational a n a l y s i s ' 0 f the f i v e conformers 2 3  2 5  A - E i n Scheme 10, i t was suggested that conformer C ( i e . s t r u c t u r e 94) would be favored by the bridgehead methyl substituents since only i n t h i s conformation are they not e c l i p s e d .  As a r e s u l t the J2 o r b i t a l  s i t u a t e d on carbon atom 3 approaches r e l a t i v e l y c l o s e l y to the inner C  o  Q  a l l y l i c hydrogen and thus the y-hydrogen a b s t r a c t i o n process  is facilitated.  S i m i l a r reasoning might then account f o r the r e s u l t s  observed i n the cases of compounds 71^ and 73 namely, hydrogen B  39  a b s t r a c t i o n by carbon i s favored by the proximity of the Tr-orbital and the hydrogen i n these r i g i d s t r u c t u r e s .  - 31 3.  Objectives  o f P r e s e n t Research  I t had been demonstrated  previously  e l i m i n a t i n g the symmetry of the p a r e n t r i n g system introduces  (see I n t r o d u c t i o n ) t h a t 4a,5,8,8a-tetrahydronaphthoquinone  ( c f . compound 10) by p l a c i n g a l o n e s u b s t i t u e n t  a t Cg  a r e g i o s e l e c t i v i t y t o the p r o c e s s of B-hydrogen a b s t r a c t i o n ;  the observed p h o t o p r o d u c t s  (Scheme 8) show p r e f e r e n t i a l f o r m a t i o n  of the more s t a b l e b i r a d i c a l s p e c i e s ,  r e s u l t i n g from 8 r a t h e r  8' a b s t r a c t i o n  a l s o of i n t e r e s t t o determine  (compound 36).  i f placing a substituent  I t was  on the ene-dione double bond c o u l d  about such a r e g i o s e l e c t i v e p r o d u c t d i s t r i b u t i o n . 95 and 96^ were i n v e s t i g a t e d .  bring  To t h i s end,  A g a i n , the l o n e s u b s t i t u e n t  36  than  adducts  destroys  0  m o l e c u l a r symmetry i n /9_5 and 96., r e n d e r i n g the p r o c e s s e s o f 8 and abstraction nonequivalent.  There was  t h a t a p h e n y l o r methyl s u b s t i t u e n t  i n a d d i t i o n , the p o s s i b i l i t y  so p o s i t i o n e d would a l t e r  p h o t o c h e m i s t r y from t h a t observed thus f a r i n t h e s e systems Pappas a r g u m e n t * r e g a r d i n g 1  8  8'  t h e e f f e c t of m e t h y l and methoxyl  the (cf.,the substituents).  - 32 The  o r i g i n o f t h e "/-hydrogen a b s t r a c t i o n by enone carbon i n  compound _52 was s t i l l  unclear.  As a l r e a d y  mentioned, two f a c t o r s  could  i n f l u e n c e t h e observed f o r m a t i o n o f 54; a)  t h e p r e s e n c e o f t h e two m e t h y l groups on t h e ene-dione  * chromophore causes a r e v e r s a l o f c l o s e l y i n g n - TT excited  states;  e x c i t e d TT - TT  and  Schaffner?  control;  from  s t a t e , much i n l i n e w i t h t h e p r o p o s a l s o f B a r l t r o p  8  t h e r e a c t i o n p r o c e e d s under t h e i n f l u e n c e o f c o n f o r m a t i o n a l hydrogen a b s t r a c t i o n by c a r b o n i s f a v o r e d  (Scheme 10) which b r i n g s abstractable To  and TT — TT  thus a b s t r a c t i o n by c a r b o n may have o r i g i n a t e d  an  b)  *  t h e enone carbon atom and t h e a l l y l i c  hydrogen i n t o  obtain  proximity.  additional information  compounds 9_7 - 100 were i n v e s t i g a t e d .  0  o  99  by conformer C  i n regard  to these a l t e r n a t i v e s ,  Adduct 97 p o s s e s s e s t h e same  O  o  100, E=C0„Me 4.  - 33 -  chromophore and therefore should also possess s i m i l a r e l e c t r o n i c p r o p e r t i e s as compound 52, while compounds 9_8 - 1 0 0 place  substituents  at the bridgehead p o s i t i o n s and should help to determine the extent of the i n f l u e n c e of conformational c o n t r o l on the photorearrangement. A d d i t i o n a l d e t a i l s w i l l be provided i n the Results and Discussion section.  F i n a l l y , to extend the scope of the photoreaction of the s u b s t i t u t e d r i n g system, compounds 1 0 1 - 1 G 3 were i n v e s t i g a t e d . and  Compounds 1 0 2  1 0 3 are more h i g h l y s u b s t i t u t e d analogues of adduct 42., while  compound 1 0 1 , i n a d d i t i o n to being the C,./C epimer of 1 0 2 , i s a  101 R -Me, R =H 2  analogous to adduct _52. are deferred  Again more s p e c i f i c reasons f o r t h i s study  to the next s e c t i o n .  - 34 -  RESULTS AND DISCUSSION 1.  D i e l s - A l d e r Adducts of Mono-substituted _p_-Benzoquinones  with  2,3-Dimethyl-l,3-butadiene. I t had been demonstrated i n t h i s laboratory that the product d i s t r i b u t i o n r e s u l t i n g from i r r a d i a t i o n of the isoprene-_p_-benzoquinone D i e l s - A l d e r adduct 3_6 r e f l e c t s the s t a b i l i z i n g e f f e c t of the lone methyl substituent on the formation of the two p o s s i b l e b i s - a l l y l i c r a d i c a l intermediates ( c f . I n t r o d u c t i o n ) .  To determine the e f f e c t ,  i f any, a substituent on the ene-dione double bond of the tetrahydronaphthoquinone r i n g system would have on the r e g i o s e l e c t i v i t y of the 3-hydrogen a b s t r a c t i o n process, adducts 95_ and 96 were i n v e s t i g a t e d . Once again, a b s t r a c t i o n of the 8-hydrogen from carbon-atom 5 (Scheme 14) SCHEME 14.  - 35 -  would  give a d i f f e r e n t b i r a d i c a l intermediate  a b s t r a c t i o n from C reflect  A.  Q  o  (105);  the s t a b i l i z i n g  (104) than would  the r a t i o s of products should again  i n f l u e n c e o f the C ^ - s u b s t i t u e n t .  4a3,5,8,8a3-Tetrahydro-2,6,7-trimethyl-1,4-naphthoquinone  (95) .  Adduct 9_5 was s y n t h e s i z e d by t h e method o f Bergmann and Bergmann * 1  (eq. 20).  A m i x t u r e of methyl-p_-benzoquinone  9  and 2 , 3 - d i m e t h y l - l , 3 -  b u t a d i e n e was heated i n a s e a l e d tube a t 110°, r e s u l t i n g i n a 77% O  y i e l d o f adduct 95.  0  95  P h o t o l y s i s o f d i l u t e benzene o r t e r t - b u t y l a l c o h o l  solutions  (2 mg/ml) o f _95_ l e d to the f o r m a t i o n o f f i v e p r o d u c t s 106-110 (eq. 21) i n the r e l a t i v e r a t i o s i n d i c a t e d i n T a b l e I I .  The p h o t o r e a c t i o n  +  0  108  0  (eq. 21)  TABLE I I . R e l a t i v e r a t i o s of Products from P h o t o l y s i s of 95.  Solvent  106  107  108  109  Benzene  3.8  1  2.6  3.4  tert-Butanol  1  9  .  6  -  3  110  1  could be monitored by g l p c , which i n d i c a t e d that a l l of 106-110 were primary photoproducts i n that no i n d u c t i o n period f o r the formation of any product was observed.  However, the r e l a t i v e r a t i o s  of the products, as determined by c u t t i n g out and weighing peaks from the glpc chart paper, were found to vary s l i g h t l y during the course of the r e a c t i o n i n d i c a t i n g that some i n t e r c o n v e r s i o n among the photoproducts was o c c u r r i n g .  Thus the values reported i n Table I I  represent those at the conclusion of the p h o t o l y s i s when no measureable (glpc) amount of 95_ remained. glpc;  Products were i s o l a t e d by preparative  y i e l d s and conditions were not optimized as the main purpose  of the experiment was mechanistic  i n nature.  A l l products were  shown to be isomeric w i t h 9_5 by t h e i r mass spectra and elemental analyses.  Enone a l c o h o l s 106 and 109 both d i s p l a y carbonyl s t r e t c h i n g bands a t 5.93u i n t h e i r i r s p e c t r a , along w i t h small hydroxyl bands at 2.80y.  The most n o t i c e a b l e d i f f e r e n c e s i n t h e i r nmr spectra  -  37  -  ( f i g u r e 3) are the r e l a t i v e chemical s h i f t s of the s i g n a l s due to the  protons and methyl groups s i t u a t e d on the unsaturated carbonyl  p o r t i o n of the molecule. >  I n 106, the C. v i n y l proton resonance i s 4  located at T3.61, downfield from the  proton s i g n a l i n 109 (T4.29),  S i m i l a r l y , the C^, v i n y l methyl s i g n a l i n 109 comes at lower f i e l d (T8.06) than the C  3  methyl of 106 (T8.22).  These s h i f t s are brought about by the p o l a r i z a t i o n " p r e s e n t 5  i n an a,8-unsaturated carbonyl moiety (depicted schematically i n s t r u c t u r e 111) , which r e s u l t s i n a d e s h i e l d i n g of the H which i s bonded to the 8 carbon atom.  proton  As one might expect, t h i s  H 6+  5-  R — C = C H - C = 0 8  iii  a  |  R  d e s h i e l d i n g e f f e c t i s l e s s pronounced i n the case of methyl groups, as they are i n s u l a t e d to a degree by the carbon-carbon bond.  The remainder of the spectra are q u i t e s i m i l a r (Figure 3).  The  v i n y l proton gives r i s e to the m u l t i p l e t occurring at T4.40.  The  broadened doublet at approximately T7 i s assigned to the C, methine. 6  As w i l l be seen, t h i s i s a c h a r a c t e r i s t i c s i g n a l of the enone a l c o h o l  - 38 -  Figure 3.  NMR  Spectra of Enone Alcohols 106 and  109.  s t r u c t u r e w i t h a proton bonded at carbon C,.  The hydroxy1 proton  o  gives r i s e to a s i n g l e t at approximately T7.6, superimposed on a m u l t i p l e t a t t r i b u t e d to the  methine.  The C^Q methylenes give  r i s e to resonances i n the region from T8.4 - 8.6. The s t r u c t u r e of ene-dione 107 was i n d i c a t e d by i t s s i n g l e sharp carbonyl band at 5.70u i n the i r spectrum, c h a r a c t e r i s t i c of a five-membered r i n g c y c l i c ketone?  1  ( f i g u r e 4) showed no s i g n a l below x7.  I  Figure 4.  NMR  •  The nmr spectrum of 107 A narrow m u l t i p l e t at T7.40  I  Spectrum of Ene-dione 107.  was assigned to the C, methine. 6  The C. exo-proton appears as a double 4  - 40 doublet at T7.83 ( c a l c u l a t e d s h i f t ) coupled to the  endo-protori  5 2  (J=18Hz) and (weakly) to the C  methine (J=lHz).  &  showed a doublet at T7.97 ( c a l c u l a t e d ) .  The C  5 2  give r i s e to broad s i n g l e t s at T8.28 and 8.38. at T8.84 i s assigned to the  The g  endo-proton  and C  g  methyls  The sharp s i n g l e t  methyl, thus comfinning the assigned  s t r u c t u r e f o r 107.  The i n t e r a c t i o n between the  exo-proton and  v e r i f i e d by the c o l l a p s e of the doublet on exchange of the  methine  was  m u l t i p l e t a t T7.40 to a broad  exo-proton w i t h deuterium.  long range couplings are f a i r l y common;  Similar  f o r example, they are observed S 3  i n 112, though i n t h i s s p e c i f i c case, a carbonyl carbon i s not  J involved.  = 0.5Hz  They are u s u a l l y very weak (0 - 2Hz) and appear when the  i n t e r a c t i n g protons are arranged i n the "W" 113 . 50  c o n f i g u r a t i o n shown i n  Molecular models r e v e a l that the C. exo- and C. protons i n 4 o  diketone 107 assume j u s t t h i s c o n f i g u r a t i o n .  113  The above-mentioned  exchange of the  exo-proton w i t h deuterium-  was brought about by t r e a t i n g a s o l u t i o n of 107, i n an nmr tube w i t h  - 41 -  a 2N s o l u t i o n o f potassium h y d r o x i d e i n d e u t e r i u m o x i d e .  After  p e r i o d i c s h a k i n g over a p e r i o d o f e i g h t h o u r s , t h e nmr spectrum was retaken  ( f i g u r e 4 ) , which shows, by t h e t o t a l d i s a p p e a r a n c e o f t h e  d o u b l e d o u b l e t a t T7.79, t h e s e l e c t i v e exchange o f t h e In a d d i t i o n t o t h e noted change i n t h e  exo-proton.  p r o t o n resonance, t h e o  d o u b l e t a t Tl.91  (due t o  endo-proton)  c o l l a p s e s t o a broad  triplet.  No o t h e r change i s observed i n t h e nmr spectrum.  P r o d u c t 110 f e a t u r e s a s i n g l e i r c a r b o n y l band a t 5.72u. I t s nmr  spectrum  ( f i g u r e 5) shows, i n a d d i t i o n t o v i n y l methyl  T—r- —'— —H 1  F i g u r e 5.  NMR Spectrum  1  r  ' i  '  i—  1 1  •i  1  '  signals  r— —T 1  o f Ene-dione 1 1 0 .  a t T8.34 and T8.47, a d o u b l e t a t T8.95, a s s i g n e d t o t h e  m e t h y l and  c o u p l e d t o the'C. p r o t o n w i t h a c o u p l i n g c o n s t a n t o f 7.5Hz.  This  - 42 doublet again d i s t i n g u i s h e s s t r u c t u r e 110 from that of dione 107. While the  proton resonance can not be discerned, the remainder  of the spectrum c l o s e l y resembles that of ene-dione 18 ** 5  Ene-dione 108 e x h i b i t s an i r spectrum w i t h two carbonyl bands at 5.68 and 5.80u, analogous to the i r of ene-dione 19J  5 > 2 5  which  i n d i c a t e s the presence of a five-membered and a six-membered c y c l i c ketone  51  The u l t r a v i o l e t spectrum a l s o supports  s t r u c t u r e 108  by showing absorptions at 294 nm (e 481) and 307 nm (e 426).  Such  enhanced e x t i n c t i o n c o e f f i c i e n t s have been f o u n d t o be c h a r a c t e r i s t i c 55  of most 8>Y unsaturated ketones, such as 108, and have a l s o been -  observed p r e v i o u s l y i n the uv spectra of analogous products _13_ and  The nmr spectrum, shown i n f i g u r e 6, features a broad doublet at T4.42 (J=7Hz) due to the C  6  r  methine.  v i n y l proton which i s coupled to the  The double doublet at lb.11 i s a t t r i b u t e d to the C, proton, b  coupled to the  v i n y l and to the  methine (J=8Hz).  The  exo and  endo-protons each d i s p l a y doublets w i t h mutual coupling constants of • 17.5Hz, and appear at T7.14 and T8.15 r e s p e c t i v e l y .  The Cg v i n y l methyl  shows a s i n g l e t at T8.12, w h i l e the C^ and C^ methyls give r i s e to sharp s i n g l e t s at T8.73 and T9.02.  The presence of these t e r t i a r y methyl  s i n g l e t s thus r u l e s out the a l t e r n a t i v e s t r u c t u r e 114 f o r t h i s product,  - 43 -  Figure 6.  NMR Spectrum of Ene-dione 108.  which would g i v e r i s e to s i n g l e t and doublet resonances f o r the methyl groups (compare again 107 and 110).  A d d i t i o n a l evidence f o r the s t r u c t u r e s of products 106-110 w a s obtained from an i n t e r e s t i n g s e r i e s of thermal and photochemical rearrangements, shown i n Scheme 15. Thus, sealed tube thermolysis  - 44  -  SCHEME 15.  of 106 at 200° gave 107, w h i l e thermolysis of 109 under i d e n t i c a l conditions gave 110. [3,3]  Both transformations represent f o r m a l l y allowed  s u p r a f a c i a l sigmatropic rearrangements\ although 8  a stepwise  mechanism i s a l s o p o s s i b l e .  Sealed tube thermolysis of 108 gave a high y i e l d of 107, a formally d i s a l l o w e d  1 8  [l ,3] s u p r a f a c i a l sigmatropic rearrangement  20  The formation of 108 on p h o t o l y s i s of 106 represents an allowed [l,3] sigmatropic rearrangement, although the work of C a r g i l l ( c f . compound 1 9  29) presents an example where such a transformation i n nonconcerted. On the other hand, the 106 ^ 107 and 1 0 9 ^ h  disallowed photochemical  [3,3]  1 10 conversions are f o r m a l l y  rearrangementsJ  8  an analogous  transformation, that of 33 to _34_ has been observed by Schaffner and  -  45  -  co-workers (see Introduction). 21  The r e s u l t s thus p a r a l l e l those obtained  f o r the dimethyl  products derived from adduct _17_ (see I n t r o d u c t i o n ) .  Once again,  l i k e compound _L8, ene-diones 107 and 110, which feature the same r i n g system as compound _18, appear to be the thermodynamically most stable.  The mechanism f o r the formation of products 106-110 from 9 5 very l i k e l y involves i n i t i a l 3-hydrogen a b s t r a c t i o n from e i t h e r C  c  J  or C , w i t h formation of b i r a d i c a l intermediates  115 and 116  D  o  r e s p e c t i v e l y (Scheme 16). Subsequent bond formation  (and k e t o n i z a t i o n  SCHEME 16.  116 A,7-hoiVrHnf>  115  106  , kp.tonizatiQii» 107  s-hond-ing \ 116  2,7-hond-ing 1 ,6-bnnd-tng a-brmding  ketonisatipn  t  y  y  >  108  109 kpfon-j z a t l o n  >  110  0  -46  -  i n the cases of 107, 108 and 110) would then account f o r the observed products.  As w e l l , the product d i s t r i b u t i o n suggests the p r e f e r e n t i a l  formation of intermediate 115.  TABLE I I I .  This i s shown i n Table I I I .  R e l a t i v e Ratios of Products A r i s i n g from Intermediates 115 and  116.  Solvent  115  116  Benzene  2.2  1  tert-Butanol  2.6  1  The reason why ene-dione 114, which could be formed by 3,6-bonding i n 116 (eq. 22), i s not observed i s not r e a d i l y apparent.  No doubt  (eq.  22)  (not formed) r e l a t e d to t h i s i s the f a c t that enone-alcohol 109, on p h o t o l y s i s i n benzene, d i d not rearrange to 116 nor to any other product. behavior i s observed only f o r 109;  Such  enone a l c o h o l s 106 and /20 r e a d i l y  photoisomerize i n benzene to the corresponding compounds 108 and 19.  B.  (96).  6,7-Dimethyl-2-phenyl-4a3,5,8,8a3-tetrahydro-1,4-naphthoquinone  The synthesis of adduct /96 was performed  i n a manner s i m i l a r to  of 95^, a f t e r the method of Bergmann and Bergmann^ a mixture 9  phenyl-j)-benzoquinone and 2,3-dimethyl-l,3-butadiene was  of  thermolyzed  that  -  47  -  i n a sealed Pyrex tube f o r one hour at 100°C (eq. 23).  100° 1 hour sealed tube The photochemical r e a c t i o n of 9j6 was monitored by observing changes i n the i r spectrum of the r e a c t i o n mixture as the r e a c t i o n progressed.  This showed a r a p i d change i n the region below 6.5]i  on i r r a d i a t i o n i n e i t h e r benzene or t e r t - b u t a n o l , accompanied by the appearance and growth of a carbonyl band at 5.70u, at the expense of the s t a r t i n g m a t e r i a l carbonyl at 5.93]i u n t i l the 5.70y absorption remained the lone v i s i b l e carbonyl band.  Workup by column chromatography  was accompanied by extensive decomposition as i n d i c a t e d by a band of black m a t e r i a l which remained at the top of the column.  However,  the i s o l a t i o n of a s i n g l e photoproduct was achieved i n about 30 35% y i e l d .  This product was assigned the s t r u c t u r e 117 on the b a s i s of  s p e c t r a l data (eq. 24).  * o  -  •  Ene-dione 117, i n a d d i t i o n to d i s p l a y i n g an i r spectrum  -  (eq  24)  featuring  a 5.70y carbonyl band, e x h i b i t s the nmr spectrum shown i n f i g u r e 7.  -  Figure 7.  48  -  NMR Spectrum of Ene-dione 117.  The double doublet at T7.06 ( c a l c u l a t e d ) 52  exo-proton, coupled to the methine (J=1.5Hz).  The  also as a doublet (J=18Hz).  i s assigned to the  endo-proton (J=18Hz) and weakly to the endo s i g n a l occurs  a f x7.62 ( c a l c u l a t e d ) ;  V i n y l methyls appear at T8.32 and T8.69.  The nmr spectrum thus favors s t r u c t u r e 1_17 over that of 118, a p o s s i b l e a l t e r n a t i v e f o r the photoproduct. No s i g n a l appears at  5 2  lower f i e l d than T6.88, except f o r the phenyl protons ( s i n g l e t at T2.64).  This would not be expected f o r s t r u c t u r e 118.  The C.  proton i n 118 i s a to a carbonyl, t e r t i a r y and b e n z y l i c , and thus should appear at a lower f i e l d t h a n the b e n z y l i c a-methylene protons 5 0  i n d i b e n z y l ketone 119, which show a resonance at T6.3  56  0 II  Ph - CH  2  - C - CH  2  - Ph  119 Further support f o r s t r u c t u r e 117 was found when a s o l u t i o n of 117 was treated w i t h a 1.2N hydroxide i n an nmr tube. 18 and 107, the  deuterium oxide s o l u t i o n of potassium As was the case previously w i t h ene-diones  exo-proton was s e l e c t i v e l y exchanged f o r deuterium.  The r e s u l t i n g changes i n the nmr spectrum ( f i g u r e 7) are the disappearance of the double doublet at T7.06 and a c o l l a p s e of the doublet at T7.62 (C^ endo) to a broad s i n g l e t .  I t was p o s s i b l e to i s o l a t e a second photoproduct, i n a d d i t i o n to 117, from the p h o t o l y s i s of 96 i n benzene i f the r e a c t i o n was  interrupted  when the i n t e n s i t i e s of the i r carbonyl bands at 5.70 and 5.93y were  - 50 about equal.  Column chromatography r e s u l t e d i n a small quantity  (< 20%) of an o i l which showed a small hydroxyl absorption i n the i r as w e l l as a 5.93y carbonyl. i n the nmr  The v i n y l proton region (T3-4.5)  spectrum resembled that of the mixture of enone a l c o h o l s  106 and 109, and i t was  t e n t a t i v e l y concluded that a mixture of  isomeric enone a l c o h o l s 120 and 121 was present i n a r a t i o of about 6:1 based .on the nmr  i n t e g r a t i o n of the v i n y l proton s i g n a l s .  120  121  Rechromatography of the mixture, which was  again accompanied by  decomposition, r e s u l t e d i n only p a r t i a l separation;  120 and  121  were i s o l a t e d as crude s o l i d s i n very low y i e l d .  The main d i f f e r e n c e i n the nmr  spectra of 120 and 121  ( f i g u r e 8)  i s , as i n the case of 106 and 109, the r e l a t i v e p o s i t i o n of the C^ v i n y l (T3.20) i n 120 and the C  3  v i n y l (T4.03) i n 121.  Again,  the d e s h i e l d i n g e f f e c t p r e v i o u s l y discussed f o r a,B-unsaturated ketones i s r e s p o n s i b l e f o r the downfield p o s i t i o n of the v i n y l resonance i n 120 ( c f . s t r u c t u r e 111).  The l a c k of s u f f i c i e n t m a t e r i a l prevented  f u r t h e r study of compounds 120 and 121.  •  The formation of 117, 120 and 121 can be explained by the $-hydrogea  - 51 -  Figure 8.  NMR  Spectra of Enone Alcohols 120 and 1 2 1 .  a b s t r a c t i o n mechanism shown i n Scheme 17, i n v o l v i n g b i r a d i c a l i n t e r mediate 122, i n the case of 117 and 120, and the species 123 i n the case of 121. The formation of 117 from 122 was shown to involve the SCHEME 17. O  117  intermediacy  of enol 124 by the observation that p h o t o l y s i s of adduct  96 i n tert-butanol-0-d l e d to deuterio-117 (92% i n c o r p o r a t i o n of deuterium, c a l c u l a t e d from mass spectrum - see Appendix f o r c a l c u l a t i o n s ) . The nmr spectrum of deutereo-117 was i d e n t i c a l to that of the product of the base-catalyzed  J)^0 exchange r e a c t i o n and showed that the  deuterium was l o c a t e d e x c l u s i v e l y a t the C^ e x o - p o s i t i o n .  While no q u a n t i t a t i v e information i s a v a i l a b l e , i t i s obvious that the photochemistry of 96_ proceeds almost e x c l u s i v e l y v i a b i r a d i c a l 122, although the low y i e l d s of products obtained somewhat from t h i s conclusion.  detract  Furthermore, i t seems that some  - 53 subtle e f f e c t s are operating i n t h i s instance since the major product i n benzene i s 117 and not 125, which possesses the r i n g s t r u c t u r e found i n products emerging from p h o t o l y s i s of s e v e r a l D i e l s - A l d e r adducts i n benzene, such as 1_9 and 108.  At no time was the presence of  125 detected.  C. Of  D i s c u s s i o n of Photochemistry of 9_5 and 96. the two b i r a d i c a l s 104 and 105 (shown i n Scheme 14) which  would r e s u l t from a 3-hydrogen a b s t r a c t i o n from C  c  5  and C , o Q  respectively  i n adduct 9_5 or 9_6, i t was a n t i c i p a t e d that 104, i n which the s u b s t i t u e n t occupies the terminal p o s i t i o n of the a l l y l r a d i c a l and thus exerts a s t a b i l i z i n g i n f l u e n c e , would be formed i n preference to  105, where the s u b s t i t u e n t i s s i t u a t e d at the c e n t r a l carbon of the  a l l y l system.  The highest occupied molecular o r b i t a l of an a l l y l  r a d i c a l has a node at the c e n t r a l carbon atom;  Hence a substituent  located there would be expected to have very l i t t l e s t a b i l i z i n g (or d e s t a b i l i z i n g ) e f f e c t on the species.  On the other hand, i t has  been shown through thermochemical measurements that 57  the 1 — m e t h y l a l l y l  r a d i c a l i s more s t a b l e than an unsubstituted a l l y l r a d i c a l by 2.5 kcal.mole.  - 54  -  The photochemistry of 9_5, l i k e J36 ( I n t r o d u c t i o n ) , i s found to be i n accord w i t h these considerations.  The data shown i n Table I I I  reveals that products a r i s i n g from b i r a d i c a l 114, Scheme 16 ( i e . 104, R=Me), are p r e f e r r e d by at l e a s t a two-to-one r a t i o over those  formed from 115  ( i e . 1_05, R=Me).  An even greater preference  f o r species 104 i s observed i n the  photochemistry of /9_6_, where only traces of m a t e r i a l o r i g i n a t i n g from 105 could be detected.  This r e s u l t i s i n accord w i t h the expected  greater s t a b i l i z i n g i n f l u e n c e of a phenyl group s u b s t i t u t e d at an a l l y l r a d i c a l terminus, as i n 104, R=Ph, due to the extensive d e r e a l i z a t i o n of e l e c t r o n density i n t o the aromatic r i n g .  No thermochemical data are a v a i l a b l e f o r the 1 - p h e n y l a l l y l radical;  however, i t i s known that i n c r e a s i n g the d e r e a l i z a t i o n  of e l e c t r o n density r e s u l t s i n an increase i n r a d i c a l s t a b i l i t y . example, pentadienyl r a d i c a l (126) i s more s t a b l e t h a n 5  r a d i c a l by 2.5 k c a l stable  For  1-methylallyl  mole.* Furthermore, benzyl r a d i c a l (127) i s more -1  than methyl r a d i c a l by 15 k c a l mole.  126  127  The e f f e c t of i n t r o d u c i n g a s i n g l e substituent on the ene-dione double bond i s l i m i t e d , however, to t h i s observed d i r e c t i n g i n f l u e n c e i n product d i s t r i b u t i o n .  That the photoproducts formed from 95_ and j>6  - 55 -  possess the same b a s i c r i n g systems as do p r o d u c t s 18-20, d e r i v e d from the u n s u b s t i t u t e d adduct 17_, s u g g e s t s that a s i n g l e  substituent  does not a l t e r , the e x c i t e d s t a t e e n e r g i e s of the t e t r a h y d r o n a p h t h o q u i n o n e ring  system, as proposed f o r s u b s t i t u t e d p_-benzoquinones  by  Barltrop  4 7  (see i n t r o d u c t i o n ) .  2.  D i e l s - A l d e r Adduct o f 2,3-Dimethyl-j>-benzoquinone  with  2,3-  D i m e t h y l - l , 3 - b u t a d i e n e (97). I t was  noted i n the I n t r o d u c t i o n t h a t the d i v e r g e n t p h o t o c h e m i c a l  r e a c t i v i t y of adduct 52_ might be due to t h e p r e s e n c e of the two m e t h y l groups on the ene-dione chromophore of the m o l e c u l e which a l t e r e d or reversed ( i e . n — TT  v s TT -  the e n e r g i e s of the r e a c t i v e e x c i t e d s t a t e s TT ).  To t e s t  involved  t h i s h y p o t h e s i s , adduct 97_, which  p o s s e s s e s the same d i m e t h y l s u b s t i t u e n t s on the chromophore as d i d 52, was  investigated.  F o r m a t i o n o f compound 128 from 97_, a p r o c e s s  analogous to the 52 -»- _54 c o n v e r s i o n , would  Adduct  s e r v e to c o n f i r m such an  effect.  97_, 4a$,5,8,8a8-tetrahydro-2,3,6,7-tetramethy 1-1,4-  naphthoquinone, was as summarized  s y n t h e s i z e d , u s i n g t h e method o f F i e s e r and Chang  i n Scheme 18.  to quinone 129 was  The o x i d a t i o n o f 5 9  2,3-dimethylaniline  performed u s i n g " a c t i v e " manganese d i o x i d e , which  - 56 -  SCHEME 18.  129  97  was prepared j u s t p r i o r to use by the method of Attenburrow, et a l  6 0  Refluxing .an ethanolic s o l u t i o n of 129 and diene overnight y i e l d e d the desired adduct 97.  The p h o t o l y s i s of 97_ i n benzene was monitored by glpc which showed the formation of a s i n g l e photoproduct which proved to be i n e r t to prolonged i r r a d i a t i o n . Column chromatography r e s u l t e d i n a 25% y i a l d c f a c o l o r l e s s c r y s t a l l i n e isomer of 97_ (mass spectrum, elemental a n a l y s i s ) which was assigned s t r u c t u r e 130 on the b a s i s of i t s s p e c t r a l properties which were s i m i l a r to those of enone a l c o h o l 20.  (eq. 25)  130 Compound 130 e x h i b i t s an i r (KBr) spectrum w i t h a hydroxyl band .. at 2.94y and an a,3-unsaturated carbonyl s t r e t c h a t 6.05y (KBr).  The  nmr spectrum of 130 ( f i g u r e 9) features a s i n g l e v i n y l resonance at T4.42  - 57 -  (C^ proton) and a s i n g l e t at T7.70 which disappears upon a d d i t i o n of deuterium oxide, i n d i c a t i n g i t i s due to the hydroxyl proton.  Three  v i n y l methyls appear at T8.16, 8.25 and 8.30, w h i l e the lone t e r t i a r y methyl (at C^) comes at T8.93.  The doublet at x7.13, again c h a r a c t e r i s t i c  of the enone a l c o h o l s t r u c t u r e ( c f . nmr of 106 and 109), i s assigned to the C. methine, w h i l e the m u l t i p l e t at T7.84 i s a t t r i b u t e d to 6 the  methine.  The  methylenes are nearly magnetically equivalent,  as i n d i c a t e d by t h e i r resonances at T8.59 and 8.65.  Figure 9 shows  the nmr spectrum of deuterated 130.  Figure 9.  NMR Spectrum of 130.  I r r a d i a t i o n of 97_ i n t e r t - b u t a n o l l e d to i n i t i a l formation of 130 plus a second minor photoproduct 131, as detected by g l p c .  In  this  -58  -  instance, however, enone a l c o h o l 130 suffered a secondary photochemical transformation to 131, coincident with the r e a c t i o n of 9_7, u n t i l the 131:130 r a t i o was 2:1 when no glpc detectable quantity of 97_ remained. In a separate experiment, i r r a d i a t i o n of 130 i n t e r t - b u t a n o l r e s u l t e d i n complete transformation to 131.  tert-butanol The s t r u c t u r e of photoproduct 131 was i n d i c a t e d by i t s i r carbonyl band at 5.74y, i n d i c a t i n g a five-menbered r i n g ketone, and by i t s nmr spectrum, shown i n f i g u r e 10.  The Cg and C^ v i n y l methyl  s i g n a l s come at T8.25 and 8.40, w h i l e the C^ t e r t i a r y methyl shows a s i n g l e t at T8.85.  The doublet (J=7Hz) at T9.09 i s a t t r i b u t e d  to the C^ methyl coupled to the C^ methine which should appear as a quartet and i s p a r t l y v i s i b l e at T7.73, coupled to the C^ methyl (J=7Hz).  The small coupling superimposed on t h i s quartet i s l i k e l y  due to long range coupling to the C, methine, as was the case w i t h o the analogous ene-dione 107. C^ methine.  The s i g n a l at T7.24 i s assigned to the  The remaining protons form a complex m u l t i p l e t i n the  T7.5 - 7.8 region. Reaction of a CDCl^ s o l u t i o n of 131 w i t h a 1.2N deuterium oxide  - 59 -  Figure 10.  NMR  Spectrum of Ene-dione  131.  s o l u t i o n of potassium hydroxide l e d to the exchange of the proton f o r deuterium, which suggested that the proton"was i n the exo c o n f i g u r a t i o n (see I n t r o d u c t i o n ) .  The r e a c t i o n was very slow  however, r e q u i r i n g two weeks f o r complete exchange of the proton to occur at 25°.  In a d d i t i o n to the disappearance of the T7.73 s i g n a l  (C^ p r o t o n ) , other nmr changes noted ( f i g u r e 10) were the c o l l a p s e of the doublet at T9.09 to a broad s i n g l e t , and a s i m p l i f i c a t i o n of the s i g n a l at x7.24 (C- methine). o again v e r i f i e d the existence of C A  «  This l a t t e r observation once long range coupling.  - 60 The mechanism f o r the formation of 130 and 131 i s given i n Scheme 19, and i n v o l v e s an i n i t i a l 8-hydrogen a b s t r a c t i o n from e i t h e r C,. or C  Q  8  to give the b i s - a l l y l i c r a d i c a l intermediate 132.  I n benzene  SCHEME 19.  1,6-bonding  >  benzene or tert-butano 130  hv.  3,8-bonding  tert-butanol  ketonization  > 131  1,6-bonding then leads to d i r e c t formation of 130.  In t e r t - b u t a n o l ,  i n a d d i t i o n to formation of 130, a bond c l o s u r e between p o s i t i o n s 3 and 8 l i k e l y leads to enol 133 which then ketonizes to give 131. As w e l l , the 130 -+ 131 conversion i n t e r t - b u t a n o l i s observed, the formal r e s u l t of a photochemical  [3,3] sigmatropic rearrangement,  which i s t h e o r e t i c a l l y forbidden on the b a s i s of o r b i t a l symmetry considerations\  8  -  6 1 -  The f a c t that compound 131 i s formed i n the p h o t o l y s i s of 97, and not 128, suggests that i n the case of adduct _52, ene-dione double bond s u b s t i t u t i o n alone does not account f o r the photochemical formation of 54.  3.  D i e l s - A l d e r Adducts w i t h Bridgehead Substituents. On the b a s i s of the r e s u l t s obtained f o r adduct 9_7, i t was next  of i n t e r e s t to determine the r o l e of s u b s t i t u e n t s bonded to carbon atoms C.  4a  and C„ of the tetrahydronaphthoquinone r i n g system oa  ( i e . the bridgehead p o s i t i o n s ) , and thus to t e s t the second hypothesis advanced f o r the photochemical r e a c t i v i t y of 52:  v i z . , the theory  based on the conformational e f f e c t (see Introduction) of these substituents.  To t h i s end, the photochemistry of adducts 98-100 was i n v e s t i g a t e d . The choice of these adducts was determined by t h e i r ease of synthesis and  0  99  Rj = CN;  R  2  = Cl  134  R  x  = Me;  R  2  = H  by the r e l a t i v e s t e r i c bulk or s i z e of R^. The s i z e of a given s u b s t i t u e n t was t a k e n a s i t s A v a l u e ^  l a  i e . , i t s e f f e c t on the  e q u i l i b r i u m constant K f o r the process shown i n f i g u r e 11, that of cyclohexane c h a i r i n v e r s i o n .  Figure 11.  Table IV l i s t s the conformational free energy  Cyclohexane Chair I n v e r s i o n .  d i f f e r e n c e s (AG°) ^ Corresponding to the constant K. To a f i r s t 1  TABLE IV.  Conformational Free Energy D i f f e r e n c e s . Group (X) H  CN CO Me Me  -AG° ( k c a l mole" ) 0 0.15 - 0.25 1.1 1.5 - 2.1  approximation these values were regarded as i n d i c a t i v e of the r e l a t i v e preference f o r the D i e l s - A l d e r adducts bearing s u b s t i t u e n t X at the bridgehead p o s i t i o n s to assume the t w i s t conformation (conformer CJ, Scheme 10) i n preference to the other four conformers (see I n t r o d u c t i o n , Scheme 10). Adducts J38, j?9, 100 and 134 thus formed a s e r i e s of compounds t o t e s t t h i s e f f e c t .  As i t turned out, compound 134 was  u n a v a i l a b l e f o r study due to d i f f i c u l t i e s encountered i n i t s attempted synthesis.  - 63 -  A.  4a3,8a8-Dicyano-6,7-dimethyl-4a,5,8,8a-tetrahydro-l,4naphthoquinone (98).  Adduct 9J3 was synthesized as o u t l i n e d i n Scheme 20, The o x i d a t i o n of 2,3-dicyanohydroquinone was accomplished using a SCHEME 20.  98  135  v a r i a n t of the method reported by B r o o k  62  Nitrogen d i o x i d e was f i r s t  condensed i n t o a f l a s k at -196°C, then added dropwise to a r a p i d l y s t i r r e d suspension of dicyanohydroquinone i n carbon t e t r a c h l o r i d e . The o x i d a t i o n to 135 was complete i n t h i r t y minutes, and the y i e l d of 135 was q u a n t i t a t i v e .  The D i e l s - A l d e r r e a c t i o n was performed i n the  manner of A n s e l l , et a l a n d r e s u l t e d i n a 75% y i e l d of adduct 98 6 3  as l a r g e , pale yellow prisms.  The course of the p h o t o l y s i s of 9j8 was followed by observing the disappearance of the peak due to s t a r t i n g m a t e r i a l ( i e . 98) on glpc.  I n benzene s o l u t i o n , 98^ reacted upon i r r a d i a t i o n to g i v e  a complex mixture of many products (as i n d i c a t e d by t i c ) , none o f which could be i s o l a t e d i n amounts s u f f i c i e n t f o r c h a r a c t e r i z a t i o n .  - 64 -  P h o t o l y s i s i n t e r t - b u t a n o l s o l u t i o n , however, r e s u l t e d  in.the  f o r m a t i o n of two p r o d u c t s 3.36 and 137, which were separated by chromatography. solid  The f i r s t was  i n 50% y i e l d  and was  obtained  identified  e l e m e n t a l a n a l y s i s ) enone a l c o h o l similarities  Product hydroxyl  to compound  as the i s o m e r i c  crystalline (mass  spectrum,  136 on the b a s i s of i t s s p e c t r a l  20.  136 e x h i b i t s a s o l i d  (2.90u), cyano  as a c o l o r l e s s  column  state  (KBr) i r spectrum f e a t u r i n g  (4.41y) and c a r b o n y l  (5.87y) bands.  I n the  case of the c a r b o n y l s t r e t c h , the band p o s i t i o n i s s l i g h t l y  shifted  to lower wavelength t h a n n o r m a l l y encountered f o r the a , B - u n s a t u r a t e d c a r b o n y l band i n enone a l c o h o l s of s i m i l a r s t r u c t u r e c a r b o n y l a t 5.90y).  T h i s may  of the cyano groups p r e s e n t . shift  be a t t r i b u t e d  ( c f . 20,  to the i n d u c t i v e  This i s i l l u s t r a t e d  effect  by t h e 0.06y  to lower wavelength o f the c a r b o n y l band i n compound 139 as  compared  t o t h a t i n 138^ ** CH C0 CH CH 3  2  138, v  The nmr  2  c  =  Q  CN-CH C0 CH CH 2  3  = 5.77y  139, v  2  c  =  Q  2  =  5.71y  spectrum of 136 f e a t u r e s an AB system f o r the v i n y l  p r o t o n s , as shown i n f i g u r e  12.  As i n the cases of compounds  106  5 1  -  Figure 12.  65  -  NMR Spectrum of Enone A l c o h o l 136.  and 109, p o l a r i z a t i o n i n the a,8-unsaturated carbonyl p o r t i o n of the molecule r e s u l t s i n the observed chemical s h i f t s of the C, and  (T3.69) protons.  (T2.99)  The mutual coupling constant i s 10Hz.  m u l t i p l e t at T4.07 i s assigned to the  The  v i n y l , w h i l e a broad s i n g l e t  at T7.19, which disappeared on adding deuterium oxide, i s a t t r i b u t e d to the h y d r o x y l proton. (J=13Hz) around T7.7; resonances.  One of the C^Q methylenes shows a doublet the other i s masked by the acetone-d^ solvent  The Cg v i n y l methyl comes at T8.03, a narrow doublet  (J=1.5Hz) coupled weakly to the C  7  vinyl v i a a l l y l i c coupling  5 0  - 66 -  w h i l e the Cg methyl shows a sharp s i n g l e t a t T8.73.  The second photoproduct 137, i s o l a t e d as a c o l o r l e s s o i l , proved to be a secondary photoproduct of 136, as demonstrated by the complete conversion of 136 to 137 upon i r r a d i a t i o n i n t e r t - b u t a n o l .  The i r  spectrum of 137 shows a cyano band at 4.42y and two carbonyl bands at 5.65y and 5.80y, p o s s i b l y i n d i c a t i n g the presence of a five-membered r i n g ketone (inductive e f f e c t of cyano group!) and an ester c a r b o n y l The nmr spectrum shown i n f i g u r e 13 features a sharp s i n g l e t a t  Figure 13.  NMR Spectrum of 137.  51  -  67  -  T 8 . 5 3 , p o s s i b l y due t o t h e p r o t o n s from a t e r t - b u t y l e s t e r  v i n y l m e t h y l s appear as s m a l l m u l t i p l e t s a t T8.29 and 8.38. other  s i g n a l s c o u l d be a s s i g n e d  Support f o r t h e p r o p o s a l derived  Two  6 5  No  w i t h any c e r t a i n t y .  that  137 was a t e r t - b u t y l e s t e r  from 136 came i n t h e mass spectrum o f 137 which showed a  p a r e n t ion" a t 314 amu i n d i c a t i n g t h a t one m o l e c u l e o f t e r t - b u t a n o l , the  s o l v e n t , had been i n c o r p o r a t e d  Several failure.  i n t o the molecular  formula.  attempts t o p u r i f y 137 o r t o form d e r i v a t i v e s met w i t h  As a r e s u l t , a s t r u c t u r e c o u l d n o t be proposed f o r t h i s  molecule.  I t seems, however, t h a t  137 i s n o t s i m i l a r t o any p r o d u c t  thus f a r encountered and, w h i l e i n t e r e s t i n g i n i t s own r i g h t , not  shed any a d d i t i o n a l i n f o r m a t i o n  substituents  does  on t h e r o l e o f b r i d g e h e a d  i n D i e l s - A l d e r adduct p h o t o c h e m i s t r y .  For t h i s  reason,  compound 137 was s e t a s i d e .  The and  p h o t o c h e m i s t r y o f 98_ was a l s o i n v e s t i g a t e d u s i n g  methanol as s o l v e n t s .  was enone a l c o h o l 136. to i n i t i a l  acetonitrile  In e i t h e r case, the only product  The f o r m a t i o n  o f enone a l c o h o l 136 i s l i k e l y due  3-hydrogen a b s t r a c t i o n , l e a d i n g  to b i r a d i c a l species  (Scheme 2 1 ) , which then s u f f e r s 1,6 bond c l o s u r e Secondary p h o t o l y s i s o f 136 g r a d u a l l y  obtained  leads  to g i v e  to 137.  140  136 d i r e c t l y .  - 68 -  SCHEME 21.  1,6-bonding  137 136 B.  2,3-Dichloro-4a8,8aB-dicyano-6,7-dimethyl-4a,5,8,8atetrahydro-1,4-naphthoquinone (99).  In an attempt to p o s s i b l y f u r t h e r c h a r a c t e r i z e a photoproduct analogous to the unknown photoisomer 137, D i e l s - A l d e r adduct 99_ was next studied.  I t s synthesis i s shown i n Scheme Z2. Following the  procedure of Walker and Waughf 2,3-dicyanohydroquinone 6  SCHEME 22.  was o x i d i z e d  - 69 to 2,3-dichloro-5,6-dicyanoquinone n i t r i c acid.  (141) on treatment w i t h concentrated  Excess 2,3-dimethyl-l,3-butadiene was then added to a  methanolic s o l u t i o n of 141, r e s u l t i n g i n an exothermic  reaction  and formation of 9_9 a f t e r j u s t ten minutes.  P h o t o l y s i s of 9_9 i n benzene again l e d to a complex mixture of many products ( t i c ) , none of which could be i s o l a t e d .  Irradiation  i n t e r t - b u t a n o l r e s u l t e d i n a 42% i s o l a t e d y i e l d of a s i n g l e  photoisomer  142.  142 Enone a l c o h o l 142 i s a c o l o r l e s s c r y s t a l l i n e s o l i d which e x h i b i t s an i r spectrum f e a t u r i n g hydroxyl (2.92y), cyano (4.44y), carbonyl (5.90y) and carbon-chlorine (12.45y) s t r e t c h i n g bands. shows a s i n g l e v i n y l s i g n a l at T4.07 due to the methylenes g i v e an AB system at T7.47 and T7.81 w i t h a coupling constant of 14Hz.  I t s nmr  proton.  The C^Q  (calculated v a l u e s ) 5 2  The hydroxyl proton which can be  exchanged by adding deuterium oxide, shows a s i n g l e t at T7.07. narrow doublet (J=1.5Hz) at T8.02 i s a t t r i b u t e d to the C coupled to the s i n g l e t at T8.67.  spectrum  v i n y l v i a a l l y l i c coupling.  The  g  A  methyl,  methyl i s a  Figure 14 shows the nmr spectrum of 142-0-d.  - 70 -  i )0  ;--  r~  r  400  -,  I  i  300  I  I  I 'I  700  ' 'I  \-r~TT  0 hi  100  r  Figure  14.  The  NKR  Spectrum of Enone A l c o h o l  formation  of  142  likely  involves  142. the  B-hydrogen a b s t r a c t i o n  mechanism w h i c h g i v e s a b i r a d i c a l analogous to 140 no o t h e r  p r o d u c t except 142  t h a t of j)8, o f f e r e d v e r y  little  of b r i d g e h e a d s u b s t i t u e n t s c l e a r r e s u l t was isomeric such as  that  formed, the p h o t o l y s i s of 99_, information  regarding  on m o l e c u l a r c o n f o r m a t i o n .  the The  As like  influence only  i n t e r t - b u t a n o l , the o n l y p r o d u c t formed i s  enone a l c o h o l . that present  was  (Scheme 21).  No  the  p r o d u c t i n c o r p o r a t i n g an ene-dione s t r u c t u r e  i n LB, _19 or 54 was  ever o b s e r v e d .  - 71 C.  4aB,8aB-Dicarbomethoxy-6,7-dimethyl-4a,5,8,8a-tetrahydro1,4-naphthoquinone  (100) .  Adduct 100 was synthesized according to the procedure of A n s e l l , et a l ' w h i c h i s summarized i n Scheme 23. 6 7  6 3  The D i e l s - A l d e r r e a c t i o n  SCHEME 23.  of 145 w i t h 2,3-dimethyl-l,3-butadiene gave, i n a d d i t i o n to 100, compound 146 as w e l l , which i n part accounted f o r the low y i e l d (25%) of 200 i n t h i s step ( y i e l d of L46 was 25%).  I r r a d i a t i o n of 100 i n benzene s o l u t i o n r e s u l t e d i n the formation of two products, i d e n t i f i e d as 147 and 148 (eq. 27) i n a combined y i e l d of 65%.  (eq.  147  148  0  27)  - 72 Enone a l c o h o l 147 features i r carbonyl bands at 5.80y (ester) and 5.90y (a,3-unsaturated  ketone).  The nmr spectrum i s q u i t e  s i m i l a r to that of the analogous enone a l c o h o l s p r e v i o u s l y reported (for example, 136, f i g u r e 12).  The  and  v i n y l s each show a  doublet (AB system) w i t h a coupling constant of 10Hz, located ( c a l c u l a t e d ) at T3.41 5 2  (C^)  and T3.78 (C^).  The carbomethoxy methyls  give r i s e "to a sharp, s i x proton s i n g l e t at x6.27. methyl i s seen as a narrow doublet at T8.19  The Cg v i n y l  (J=1.5HZ), w h i l e the  t e r t i a r y methyl i s c o r r e l a t e d w i t h a s i n g l e t at T8.86.  The  C^Q  methylenes give r i s e to a broad s i n g l e t at x8.03, w h i l e the hydroxyl hydrogen causes a s i n g l e t at T7.22, which disappears on deuterium oxide.  Figure 15 d i s p l a y s the nmr spectrum of 147 a f t e r  treatment w i t h  D 0.  Figure 15.  Spectrum of Enone A l c o h o l 147.  NMR  adding  o  - 73 The uv spectrum  of ene-dione  148 f e a t u r e s an enhanced  extinction  * coefficient  f o r i t s n - ir  absorption  (c 165) , c h a r a c t e r i s t i c of  a 6 , Y - u n s a t u r a t e d k e t o n e s u c h as i s p r e s e n t i n 148. 5 5  (KBr) shows a s t r i k i n g 5.58,  Figure  5.72,  16.  5.78  NMR  c a r b o n y l r e g i o n w i t h f o u r bands p o s i t i o n e d at  and 5.86u.  The nmr,  Spectrum of Ene-dione  c o n s i s t e n t w i t h s t r u c t u r e 148. the C-j v i n y l p r o t o n . T6.22 and 6.26,  The i r spectrum  The two  shown i n f i g u r e  16, i s a l s o  148.  A m u l t i p l e t a t T3.51 carbomethoxy  i s a s s i g n e d to  methyl s i g n a l s a r e seen a t  w h i l e the Cg v i n y l m e t h y l g i v e s r i s e to a d o u b l e t  (J=1.5Hz) a t T8.12, and the C  g  m e t h y l produces a s i n g l e t  a t x8.75.  The c h e m i c a l s h i f t s o f the C, exo and endo-protons a r e c a l c u l a t e d  52  - 74 to be T7.32 and T7.53, r e s p e c t i v e l y ; each features a double doublet w i t h the main coupling of 16Hz  due. to the geminal i n t e r a c t i o n .  Superimposed on the exo-proton doublet i s a coupling w i t h the methine (J=5Hz), w h i l e the endo doublet i s f u r t h e r s p l i t i n t o two doublets  (J=4Hz), again by the  proton.  The C ^ Q methylenes give  r i s e to doublets w i t h a geminal coupling of 14Hz.  Their p o s i t i o n s  are c a l c u l a t e d t o be T7.76 and T8.14. 5 2  Further evidence f o r s t r u c t u r e s 147 and 148 was obtained from an i n t e r e s t i n g and novel (at l e a s t f o r these systems) and thermal i n t e r r e l a t i o n s h i p , shown i n Scheme 24.  photochemical  Thus p h o t o l y s i s  of enone a l c o h o l 147 i n benzene gave good y i e l d s of 148, i n accord SCHEME 24.  w i t h the 20 Thermolysis  _19 conversion seen p r e v i o u s l y ( I n t r o d u c t i o n ) . of 148, on the other hand, at 185°,  l e d to 50% y i e l d  of 147, a r e s u l t not before obtained f o r t h i s s t r u c t u r e . so obtained was  The  147  i d e n t i c a l i n every respect'to an authentic sample.  None of the expected ene-dione 149 I n t r o d u c t i o n ) was  detected.  (cf. , _19 ^ 1_8 transformation,  - 75 -  o  149 E = C0 Me 2  A p o s s i b l e explanation f o r the thermal conversion of 148 to 147 i s shown i n Scheme 25.  Thus a keto-enol tautomerization between  SCHEME 25.  1,3  shift  147  148 -«- 150 i s p o s s i b l e due to the s t a b i l i z i n g e f f e c t (through hydrogen bonding of the enol proton) of the nearby ester carbonyl group.  A  -  thermal  [l,3] s h i f t  76 -  of the C^-C^  bond from carbon  atoms 3 to 5 then  b r i n g s the double bond i n t o c o n j u g a t i o n w i t h the and  g i v e s 147 d i r e c t l y .  and  C^. i n 148  Ene-diones  The  presence  c a r b o n y l group  of e s t e r s u b s t i t u e n t s a t  i s r e q u i r e d to b r i n g about t h i s t r a n s f o r m a t i o n .  1_3 and _19_, which possess  but which l a c k the n e c e s s a r y  the same r i n g system as  e s t e r groups,  are not  148,  thermally  transformed  to enone a l c o h o l p r o d u c t s .  Keto-enol  tautomerism  i s a r e a d i l y observed  number o f $ - k e t o e s t e r s , such as 1 5 1  6 8  I n t h i s case, nmr  151  e n o l form  152.  measurements  152  have shown t h a t at room temperature, its  phenomenon f o r a  Ene-dione 148  as much, as 7% of 151  i s not e x a c t l y analogous  however, as t h e r e a r e no a-protons  to  p r e s e n t on carbon atom 6.  n e c e s s i t a t e s the e n o l ' s b e i n g formed a t C^. p r o c e s s should be r e a s o n a b l e  exists  as  151, This  N e v e r t h e l e s s , such  a  i n view of the e s t a b l i s h e d i n t e r m e d i a c y  of an e n o l i n the f o r m a t i o n of compound 19_ (see I n t r o d u c t i o n ) , which possesses  the same r i n g s k e l e t o n as  P h o t o l y s i s of 100  148.  i n t e r t - b u t a n o l l e d to the f o r m a t i o n of  product  - 77 -  147 plus a mixture of s e v e r a l other products, the nmr spectrum of which i n d i c a t e d the r e s u l t of a hydrogen a b s t r a c t i o n process from a carbomethoxy methyl group.  This mixture was not i n v e s t i g a t e d  further.  The formation of products 147 and 148 on i r r a d i a t i o n of 100 i n benzene can be explained again by an i n i t i a l 3-hydrogen a b s t r a c t i o n by oxygen to g i v e the b i r a d i c a l species 153 (Scheme 26).  Bonding  SCHEME 26.  147  148  0  as i n d i c a t e d then leads to 147 d i r e c t l y and ( l i k e l y ) to enol 150 which subsequently ketonizes to give 148.  - 78 Once again, no product analogous to 5_4_ was detected system.  Further d i s c u s s i o n of the photochemistry of 9_8 - 100  w i l l be reserved  4.  i n this  f o r s e c t i o n V.  D i e l s - A l d e r Adducts of some Substituted jv-Benzoquinones w i t h Hexa-2,4-d iene. The process of photochemical 3-hydrogen a b s t r a c t i o n has been  shown to be a remarkably general one f o r D i e l s - A l d e r adducts of j3-benzoquinones and a c y c l i c - 1 , 3 - d i e n e s ? ' I n 3  25  f a c t , up to the present  time, only two examples had been found which d i d not react v i a t h i s pathway; on C  j c  namely adducts 4_2 and 5_1_. I n both cases, the 3-hydrogens  and C  8  Q  which were deemed " a c c e s s i b l e " (Scheme 10) to the O  R  42  R = Me  51  R = Ph  0  carbonyl oxygen had been replaced by s u b s t i t u e n t s , thus b l o c k i n g t h i s process (see I n t r o d u c t i o n ) .  I t therefore became of i n t e r e s t to study other compounds analogous to 4j2, i n which the 3-hydrogen a b s t r a c t i o n process was expected to be unfavorable,  i n order to see i f p o s s i b l y d i f f e r e n t product  s t r u c t u r e s could be obtained v i a a photochemical pathway. compounds 102 and 103 were i n i t i a l l y chosen.  To t h i s end,  I n a d d i t i o n to the  reasons given above, i t was a l s o p o s s i b l e that the s e r i e s of compounds  - 79 -  42,  103 and 102 would p r o v i d e some a d d i t i o n a l  i n f o r m a t i o n on t h e  e f f e c t o f . b r i d g e h e a d s u b s t i t u e n t s , and thus the study s e r v e d t o parallel  that o f the s i m i l a r  s e r i e s 98_, 99, .100. J u s t  102  outlined.  103  An a d d i t i o n a l bonus was p r o v i d e d when, on examining  reaction  c o n d i t i o n s f o r the s y n t h e s i s of 102, i t was found t h a t adduct C-/Co  d i a s t e r e o m e r o f 102, was a v a i l a b l e .  In t h i s  101, the  case the B-hydrogens  101 on C  and C  c  j  adduct  0  o  were i n t h e o r y " a c c e s s i b l e " ;  5_2, i n which t h e competing  thus 101 was analogous to  p r o c e s s e s o f hydrogen a b s t r a c t i o n  by oxygen and by carbon were o p e r a t i n g .  The p o s s i b i l i t y of a s i m i l a r  c o m p e t i t i o n i n t h e case o f 101 was not o v e r l o o k e d .  A.  D i e l s - A l d e r adducts o f Duroquinone w i t h t r a n s , t r a n s - h e x a 2,4-diene (101 and 102).  Both adducts  101 and 102 were s y n t h e s i z e d by s e a l e d tube t h e r m o l y s i s  of a m i x t u r e o f duroquinone  (154)^ t r a n s , t r a n s - 2 , 4 - h e x a d i e n e , and 9  -. 80 -  hydroquinone,  a few c r y s t a l s of which were added to i n h i b i t polymerization  of the diene.  I t was found that on heating t h i s mixture at 140°,  adduct 102 was the major compound obtained. temperature  R a i s i n g the r e a c t i o n  to 180° r e s u l t e d , i n a d d i t i o n to considerable t a r formation,  the formation of 101, w i t h only a t r a c e of 102 being observed. s y n t h e t i c r e s u l t s are summarized i n Scheme 27.  The  I n both cases, y i e l d s  SCHEME 27.  101 were very low (5 - 10%).  The stereochemistry of the C^/Cg methyl groups i n 101 and 1C2 was assigned on the b a s i s of two arguments: a)  the endo stereochemistry 102 was assigned to the product  formed a t low temperature  ( k i n e t i c product) s i n c e k i n e t i c c o n t r o l of 7 0  the D i e l s - A l d e r r e a c t i o n normally leads to endo addition.. The exo  - 81 -  stereochemistry 101 on the other hand was assigned to the high temperature (thermodynamic) product since thermodynamic c o n t r o l favors exo s t e r e o c h e m i s t r y  70  That 1Q1 i s the thermodynamically more  s t a b l e adduct was supported by the observation that 102, on heating to 180° i n a sealed tube, was transformed to 101, although extensive decomposition occurred and the y i e l d was t h e r e f o r e low. b)  the d i f f e r e n c e i n the chemical s h i f t s of the C /C C  Q  protons  o  J  i n 101 (T7.17) and i n 102 (T7.85), may be a t t r i b u t e d to the a n i s o t r o p i c d e s h i e l d i n g " e f f e c t of the adjacent c i s carbonyl groups i n the 5  case of 101. A s i m i l a r but l e s s pronounced e f f e c t was observed for the C /C methyls (T9.02) i n 102 r e l a t i v e to those i n 101 (T9.12). The J o c  0  nmr s p e c t r a of 101 and 102 are compared i n f i g u r e 17.  a.  P h o t o l y s i s of 2,3,4a$,53,83,8a3-Hexamethyl-4a,5,8,8atetrahydro-1,4-naphthoquinone  (101).  I r r a d i a t i o n of a benzene s o l u t i o n of 101 r e s u l t e d i n a r a p i d , smooth conversion to two photoproducts 155 and 156 i n the time independent r a t i o of 1:2, as shown i n equation 28. Column chromatography  (eq. 28)  155  1  156  :  2  - 82  Figure 17.  NMR  -  Spectra of Adducts 101 and  102.  -83 -  afforded 155 and 156 i n 25% and 56% y i e l d s , r e s p e c t i v e l y .  The  s t r u c t u r e s of the photoproducts were assigned on the b a s i s of t h e i r s p e c t r a l s i m i l a r i t i e s to the analogous compounds _53_ and 5 4  2 5  Enone a l c o h o l 155, a c o l o r l e s s c r y s t a l l i n e s o l i d , features hydroxyl (2.88y) and a,$-unsaturated carbonyl (6.05y) bands i n i t s i r spectrum.  Figure 18.  The nmr spectrum, shown i n f i g u r e 18 d i s p l a y s a s i n g l e  NMR Spectrum of Enone A l c o h o l 155.  v i n y l resonance a t T4.15 (Cg proton) and a s i n g l e t at T7.67 which disappears on adding deuterium oxide, i n d i c a t i n g i t i s due to the  -84  -  hydroxyl proton. V i n y l methyl s i g n a l s appear at T8.16 and T8.25 (2 m e t h y l s ) , w h i l e two t e r t i a r y methyls show s i n g l e t s at T9.20 and  9.34.  The C^Q methine appears as a broad m u l t i p l e t , centered at T7.79. The C^Q methyl group, coupled to the C^Q methine (J=7.5Hz) gives r i s e to a doublet at T9.29.  The s t r u c t u r e of ene-dione 156 was i n d i c a t e d by i t s i r spectrum, f e a t u r i n g two carbonyl bands at 5.66  (four-membered  and 5.85u (six-membered c y c l i c ketone). i s shown i n f i g u r e 1_9_.  Figure 19.  NMR  c y c l i c ketone)  The nmr spectrum of 154  A double doublet at T4.03  Spectrum of Ene-dione 156.  i s assigned to  - 85 the C „ v i n y l proton, coupled to the C C  7  /  methine (J=5.5Hz).  The C  n  v i n y l (J=10Hz) and to the  v i n y l s i g n a l at T4.49 shows a s p l i t t i n g 5z  9  of 1.5Hz, superimposed on the 10Hz coupling, which i s due to a l l y l i c coupling w i t h the i s assigned to the m u l t i p l e t at T7.82.  methine.  The quartet (J=7.5Hz) at T7.30  methine, w h i l e the  methine gives r i s e to a  Two doublets, each w i t h a s p l i t t i n g of 7.5Hz,  are found a t T8.98 and T9.02 due to the two methyls on C ^ a n d respectively.  I n a d d i t i o n , four other methyl s i n g l e t s are observed  at T8.98, 9.01, 9.03 and 9.09.  Spin-spin decoupling experiments v e r i f i e d the above assignments. Thus i r r a d i a t i n g the quartet at T7.30 causes the doublet at T8.98 to c o l l a p s e to a s i n g l e t .  I r r a d i a t i o n a t T7.S5 r e s u l t s i n the  s i m p l i f i c a t i o n of the v i n y l resonances to an AB type system, and to c o l l a p s e of the doublet at T9.02 to a s i n g l e t .  The stereochemistry a t C ^ Q i n 155, and at  and Cj i n 156,  i s assumed, based on the proposed mechanism f o r t h e i r formation. Support f o r the stereochemistry at  i n 156 was found i n the thermal  conversion of 156 to 157 (eq. 29). This r e a c t i o n p a r a l l e l s the  195°  (eq.  sealed tube 0  156  157  29)  - 86 54  _56 c o n v e r s i o n  25  (see I n t r o d u c t i o n ) and may  be c o n s i d e r e d as  an  example of a r e t r o - e n e r e a c t i o n ( a r r o w s ) , a l t h o u g h an a l t e r n a t e , 2 8  non-concerted of 157  mechanism cannot be r u l e d out a t p r e s e n t .  The s t r u c t u r e  f o l l o w s d i r e c t l y from i t s s p e c t r a l d a t a , which a r e r e p o r t e d  i n the e x p e r i m e n t a l those f o r compound  The  s e c t i o n , and which a r e found 56  to be s i m i l a r  to  2 3  c o m p e t i t i v e p r o c e s s e s of 3-hydrogen a b s t r a c t i o n by oxygen  and y-hydrogen a b s t r a c t i o n by enone carbon which form b i r a d i c a l i n t e r m e d i a t e s 158 account  and  159  (Scheme 28)  f o r the f o r m a t i o n of p r o d u c t s  r e s p e c t i v e l y , appear to 155  and  156.  Thus the  SCHEME 28.  156  photochemistry  - 87  of  101  i s analogous  b.  -  to t h a t observed f o r adduct  54.  P h o t o l y s i s of 2,3,4aB,5a,8a,8a3-Hexamethyl-4a,5,8,8atetrahydro-1,4-naphthoquinone  Irradiation  of 102,  (102) .  the course of the r e a c t i o n b e i n g f o l l o w e d by  g l p c , l e d t o the f o r m a t i o n o f two p r o d u c t s s u b s e q u e n t l y as the i n t r a m o l e c u l a r oxetane Glpc showed t h a t 160 was ratio  to 102 o f 1:1.9;  independent.  identified  160 and the cage compound 161  formed  r a p i d l y u n t i l i t reached a  t h e r e a f t e r , t h i s r a t i o was  Cage d i k e t o n e 161 was  (Scheme 29). relative  found to be  time  formed more s l o w l y , a t the  SCHEME 29.  0  .0  161  expense o f b o t h  160 and  102,  u n t i l i t remained  the s o l e p r o d u c t .  Workup of the r e a c t i o n thus, a l l o w e d f o r the i s o l a t i o n o f a q u a n t i t a t i v e  - 88  y i e l d of 161.  -  Small q u a n t i t i e s of oxetane 160 could be obtained  by p r e p a r a t i v e glpc i f the photoreaction was i n t e r r u p t e d before ->•  complete conversion to 161 had occurred.  The 102  160 e q u i l i b r i u m  was v e r i f i e d by photolyzing a sample of 160 i n benzene.  This p h o t o l y s i s  was monitored by g l p c , which showed a r a p i d formation of 102 u n t i l the 160:102 r a t i o reached a value of 1:1.9.  On prolonged p h o t o l y s i s  (12 hours) cage isomer 161 was again formed at the expense of both 102 and  160.  Both products were shown to be isomeric w i t h 102 by t h e i r mass spectra and elemental analyses.  Cage dione 161 was i s o l a t e d as a  c o l o r l e s s s o l i d whose s t r u c t u r e was i n d i c a t e d by i t s s p e c t r a l data. The i n f r a r e d spectrum features two carbonyl bands at 5.68 and 5.75y. S i m i l a r s p l i t carbonyl peaks have been observed °for the bridged 1  cage compounds 10 (n = 1,2).  O  10  n =  1,2  The nmr spectrum of 161 i s displayed i n f i g u r e 20, and  supports  the symmetrical s t r u c t u r e 161 i n that s e v e r a l sets of magnetically Thus, the two proton quartet at  equivalent protons are i n d i c a t e d .  T7.40 (J=7Hz) i s assigned to the C / C 7  in  methines, coupled to the  C /C 7  - 89 -  methyl groups;  these give r i s e to a doublet (J=7Hz) at T9.33.  Two  other sharp s i n g l e t s , each i n t e g r a t i n g f o r 6 protons, are present at T8.97 and x9.06, which account f o r the remaining methyl groups. The C  Q  and C  n  methines show a sharp s i n g l e t at T7.60.  any c o u p l i n g between the C /C and C / C g  g  7  1Q  The l a c k of  protons suggests  that t h e i r d i h e d r a l angle i s approximately 90°?° Examination.of a molecular model of 161 r e v e a l s t h i s to be the case.  Figure 20. NMR Spectrum of Cage-dione 161. The stereochemistry at C^/C^ i s assumed on the b a s i s of 1) the proposed mechanism and 2) the a l t e r n a t i v e symmetrical stereochemical arrangement of methyl groups at C /C^Q would be s t e r i c a l l y h i g h l y 7  unfavorable.  - 90  -  The s t r u c t u r e of 160 also r e s t s on i t s s p e c t r a l data.  The i r  spectrum (KBr) shows an a,B-unsaturated carbonyl s t r e t c h at 6.04y, but no hydroxyl band.  Figure 21.  The nmr of _1_60 shown i n f i g u r e 21, proved to  NMR Spectrum of Oxetane 160.  be most informative.  The proton s i t u a t e d at Cg shows a doublet  at T5.64, coupled to the C^ methine (J=4Hz) which appears at T7.40. Two quartets at T7.78 (J=7Hz) and T8.35 (J=7.5Hz) may be a t t r i b u t e d to the C, and C b y  Q  methines, i n t e r a c t i n g with the C, and C methyls, b y Q  which are assigned to doublets occurring at T9.01 (J=7Hz) and T9.46 (J=7.5Hz).  A molecular model of 160 reveals that the C, methyl o hydrogens may p o s s i b l y experience an a n i s o t r o p i c s h i e l d i n g e f f e c t  -  91  -  caused by the nearby carbonyl group "and 5  thus may give r i s e to the  doublet at higher ( T 9 . 4 6 ) f i e l d , although such an assignment can only be regarded as t e n t a t i v e .  Broad s i n g l e t s at T8.03 and  are a t t r i b u t e d to the  v i n y l methyls, r e s p e c t i v e l y ;  and  8.33 their  r e l a t i v e s h i f t s again r e f l e c t the p o l a r i z a t i o n i n the unsaturated carbonyl chromophore and the r e s u l t i n g d e s h i e l d i n g e f f e c t at the atom. Sharp s i n g l e t s at T8.97 and 9.30  are assigned to the methyls  s i t u a t e d at C , . and C ^ Q , r e s p e c t i v e l y .  Again, the stereochemistry  at C , / C „ i s assumed to be that shown, on the b a s i s of the proposed 6  9  mechanism.  The photochemistry of 102 thus departs from that of k2 (see I n t r o d u c t i o n ) i n that no product was observed, the formation of which could be accounted f o r by a hydrogen a b s t r a c t i o n process ( c f . , the 42 ->• 4_4 conversion). A process such as that encountered i n the case of adduct 42 would have given r i s e to compound 163, v i a b i r a d i c a l 162  (eq.  31). H»C  OH  hv Y~H  abstraction  (eq. 31)  by oxygen 102  163  (not formed)  Instead, photoproducts 160 and 161 are observed, both formally the r e s u l t of intramolecular Jjr2 + 7T2 1 c y c l o a d d i t i o n s i n v o l v i n g g  - 92 -  the  remote double bond and e i t h e r a carbonyl group (oxetane 160  formation) or the ene-dione double bond (cage product 161 formation). Both processes are i n theory o r b i t a l symmetry allowed\ although 8  they are r a r e l y , i f ever, a c t u a l l y o b s e r v e d ?  1 - 7 3  The divergent photochemistry of 102 again suggests that a conformational e f f e c t has been introduced i n t o the system by the presence of the bridgehead methyl groups i n 102. presence of s t r u c t u r e  On t h i s b a s i s , the  164 ( i e . t w i s t conformer C, Scheme 10)  i s suggested, which may i n turn suggest two s i m i l a r mechanisms leading to the formation of oxetane 160.  These are shown i n Scheme 30.  164 Path A involves i n i t i a l overlap of proximate p_-orbitals on carbons C. and C, (164) , r e s u l t i n g i n b i r a d i c a l intermediate 165 1 o which can c o l l a p s e d i r e c t l y to 160.  Path 3, on the other hand, t  involves i n i t i a l overlap of the p - o r b i t a l s on oxygen and carbon C  7  to give b i r a d i c a l 167, which subsequently c o l l a p s e s to oxetane 160.  SCHEME*  30.  167  I t should be pointed out that path A represents an unusual mechanistic route to oxetane formation.  Path B, on the other hand,  i s modelled a f t e r the f a m i l i a r Paterno-Buchi r e a c t i o n * i n which 71  an e x c i t e d carbonyl compound undergoes r e a c t i o n w i t h an o l e f i n , r e s u l t i n g i n the formation of oxetanes v i a a b i r a d i c a l intermediate' ( f i g u r e 22).  «  1  - 94 -  A Figure 22.  +  Paterno-Buchi Reaction.  However, i t i s u n l i k e l y that path B i s the mechanism which accounts f o r the formation of 160, because b i r a d i c a l 167 v i o l a t e s Bredt's r u l e .  The to 161,  t w i s t conformer 164 i s also the l i k e l y s t r u c t u r a l precrusor since the only v i a b l e a l t e r n a t i v e , s t r u c t u r e 168, would  be disfavored  by bridgehead methyl e c l i p s i n g .  The  slower rate of  168  formation of 161 r e l a t i v e to f a s t e r 102 be due  to e i t h e r a)  160 e q u i l i b r i u m may  i n fact  the much smaller amount of p r e r e q u i s i t e conformer  168 present at e q u i l i b r i u m compared to t w i s t conformer 164; the remoteness of the double bonds i n t w i s t conformer  164.  or  b)  - 95 I t i s conceivable that cage product 161 could a r i s e v i a Path A (Scheme 30) through a j l , 3 ] . s u p r a f a c i a l sigmatropic s h i f t of the C^ - C bond, which would give b i r a d i c a l 166. Closure then between carbons 2 and 8 would r e s u l t i n the formation of 161. Such a rearrangement i s unusual, however, and to the best of the author's knowledge, unprecedented.  In a d d i t i o n to these c o n s i d e r a t i o n s , the p o s s i b i l i t y of i n i t i a l excited molecular complex, or e x c i p l e x formation should be considered. In the past decade, a great deal of evidence has been presented supporting the contention that the i n i t i a l i n t e r a c t i o n between an excited s t a t e molecule and a ground s t a t e molecule i s often the formation of an e x c i p l e x (excited molecular complex)? of  5  I n the case  102, the e x c i p l e x formation would be i n t r a m o l e c u l a r , w i t h an  excited ene-dione chromophore i n t e r a c t i n g w i t h the i s o l a t e d double bond;  t h i s then would c o l l a p s e , p o s s i b l y t o products 160 and 161  d i r e c t l y o r , more l i k e l y , to b i r a d i c a l intermediate 165. No evidence for of  such e x c i p l e x formation was observed i n the u l t r a v i o l e t 102. However, as many s t u d i e s have shown lack 76  spectrum  of ground s t a t e  i n t e r a c t i o n does not n e c e s s a r i l y mean that i n t e r a c t i o n does not occur i n the e x c i t e d s t a t e .  The photochemistry of 102 thus proved unique f o r the s e r i e s of  ]  - 96 -  D i e l s - A l d e r adducts studied i n our laboratory.  Indeed, the formation  of cage dione 161 represented the f i r s t known example of cage isomer formation f o r a D i e l s - A l d e r adduct l a c k i n g a C (cf. I n t r o d u c t i o n ) .  r  - C„ bridge or bond  Thus the p o t e n t i a l a v a i l a b i l i t y of other  s t r u c t u r a l l y s i m i l a r compounds l e d to an i n v e s t i g a t i o n of the dicyano adduct 103.  B.  v  4aB,8a3-Dicyano-5a,8a-dimethyl-4a,5,8,8a-tetrahydro-1,4naphthoquinone (103).  Adduct 103 was synthesized i n a manner analogous to 9J3, as shown i n Scheme 31. SCHEME 31.  135  103  P h o t o l y s i s of 103 i n e i t h e r benzene or t e r t - b u t a n o l r e s u l t e d i n the formation of a s i n g l e photoproduct, i d e n t i f i e d to be oxetane 169 by i t s s p e c t r a l data chromatography.  and i s o l a t e d i n 50 - 60% y i e l d a f t e r column  - 97 Product 169 e x h i b i t s a 5.93y band i n the i r spectrum, c h a r a c t e r i s t i c of the unsaturated carbonyl group.  The nmr spectrum of 169, l i k e  that of the analogous oxetane 160, was p a r t i c u l a r l y informative, and i s reproduced i n f i g u r e 23.  ^  '  !  1  •  i  1  \  1  i  1  '  1  i  1  1  ' '  1  I  ''  The C  ''  i '  •'  and  9  i  1  •'• i  v i n y l protons show  '  r-r'-'—r  L  Figure 23.  NMR Spectrum of Oxetane 169.  an AB system, located at constant of 10Hz.  T2.46  and T3.73, r e s p e c t i v e l y , with a coupling  A doublet at T5.23 (J=4Hz) i s due to the Cg  methine; coupled to the C^ methine, i t s e l f also a doublet, located at T6.83.  As was the case w i t h oxetane 160, approximate 90° d i h e d r a l  angles f o r the C  n  - C  D  hydrogens, as w e l l as f o r the C, - C, hydrogens,  account f o r the l a c k of coupling i n e i t h e r case.  The C  fi  and C  Q  methines  - 98 -  show sharp quartets at T7.11 and T7.35, w i t h coupling constants of 7 and 7.5Hz, r e s p e c t i v e l y .  The C, and C_ methyl resonances (each 6  9  a doublet) are located at T8.60 (J=7Hz) and a t T9.05 (J=7.5Hz).  Once  again, the u p f i e l d doublet i s t e n t a t i v e l y assigned to the C, b  methyl by v i r t u e of a n i s o t r o p i c s h i e l d i n g by the nearby carbonyl.  Double resonance experiments a l s o v e r i f i e d the above assignments. Thus i r r a d i a t i o n at T9.05 l e d to c o l l a p s e of the T7.35 quartet to a singlet;  i r r a d i a t i o n at T5.23 r e s u l t e d i n the c o l l a p s e of the T6.83  doublet to a s i n g l e t ;  i r r a d i a t i o n at T3.73 caused the doublet at  T2.46 to c o l l a p s e to a s i n g l e t .  Ultimate support f o r s t r u c t u r e 169 was obtained by an x-rav c r y s t a l s t r u c t u r e determination, which v e r i f i e d that s t r u c t u r e 169 i s indeed c o r r e c t and the Cg/C stereochemistry i s as shown. y  The  s i m i l a r i t i e s i n the nmr spectra of 169 ( f i g u r e 23) and 160 ( f i g u r e 21), coupled w i t h the x-ray r e s u l t s , a l s o lends credence to the s t r u c t u r e proposed f o r 160. The author would l i k e to thank Dr. J . T r o t t e r and Dr. S. P h i l l i p s f o r the x-ray determination.  U n l i k e oxetane 160, compound 169 was found to be i n e r t to prolonged p h o t o l y s i s i n e i t h e r benzene or t e r t - b u t a n o l , even when i r r a d i a t e d w i t h l i g h t f i l t e r e d through Pyrex ( t r a n s m i t t i n g X > 290 nm).  - 99 None of the cage isomer 170, analogous to 161, was ever observed.  170 Furthermore, no products a r i s i n g from a. hydrogen a b s t r a c t i o n process could be detected.  The formation of 169 from 103 very l i k e l y p a r a l l e l s the formation of 160 from 102, discussed p r e v i o u s l y (Scheme 30) i n terms of i n i t i a l overlap of proximate p_-orbitals on carbon atoms 1 and 6. the  Again,  p o s s i b i l i t y of i n t r a m o l e c u l a r e x c i p l e x formation should not be  ignored.  5.  Discussion The formation of photoproduct 5_4 from adduct 5_2 marked a  t u r n i n g point i n the photochemistry of D i e l s - A l d e r adducts of s u b s t i t u t e d jv-benzoquinones w i t h acyclic-1,3-dienes.  P r i o r to t h i s  novel r e s u l t , the products derived from D i e l s - A l d e r adducts were n i c e l y explained on the b a s i s of the mechanism i n v o l v i n g 6-hydrogen a b s t r a c t i o n by carbonyl oxygen. the  To e x p l a i n the divergent nature of  photochemistry of _5_2, two a l t e r n a t i v e s seemed l i k e l y :  - 100 1)  The presence of methyl s u b s t i t u e n t s on the ene-dione  chromophore a l t e r s the energies of the e l e c t r o n i c (presumably t r i p l e t ) * excited s t a t e s , making the TT - TT s t a t e lower i n energy than the * n — TT (cf. , the B a r l t r o p suggestion, I n t r o d u c t i o n ) . The formation * * of _54_ thus o r i g i n a t e s from a TT - TT s t a t e , rather than an n — TT s t a t e , the l a t t e r accounting f o r the formation of JJ$ - ^0 o n p h o t o l y s i s of _17_, and analogous products from analogous adducts l a c k i n g ene-dione double bond s u b s t i t u e n t s . 2)  The presence of bridgehead methyl s u b s t i t u e n t s favors  a twisted conformer i n the ground s t a t e (conformer C, Scheme 10), which i n turn f a c i l i t a t e s the process of y-hydrogen a b s t r a c t i o n by enone carbon which i s the l i k e l y mechanism of formation of 54.  The r e s u l t s presented i n t h i s t h e s i s d i s f a v o r the f i r s t of the two proposals presented above.  Adducts 9_5 and 9_6, each w i t h one  substituent on the ene-dione double bond, d i s p l a y a r e g i o s e l e c t i v e product d i s t r i b u t i o n , i n much the same manner as adduct 36_, on i r r a d i a t i o n , i n l i n e w i t h the expected r e l a t i v e s t a b i l i t i e s of the proposed b i r a d i c a l intermediates. 95 and  However, n e i t h e r the mono adducts  nor adduct 9_7, w i t h two methyl substituents on the ene-dione  double bond, give r i s e to products which can reasonably be a t t r i b u t e d to a process other than 3-hydrogen a b s t r a c t i o n by carbonyl oxygen. In the case of 9_7, the chromophore i s i d e n t i c a l to that present i n adduct 52.  - 101  -  Thus the second f a c t o r came to be.considered;  namely, that  the photochemical r e a c t i o n was under the i n f l u e n c e of ground s t a t e conformational c o n t r o l .  An e v e r - i n c r e a s i n g number of l i t e r a t u r e reports have been appearing r e c e n t l y i n which the photochemical r e a c t i o n s observed r e f l e c t the i n f l u e n c e of ground s t a t e conformation on e x c i t e d s t a t e behaviour. Baldwin and K r u e g e r p r o v i d e d an e a r l y example when they studied 77  the photochemistry of a-phellandrene (171).  I r r a d i a t i o n of 171 l e d  to two primary photoproducts 172 and 174, which suffered secondary p h o t o l y s i s to give 173 and 175 (eq. 33).  The appearance of 172 and  (eq.  ;-CH,  174  i.C H 3  T  33)  175  174 corresponds to the two p o s s i b l e conrotatory e l e c t r o c y c l i c r e a c t i o n s p o s s i b l e f o r 171, and the authors became i n t e r e s t e d i n the p o s s i b i l i t y that these two conrotatory modes were r e l a t e d to the two p r i n c i p l e conformational isomers of 171 ( i e . 171e, where the isopropy group  - 102 -  i s p s e u d o e q u a t o r i a l , and 171a, where i t i s a x i a l ) . that  i f the p h o t o i s o m e r i z a t i o n o f conformers  They  reasoned  171a and 17le was  h i g h l y s t e r e o s e l e c t i v e , g i v i n g r i s e t o the product a n t i c i p a t e d examining  a model emphasizing  determinant,  then the r a t i o  from  ground s t a t e geometry as a s t e r e o c h e m i c a l  of p r o d u c t s 174/172 should be a  q u a n t i t a t i v e measure o f the e q u i l i b r i u m c o n s t a n t K =  171e/171a  (Scheme 32). SCHEME 32.  hv  hv  174  172 The of  e q u i l i b r i u m c o n s t a n t K c o u l d be determined  through a study  the o r d and cd s p e c t r a of 171 as a f u n c t i o n o f temperature.  temperature  dependence o f p r o d u c t r a t i o  174/172 was then  The  determined  and was found t o be c o n s i s t e n t w i t h t h e p o s t u l a t e d s t e r e o s e l e c t i v i t y i n the c o n v e r s i o n s 171a  172 and 171e + 174.  Thus, they c o n c l u d e d  the s t e r e o c h e m i s t r y o f a common type o f v a l e n c e i s o m e r i z a t i o n was c o n t r o l l e d by conformer  p o p u l a t i o n i n the r e a c t a n t .  that  - 103 Lewis and co-workers have provided another example of conformational ;8  c o n t r o l of photoproduct formation. They noted the r e s u l t s reported by Baldwin, but observed that the chromophore i n 171 i s part of the conformationally mobile system, and thus the energy b a r r i e r s to conformational i s o m e r i z a t i o n i n the ground s t a t e and excited s t a t e need not be the same.  The simplest s i t u a t i o n f o r studying conformational e f f e c t s i n photochemistry occurs when two conformers A and B of a substrate give r i s e to d i f f e r e n t photoproducts (X and Y, r e s p e c t i v e l y ) . summarized i n Scheme 33. Two l i m i t i n g cases are p o s s i b l e .  This i s In case I ,  SCHEME 33. hv  hv  the that  -> A  *  * •B  A  k  B  *" X  >Y  a c t i v a t i o n energy f o r conformational i s o m e r i z a t i o n i s lower than f o r formation of X or Y ( k ^ * »  k^.kg).  I n t h i s case the  r a t i o of products w i l l depend upon the d i f f e r e n c e i n energy of the t r a n s i t i o n s t a t e s leading to X and Y ( C u r t i s - Hammett p r i n c i p l e  7 9 3  ),  and the l i f e t i m e s of both excited s t a t e conformers w i l l be the same. In case I I , the a c t i v a t i o n energy f o r conformational i s o m e r i z a t i o n  -  is greater  than that  104 -  f o r formation  o f X o r Y (k^g*  t h i s c a s e , the r a t i o o f p r o d u c t s w i l l A  and B  <  <  k^,kg).  e l e c t r o n i c e x c i t a t i o n i s much f a s t e r than n u c l e a r 0 0  ),  the i n i t i a l  populations  determined by ground s t a t e p o p u l a t i o n s their respective  n  depend on the p o p u l a t i o n of  and t h e i r e f f i c i e n c i e s of product f o r m a t i o n .  Condon P r i n c i p l e  -*-  And s i n c e  motion  of A  (Franck -  and B  w i l l be  of conformers A and B and.  extinction coefficients.  Here t h e i r l i f e t i m e s need  not be the same.  The  systems chosen f o r study c o n s i s t e d o f some c y c l o h e x y l -  p h e n y l ketones 176 - 178 and c y c l o p e n t y l p h e n y l  ketone 179.  The w e l l  known a - c l e a v a g e and y-hydrogen a b s t r a c t i o n r e a c t i o n s o f phenyl a l k y l ketones effects.  (eq. 34 and 35) were used as probes f o r c o n f o r m a t i o n a l  As t h e chromophore i n each case i s n o t a p a r t o f t h e  c y c l o a l k y l r i n g , conformational fairly  straightforward  little  i f any p e r t u r b i n g  a n a l y s i s was a n t i c i p a t e d to be  s i n c e e l e c t r o n i c e x c i t a t i o n should e f f e c t on t h e c o n f o r m a t i o n a l  process.  0  0  R^C  = CH  2  have v e r y  isomerization  - 105 The r e s u l t s of t h i s study are presented i n Scheme 34, which shows the observed photoproducts a r i s i n g from ketones 176 - 179. Table V l i s t s  ———  v  corresponding quantum y i e l d data f o r the formation  of benzaldehyde ($^) and b i c y c l o b u t a n o l  , and corresponding rate  constants (k ,k ) f o r these processes as determined a y quenching techniques. SCHEME 34.  183  by Stern-Volmer  - 106 TABLE V.  Quantum Y i e l d s and K i n e t i c Data f o r C y c l o a l k y l Phenyl Ketones.  Ketone •  Solvent  176  Ph + RSH  177  Ph  178  Ph + RSH  0.31  179  Ph + RSH  0.03  The  <J> _a  $ _y_  0.20  0.045  k  ( s e c ')  2.5 x 1 0  2.1 x 1 0  ?  1.3 x 1 0  7  0.19  8  6.9 x 1 0  8  1.3 x 1 0  ?  177 and 178 s e r v e as f i x e d models  f o r the two p o s s i b l e  c o n f o r m a t i o n a l isomers of 176.  formed by p h o t o l y s i s  o f 177 and 178 were those o f y-hydrogen  (182) and a - c l e a v a g e  (sec y  1.7 x 1 0  7  0.09  tert-butyl derivatives  abstraction  k  J  a  The p r o d u c t s  (181) r e s p e c t i v e l y .  The absence o f  an a - c l e a v a g e product from 177 was c o n s i d e r e d t o r e f l e c t the considerably  f a s t e r r a t e c o n s t a n t f o r y-hydrogen a b s t r a c t i o n ,  whereas  the l a c k o f y-hydrogen a b s t r a c t i o n p r o d u c t s from 178 was a t t r i b u t e d to t h e l a r g e 0 - H  distance. Y  The  p h o t o c h e m i s t r y o f 176 was then d e s c r i b e d ,  on t h e b a s i s  of the  r e s u l t s f o r 177 and 178, i n terms of t h e r e l a t i v e p o p u l a t i o n s o f conformers 176a ( b e n z o y l group a x i a l ) and 176e (benzoyl group e q u a t o r i a l ) , as.shown i n Scheme 35. to 180 w h i l e 176e r e s u l t e d I t was known (AG  +  7  i n a - c l e a v a g e t o g i v e benzaldehyde 181. fl  that  A x i a l conformer 176a l e d  _  the a c t i v a t i o n energy f o r c y c l o h e x y l  = 9.9 k c a l mole  -1  ) was much l a r g e r than t h a t  chair  inversion  f o r y-hydrogen  - 107 -  SCHEME 35.  176a  180  a b s t r a c t i o n from valerophenone (184 - E  approx. 3.5 k c a l mole  );  The a c t i v a t i o n energv f o r a-cleavage had not been measured, but was  184 reasoned to be l e s s than 10 k c a l mole reasoned  that conformers 176a and 176e  . On t h i s b a s i s then, i t was should react more r a p i d l y  than i n v e r t (k * << k ,k ). This p r e d i c t i o n was born out by the ae a y markedly d i f f e r e n t slopes of the Stern - Volmer p l o t s  f o r quenching  of b i c y c l o b u t a n o l and benzaldehyde formation and the subsequently derived r a t e constants f o r these processes (Table V). From t h i s i t followed that product $'s should depend upon conformational populations,  - 108 -  and e f f i c i e n c y of product formation from the e x c i t e d s t a t e conformers. A f t e r c o r r e c t i n g f o r the observed somewhat greater absorption of the 78  a x i a l vs e q u a t o r i a l model compounds 177 and 178, an e x c i t e d s t a t e population of 176a was determined  to be 35% and of 176e, 65%.  The quantum y i e l d f o r benzaldehyde formation ( $ ) from 176e was a  found to be e x a c t l y 65% of the value f o r the model compound 178. Thus the r e s u l t s f o r compound 176 were i n accord w i t h the hypothesis that conformational populations i n f l u e n c e product quantum y i e l d s , and compound 176 belongs to case I I .  In contrast to the above, the energy b a r r i e r f o r cyclopentane pseudorotation i s considerably smaller than that f o r cyclohexane r i n g i n v e r s i o n ^ t h u s the authors f e l t that the pseudorotation i n 79  179 might compete e f f i c i e n t l y w i t h a-cleavage and y-hydrogen abstraction.  This was born out by the i d e n t i c a l Stern - Volmer s l o p e s  f o r quenching of benzaldehyde and b i c y c l o b u t a n o l formation from 179 (and thus the i d e n t i c a l r a t e constants f o r these processes - Table V). This r e s u l t e x a c t l y p a r a l l e l s the s i t u a t i o n observed *for both 8  a c y c l i c ketones 185 and 186, where the Stern - Volmer p l o t s f o r quenching of benzaldehyde and cyclobutanol formation have i d e n t i c a l  185  186  7  - 109 slopes i n each instance.  Here, the energy b a r r i e r f o r r o t a t i o n about  a s i n g l e bond (3.5 - 4.5 k c a l mole * ) l s known to be comparable 8  to that f o r y-hydrogen a b s t r a c t i o n ?  3  Thus the r e s u l t s observed f o r photoreaction of 179 are consistent w i t h case I , where the r a t e of conformational  i s o m e r i z a t i o n competes,  e f f e c t i v e l y w i t h the r a t e s of chemical r e a c t i o n .  Here product  composition depends upon the r e l a t i v e rates of formation of products and not upon conformational  One  populations.  example of apparent ground s t a t e conformational  has been observed  control  p r e v i o u s l y i n our l a b o r a t o r y , i n the photochemistry  of adduct 187, shown i n Scheme 36.  The formation of 188 as the sole  SCHEME 36.  187  188  190  189  -  110  -  product on i r r a d i a t i o n  of 187 was  187  should be formed p r e f e r e n t i a l l y .  suggested  s t r u c t u r e 188  t h a t 189  s u r p r i s i n g , as m o l e c u l a r models of  f o r the photoproduct  was  determined  However,  unambiguously  by  x-ray c r y s t a l l o g r a p h y .  The  f o r m a t i o n of 188 was  analysis.  r a t i o n a l i z e d on the b a s i s of c o n f o r m a t i o n a l  Of the f i v e conformers  c o u l d account  f o r the  These are 190 and  191  p o s s i b l e i n Scheme 10, o n l y  J2 + 2J c y c l o a d d i t i o n observed  likely  s t e p w i s e > i t was 7 3  which would g i v e 189,  As the f o r m a t i o n of  reasoned  8  i n t e r m e d i a t e 192 which g i v e s 188 193,  i n the case of  (Scheme 36), i n which the e x o c y c l i c v i n y l  i s c l o s e to the ene-dione double bond. was  two  due  on c l o s u r e , was  e x p e r i e n c e d d u r i n g i t s f o r m a t i o n , such as the the C  group  product  t h a t the f o r m a t i o n of b i r a d i c a l f a v o r e d over t h a t of  to the l e s s e r non-bonded  i n t e r a c t i o n i n conformer 190 and  c  interactions  carbonyl-vinyl  a x i a l hydrogen-vinyl  interaction  o i n conformer 191. preferred  Thus, i t was  reasoned  t h a t the v i n y l  to r o t a t e so as to occupy the " o u t e r " or exo  which l e a d s to 192  as opposed to the more congested  p o s i t i o n which would a f f o r d  192  187.  group position  8 4  " i n n e r " or endo  193.  193  The p h o t o i s o m e r i z a t i o n of c y c l o b u t y l p h e n y l ketone 194  to the  -  Ill  -  SCHEME 37. Y-H  abstraction  Ph  arrows  194e + OH  195  i n i t i a l l y discussed  Ph  O Ph'  CH CH CH=CH 2  2  2  196  i n terms of ground s t a t e conformational  control!*  The r e a c t i o n i s characterized by a very low quantum e f f i c i e n c y ($) and a very slow rate of Y~hydrogen a b s t r a c t i o n (Ky) r e l a t i v e to other a l k y l phenyl ketones.  These data are summarized i n Table V I .  The slow r a t e was a t t r i b u t e d to the low concentration of the r e a c t i v e q u a s i - a x i a l isomer 194a; k  t h i s was confirmed by the higher observed  f o r compound 199, a r i g i d model f o r conformer 194a.  The low  quantum y i e l d i n the case of 199 was a t t r i b u t e d to a r a p i d t r i p l e t ft fi  d e a c t i v a t i o n mechanism, that of hydrogen back t r a n s f e r .  However,  the r e a c t i v i t y ( i e . k ) of 199 was now s i m i l a r to that of valerophenone (184), which implied then that the low r e a c t i v i t y observed f o r 194  - 112 -  TABLE  VI.  $ arid  of some Phenyl A l k y l Ketones. k (sec _L_  Ketone  PK  1  0.03  5.5 x 10"  0.40  6.7 x 10  0.49  8.3 x 10  0.44  8 1.3 x 10  0.06  3.9 x 10  0.20  4.1 x 10'  194  0 PK  197  184  8  199  0  200  Ph  - 113 -  ( i e . k ) was due to the low concentration Y  of r e a c t i v e conformer 194a. '  Alexander then s t u d i e d a s e r i e s of j J - s u b s t i t u t e d a r y l - c y c l o b u t y l 87  ketones 201, and found that the quantum y i e l d f o r r e a c t i o n of ketones 201 changed d r a m a t i c a l l y i n much the same way as observed of other phenyl a l k y l k e t o n e s a s the e l e c t r o n withdrawing power of the substituent 88  increased  (as shown i n Table VII).  TABLE VII. Quantum Y i e l d Dependence of Reaction of A r y l - c y c l o b u t y l Ketones on p-Substituent (x).  p-CH .  0.001  p-F  0.050  3  p-CF  3  0.089  ^1  X = CH ,F,CF 3  3  Three p o s s i b l e mechanisms were c o n s i d e r e d t o account f o r the 87  low concentration  of the r e a c t i v e a x i a l conformer ( c f . 194a), and  therefore low quantum y i e l d of r e a c t i o n of ketone 194; 1)  namely  c o n t r o l by ground state conformational e q u i l i b r i u m , 2)  by r i n g i n v e r s i o n i n the excited s t a t e , 3) conformational e q u i l i b r i u m .  control  c o n t r o l by excited  state  Alexander determined that these three 87  mechanisms were d i s t i n g u i s h a b l e by k i n e t i c a n a l y s i s .  From the  quantum y i e l d data (Table VII) f o r the r e a c t i o n of ketone 201, the t h i r d mechanism, namely c o n t r o l by e x c i t e d s t a t e conformational e q u i l i b r i u m , was i n d i c a t e d .  - 114 Conformational e f f e c t s on the behavior of b i r a d i c a l have a l s o been demonstrated i n the l i t e r a t u r e . r e i n v e s t i g a t e d the photochemistry  intermediates  Agosta and S c h r e i b e r  of cyclohexanone 202 which had  p r e v i o u s l y been s h o w n ' t o y i e l d unsaturated aldehyde 203 90  89  38  and  ketene 204 (trapped as the methyl e s t e r ) . They focused t h e i r a t t e n t i o n on the stereochemistry of the hydrogen t r a n s f e r from C^ or C^ to C^ i n the -reaction leading to 203 (Scheme 38) and considered  two  possibilities: SCHEME 38.  205 a)  the transformation could be s t e r e o s p e c i f i c , w i t h e i t h e r the  a x i a l or e q u a t o r i a l hydrogen s e l e c t i v e l y migrating to the carbonyl carbon ( s t r u c t u r e 205); b)  or  the o r i g i n a l d i s t i n c t i o n between a x i a l and e q u a t o r i a l  hydrogen at C^ or C,. i s l o s t before the hydrogen t r a n s f e r occurs. The compounds chosen to c l a r i f y the nature of the rearrangement were the deuterated methyl cyclohexanones 206-208.  P h o t o l y s i s of 206 and  207  - 115 led to corresponding aldehyde 209 (eq. 36), and i r r a d i a t i o n of 208  gave 210 predominantly, plus a l i t t l e 211 (eq. 37). of 209 and 210 the deuterium l a b e l l i n g at  In the instances  and C,. was  determined  O  206 207  208  210 by nmr spectroscopy.  211  The data obtained f o r the l a b e l l i n g i s recorded i n  Table V I I I . TASLE V I I I .  L a b e l l i n g paterns of deuterated 209 and  Compound and P o s i t i o n  210.  % Protium  C  x  of 209 from 206  85  C  5  of 209 from 206  72  C  x  of 209 from 207  C  5  of 209 from 207  29  C  x  of 210  65  C  c  of 210  37  '  '  18  - 116 From these data, the percentages of a x i a l hydrogen t r a n s f e r were c a l c u l a t e d , as reproduced i n Table IX.  TABLE IX. Percentage A x i a l H - t r a n s f e r , ketone -*• aldehyde. 206 + 209  207  209  208 -> 210  Based on C  1  64  63  68  Based on C  5  74  64  68  From these r e s u l t s , the authors concluded that there i s very l i t t l e s p e c i f i c i t y i n the r e a c t i o n of 202 (approximately 2/3 of the aldehyde protons came from the a x i a l p o s i t i o n w h i l e 1/3 o r i g i n a t e d from the e q u a t o r i a l ) and postulated the intermediacy of a b i r a d i c a l such as 212 w i t h a l i f e t i m e s u f f i c i e n t to permit f r e e r o t a t i o n about the  - C,. bond leading to the c h a i r l i k e intermediates 213  and 214.  The observed preference f o r a x i a l m i g r a t i o n could then be i n t e r p r e t e d i n terms of 213, i n which the methylene group i s e q u a t o r i a l , being e n e r g e t i c a l l y favored over 214, where i t i s a x i a l .  - 117 A second study by Agosta and Wolff ^ o f the more r i g i d b i c y c l o [3.2.1] octan-6-one (215) system a l s o demonstrated  conformational  e f f e c t s on the behavior of b i r a d i c a l intermediates.  P h o t o l y s i s of  215 r e s u l t s i n a-cleavage to give the a x i a l b i r a d i c a l 216a (Scheme 39). I t had been shown that c y c l o h e x y l r a d i c a l s behave conformationally 92  l i k e cyclohexane or cyclohexanone.  R a d i c a l 216a can then s u f f e r a  second hydrogen t r a n s f e r from the side chain to the r i n g to give ketene 217, or.from the r i n g to the s i d e chain to give aldehyde 218. I f 216a i n v e r t s to the e q u a t o r i a l conformer 216e, then only aldehyde 218 i s p o s s i b l e .  A f i n a l p o s s i b i l i t y i s the presence of boat  SCHEME 39. CHjCHO  216b  - 118 conformer 216b, which would give r i s e to aldehyde 219 by hydrogen t r a n s f e r from r i n g to side chain.  As i n s u f f i c i e n t q u a n t i t a t i v e information was a v a i l a b l e to r e l i a b l y p r e d i c t the conformational behavior of 216, several s u b s t i t u t e d bicyclo-octanones of known stereochemistry were i n v e s t i g a t e d t o 91  determine the r o l e of conformational c o n t r o l on the behavior of the biradical.  Agosta's r e s u l t s are reproduced i n Table X.  ,  The data presented i n Table X give an e x c e l l e n t c o r r e l a t i o n between the' f a t e of the b i r a d i c a l 216 and expected conformational e f f e c t s i n the six-membered r i n g .  Ketones 220 and 221, f o r which  the a x i a l conformer 216a i s the s t a b l e one, y i e l d ketene and v i r t u a l l y no aldehyde.  For ketones 222 - 224, where conformer 216e  i s c l e a r l y more s t a b l e , e s s e n t i a l l y the sole product observed i s the corresponding aldehyde.  For ketone 225, i n which both conformers  216a and 216e should be r e l a t i v e l y equal i n energy and hence concentration, a product mixture of aldehyde and ketene i s observed.  In no instance  was the boat conformer 216b detected ( v i a aldehydes 219).  From these r e s u l t s , A g o s t a concluded that conformational 91  e q u i l i b r i u m shown i n Scheme 39 must be considered i n the r e a c t i o n of 215, and that d i s p r o p o r t i o n a t i o n of the b i r a d i c a l intermediate 216  - 119 -  TABLE X. Products of P h o t o l y s i s of B i c y c l o [3.2. l] oetan-6-ones.  Substrate  Methyl Ester (from ketene)  Aldehyde  < 0.5% 96%  220  CH CO Me 1  l  < 4% 75%  221 CH CHO t  222  < 0.5%  93% CHTCHO  223  < 2%  85% CH CHO T  H.CO O  OCK  224  85%  s  < 0.5%  CH,CO,M«  225  44%  54%  - 120 occurs from the stable cyclohexane c h a i r conformer i n each instance.  Returning now to the photochemistry of D i e l s - A l d e r adducts of £-benzoquinones with a c y c l i c dienes, the i n f l u e n c e of conformational c o n t r o l on product formation appears to be implicated by the r e s u l t s presented here and p r e v i o u s l y .  The i n i t i a l case to be considered i s conformational c o n t r o l in the ground s t a t e ;  i e . the presence of bridgehead substituents  in  adducts 52 and j)8_ - 103 favoring a twisted conformation, such as conformer C (Scheme 10, I n t r o d u c t i o n ) , which leads to the unusual products observed, such as 54_ (from 52) , 156 (from 101), 160 and 161 (from 102) and 169 (from 103). are reproduced i n Scheme 40. SCHEME 40.  For convenience, these transformations  - 121 The absence of bridgehead substituents (other than hydrogen) then permits the molecule to assume one or more of the other p o s s i b l e conformers (Scheme 1 0 ) , and thus gives r i s e to products w i t h s t r u c t u r e s t y p i f i e d by those found i n products 1_8 - ^ 0 (eq. 38).  To gain i n f o r m a t i o n on t h i s p o i n t , x-ray s t r u c t u r e determinations were c a r r i e d out on a number of the adducts studied both p r i o r to and i n t h i s work.  Figure 24 shows computer drawn stereodiagrams of  adducts JJO, _52, _97, 9_8 and 1 0 1 . At t h i s point the author wishes to acknowledge and thank Drs. J.R. T r o t t e r and S. P h i l l i p s f o r t h e i r x-ray s t r u c t u r e determinations and h e l p f u l d i s c u s s i o n s .  The d e t a i l e d  r e s u l t s of t h e i r work i s being published, separately.  On examination of f i g u r e 2 4 , one f a c t i s immediately obvious: a l l adducts assume the twisted conformation, depicted i n f i g u r e 25, i n the s o l i d s t a t e , regardless of bridgehead s u b s t i t u t i o n .  Therefore, 9 3  very l i k e l y , the twisted conformer i s predominant i n s o l u t i o n as w e l l , although others are a l s o p o s s i b l e depending on the b a r r i e r conformational isomerism.  to  - 122 -  Figure 25. Table XI l i s t s p e r t i n e n t 0-H and C_-H o  J  P  Y  contact distances f o r  .the adducts shown i n f i g u r e 25, along w i t h the d i h e d r a l angles a and 3, as defined i n f i g u r e 25. These data were determined i n the course of the x-ray s t r u c t u r e determinations, and serve to show the very s i m i l a r nature of the s o l i d s t a t e conformation of each adduct. I t TABLE XI Compound  0-H (X)*  c -H (£)  10  2.49(3)  2.96(3)  63(2)  68.9(2)  52  2.47(6)  2.89(6)  60^0(6)  61.4(5)  97  2.42(6)  3.09(6)  56(3) .  71.4(4)  98  2.58(3)  2.92(3)  60.9(2)  64.0(2)  101  2.26(3)  2.70(3)  62.6(3)  60.7(3)  3  g  y  +  a(  )  3(°)  *  i n Figure 24 these are the C^-H -+ 0^ d i s t a n c e s , except f o r 52,  t  where i t i s the C,-H*0„ d i s t a n c e . o I i n Figure 24 these are the C,-H->C„ d i s t a n c e s , except f o r 5_2, where 6  i t i s C„-H-»-C d i s t a n c e . 0  .i.  - 123 Figure 24.  Adduct 10.  Stereodiagrams of D i e l s - A l d e r Adducts.  0(1)  0(1)  0(2)  0(2)  Adduct 52.  CU2)  C112)  Adduct 97.  can  can  0(21  C18)£  Adduct 101.  IC(14)  - 125 seems then that while small conformational d i f f e r e n c e s are i n adducts w i t h bridgehead  s u b s t i t u e n t s (52, 98, 101)  observed  relative  to those w i t h hydrogen (10, 97), the ground s t a t e conformational argument cannot completely e x p l a i n the d i f f e r e n t  photochemistry  observed f o r adducts w i t h bridgehead s u b s t i t u e n t s .  An examination of molecular models of these D i e l s - A l d e r adducts, b i r a d i c a l intermediates and f i n a l products reveals an important f a c t . In order f o r the b i r a d i c a l formed by the process of 6-hydrogen a b s t r a c t i o n to c o l l a p s e to an ene-dione photoproduct ( c f . Scheme 5, 21 —  18 + 19), a conformational r o t a t i o n about the C, - C_ bond — — 4a 8a  i s required to s i t u a t e the p_-orbitals of the b i s - a l l y l i c system such that bonding may  occur.  This i s i l l u s t r a t e d i n Figure 26.  A b s t r a c t i o n of the B-nydrogen by e x c i t e d carbonyl oxygen gives s t r u c t u r e 226 ( i e . b i r a d i c a l 21).  The formation of 18 then requires a r o t a t i o n about the C, - C„ — 4a 8a M  bond (represented by the 226 •+ 227 transformation) to b r i n g the £-orbitals on  and Cg o f the b i s - a l l y l i c system i n t o proximity.  For the formation of J_9, the b i r a d i c a l must assume s t r u c t u r e 228, where the bridgehead  s u b s t i t u e n t s ( i e . hydrogens) are nearly e c l i p s e d ,  to favorably s i t u a t e the p - o r b i t a l s on C^ and C  fi  f o r bonding.  -126 -  Figure 26. However, the formation of an enone a l c o h o l photoproduct  from the  b i r a d i c a l ( c f . 21 •*• 2Q, Scheme V) r e q u i r e s no, or very l i t t l e , conformation change p r i o r to bond formation.  The jp_-orbitals on  - 127 carbon atoms C, and C  of the b i s - a l l y l i c system ( s t r u c t u r e 226)  are already favorably s i t u a t e d f o r bonding to occur.  Figure 27 shows by means of computer drawn stereodiagrams t h i s conformational s i m i l a r i t y of enone a l c o h o l photoproduct to substrate (the D i e l s - A l d e r adduct) f o r the s p e c i f i c case of adduct 98_ and product 136.  Figure 27.  - 128 Models r e v e a l a s i m i l a r s i t u a t i o n to be true f o r formation of 54 from 52 (and 156 from 101) namely bonding between C„ and C„ requires very l i t t l e conformational change i n the b i r a d i c a l intermediate. The s i t u a t i o n f o r adducts 54 and K)_l can thus be summarized i n Figure 28.  230 Figure 28. Thus, the formation of enone a l c o h o l photoproducts  ( l i k e 53  and 155 and of the ene-dione products 54 and 156 r e q u i r e s very l i t t l e conformational change to undergo 1,6 or 2,8 bonding, r e s p e c t i v e l y ,  ne£  - 129 -  from t h e i r r e s p e c t i v e b i r a d i c a l i n t e r m e d i a t e s .  These c o n s i d e r a t i o n s thus suggest t h a t t h e p h o t o c h e m i s t r y o f D i e l s - A l d e r adducts o f p_-benzoquinones thus f a r s t u d i e d i s c o n t r o l l e d  and a c y c l i c  1,3-dienes  i n p a r t by c o n f o r m a t i o n a l e f f e c t s  on t h e b i r a d i c a l i n t e r m e d i a t e s i n v o l v e d .  I n m o l e c u l e s where a  3-hydrogen a b s t r a c t i o n p r o c e s s i s p o s s i b l e , t h e p r e s e n c e o f b r i d g e head s u b s t i t u e n t s p r o h i b i t s a c o n f o r m a t i o n a l r o t a t i o n about t h e C. - C bond by r a i s i n g t h e energy b a r r i e r f o r such a r o t a t i o n , 4a oa Q  and  thus p h o t o p r o d u c t s w i t h t h e s t r u c t u r e s found i n 18.  a n <  a r e not o b s e r v e d .  Only enone a l c o h o l  some c a s e s , ene-dione  * 12.  ( c f . s t r u c t u r e 20) and, i n  o f s t r u c t u r e 54_ a r e observed, b o t h o f which  p o s s e s s the same r e l a t i v e c o n f o r m a t i o n s as t h e i r r e s p e c t i v e b i r a d i c a l intermediates  The  (and s t a r t i n g D i e l s - A l d e r a d d u c t s ) .  e f f e c t o f b r i d g e h e a d s u b s t i t u e n t s on t h e energy  to c o n f o r m a t i o n a l r o t a t i o n i n t h e c l o s e l y r e l a t e d system  (231  9 1  T h e i r d a t a a r e reproduced  i n Table XII, along w i t h data f o r c i s - d e c a l i n 4a-methyl-cis-decalin Roberts?  cis-decalin  232) has been measured u s i n g nmr t e c h n i q u e s by Altman,  et a l * f o r a s e r i e s o f s u b s t i t u e n t s .  and  barrier  (231, R=H), and  (231, R=H, R'=Me), as determined by G e r i g  5  231  132  -  TABLE X I I .  Energy  130 -  t e r r i e r s t o I n v e r s i o n f o r Some C ^ - Cg^  Disubstituted  cis-decalins.  E —a  R, R' = H  a p p r o x i m a t e l y 14  R = H, R' = Me  a p p r o x i m a t e l y 10  R, R' = C H C 0 C H  20.6  ± 0.6  R, R' = CH Br  18.7  ± 1.2  R = B r , R' = CN  18.3  ± 0.9  2  2  3  2  A s i g n i f i c a n t i n c r e a s e i n t h e energy inversion  i n cis-decalin  decalin  6  An apparent found  likely  t h e energy b a r r i e r s  system,  to i n v e r s i o n o f  affected.  e x c e p t i o n t o t h e above c o n f o r m a t i o n a l arguments i s  i n t h e f o r m a t i o n o f ene-dione  hV  100  ring  substitution.  somewhat s m a l l e r than those f o r the c i s -  system , may be s i m i l a r l y 9  to conformational  tetrahydronaphthoquinone  i s reasonable to suspect that  conformation,although  barrier  i s thus i n t r o d u c e d by b r i d g e h e a d  For t h e r e l a t i v e l y s i m i l a r it  ( k c a l mole  S  Compound  E = C0 Me 2  148 on i r r a d i a t i o n o f adduct 100.  - 131 Compound 148 i s the only photoproduct  of t h i s type observed thus f a r  where the bridgehead p o s i t i o n s which are nearly e c l i p s e d are occupied by a s u b s t i t u e n t other than hydrogen.  A l l that can be s a i d here i s  that the energy b a r r i e r to conformational i s o m e r i z a t i o n of the b i r a d i c a l i s s u f f i c i e n t l y l e s s f o r carbomethoxy s u b s t i t u e n t s , r e l a t i v e to methyl s u b s t i t u e n t s , to permit the formation of 148 to occur. complete conformational r o t a t i o n about the C^ - C &  g a  Clearly, a  bond i n the b i r a d i c a l  i s an unfavorable process, as ene-dione 149, the formation of which requires such a conformational change, i s not observed.  A d d i t i o n a l i n s i g h t i n t o the photochemistry of tetrahydronaphthoquinones has been obtained from the work of Scheffer and Louwerens, who r e c e n t l y s t u d i e d t h e Stern-Volmer 98  quenching k i n e t i c s f o r  adducts 52 and 1_7. For the case of 52, i t was found that the formation of ene-dione 54_ can be quenched be adding cyclohexa-1,3-diene to the photoreaction mixture, w h i l e the formation of enone a l c o h o l _53 i s u n a f f e c t e d , suggesting that products _53 and 54 o r i g i n a t e from s i n g l e t and t r i p l e t e x c i t e d s t a t e s r e s p e c t i v e l y . precedent f o r these observations.  There i s l i t e r a t u r e  Recently, A g o s t a p u b l i s h e d some 99  data r e l e v a n t to the r e a c t i o n s l i s t e d i n Scheme 13 ( i n t r o d u c t i o n ) .  - 132 -  He  found t h a t  leading  the p r o c e s s e s of 3-hydrogen a b s t r a c t i o n by oxygen,  to c y c l o p r o p a n e p r o d u c t s , and y-hydrogen  a b s t r a c t i o n by  oxygen, g i v i n g c y c l o b u t a n e p r o d u c t s (Scheme 1 3 ) , were b o t h o r i g i n a t i n g from the s i n g l e t  e x c i t e d s t a t e , as n e i t h e r p r o c e s s was  p r e s e n c e o f quencher.  S i m i l a r l y , the p r o c e s s o f hydrogen  by enone c a r b o n has been shown by s e v e r a l workers a triplet  The  excited  a f f e c t e d by the  '  abstraction to  involve  state.  case o f adduct _ 1 7 , i n which  3-hydrogen a b s t r a c t i o n by  oxygen i s the o n l y p r o c e s s g i v i n g r i s e to p r o d u c t s i s a l s o i n l i n e w i t h t h e above.  A l l the p r o d u c t s J J ? -  2MD (Scheme 4 ) were found  to o r i g i n a t e from the s i n g l e t e x c i t e d s t a t e , a l t h o u g h f o r the p r o d u c t s formed  i n benzene (namely _19 and 2 0 ) , a t r i p l e t  state reaction i s also  and  excited  indicated.  The f a c t t h a t o n l y two of the adducts s t u d i e d 52  two  1 0 1 ) r e a c t v i a a y-hydrogen  thus f a r  (namely  a b s t r a c t i o n by carbon mechanism  m e r i t s some d i s c u s s i o n a t t h i s p o i n t .  The r e s u l t s o b t a i n e d f o r  those a d d u c t s i n which a 3-hydrogen a b s t r a c t i o n by oxygen p r o c e s s i s p o s s i b l e can be summarized by Scheme -41.  It triplet  appears t h a t i n t e r s y s t e m c r o s s i n g  (a) from the s i n g l e t  to  e x c i t e d s t a t e i s not an e f f i c i e n t p r o c e s s i n the p h o t o c h e m i s t r y  of t e t r a h y d r o n a p h t h o q u i n o n e s ;  rather,  3-hydrogen a b s t r a c t i o n  (k„)  - 133  SCHEME  -  41.  (53,  155,  20)  ene-diones (^8 and  19)  occurs to generate a b i r a d i c a l intermediate.  In those cases where  the b i r a d i c a l contains bridgehead hydrogens, conformational i s o m e r i z a t i o n (k ) competes w i t h formation of enone a l c o h o l ( k , , ) , and w i t h c lp r e v e r s i o n to ground s t a t e a d d u c t  1 0 0  ( k ) and r e s u l t s i n the formation D  "P  of ene-dione photoproducts such as 28 and 19.  On the other hand, the presence of bridgehead s u b s t i t u e n t s , as i n adducts _52 and 1 0 1 , makes conformational changes i n the b i r a d i c a l l e s s l i k e l y (k  «  k  1 A  and k„).  Thus, formation of enone a l c o h o l and  -  134  -  r e v e r s i o n to ground s t a t e adduct  are the only r e a c t i o n pathways  a v a i l a b l e to the b i r a d i c a l derived from the excited s i n g l e t s t a t e . This should i n turn allow f o r an ever i n c r e a s i n g f r a c t i o n of s i n g l e t excited s t a t e s to undergo intersystem crossing and subsequently s u f f e r y-hydrogen a b s t r a c t i o n to give product 54_ or  156.  This -explanation f i n d s some support i n the solvent dependence observed f o r the product d i s t r i b u t i o n i n the case of adduct 52. 86 '  I t i s known that the hydrogen atom back t r a n s f e r mechanism f o r the N o r r i s h I I r e a c t i o n can be made l e s s important by conducting the r e a c t i o n i n solvents of i n c r e a s i n g p o l a r i t y .  This a l s o seems to  be the case f o r adduct _52_ (see Scheme 11) - i n c r e a s i n g r e l a t i v e amounts of enone a l c o h o l 53_ are formed at the expense of 54_ as the solvent p o l a r i t y i s increased. In the cases of adducts 9_8_ - 100, where i t i s a l s o i n d i c a t e d that k  c  «  k,, and k (Scheme 41), reason f o r the f a c t that no 1,6 -8 0  compound analogous to _54 i s observed i s not obvious.  One  possible  explanation i s that the absence of methyl substituents on carbon atoms  and  i n j)8 - 100 make the process of hydrogen a b s t r a c t i o n  by carbon unfavorable, owing to the l e s s e r s t a b i l i t y of the b i r a d i c a l intermediate which would be formed, namely 233, r e l a t i v e to that of ^0 (cf. Scheme X I I ) .  ' .  Another p o s s i b l e explanation analogous to the proposals of Barltrop * and Schaf f n e r (cf. Introduction) i s that i n the case of * 1  7  38  54 (and hence 101) , intersystem c r o s s i n g gives r i s e to a TI — TT t r i p l e t state-(due to the presence of the  and  methyl groups)  which leads to hydrogen a b s t r a c t i o n by enone carbon. compounds l a c k i n g methyl substituents on  and  For those  (10, 17, 98,  99, 100) intersystem c r o s s i n g occurs to a t r i p l e t n - TT s t a t e * which, l i k e the (presumably) n - TT s i n g l e t s t a t e , reacts v i a the process of 3-hydrogen a b s t r a c t i o n by oxygen.  Some support f o r t h i s  l a t t e r explanation i s found i n the work of Louwerens where 98  p h o t o l y s i s of adduct _17_ i n benzene was found to give r i s e to JL9_ and 20 from both the s i n g l e t and t r i p l e t excited s t a t e s . A comparison of the photochemistry of adducts 102 and 103 suggests a c o n t r i b u t i o n by ene-dione methyl s u b s t i t u e n t s , i n l i n e w i t h those proposed above, f o r these substrates as w e l l .  While both  102 and 103 give r i s e to oxetane photoproducts, adduct 102 eventually reacts q u a n t i t a t i v e l y to give cage compound 161, the formal r e s u l t of a c y c l o a d d i t i o n r e a c t i o n between the i s o l a t e d double bond and the s u b s t i t u t e d ene-dione double bond.  I n the case of 103, where the  ene-dione double bond i s unsubstituted, no corresponding cage  - 136  -  isomer 170 i s observed.  A conformational  c o n t r o l argument can also account f o r the  observed d i f f e r e n c e i n the photochemistry of adducts 102 and 103, from that of 4_2_.  Again models r e v e a l that b i r a d i c a l 4_5 (Scheme 9) ,  formed by y-hydrogen a b s t r a c t i o n by oxygen from the nearby methyl group i n 42_, ( s t r u c t u r e 234), must undergo a conformational (as shown by the 235 -*• 236 transformation  rotation  i n f i g u r e 29) to b r i n g the  e x o c y c l i c methylene r a d i c a l i n t o p o s i t i o n f o r bonding to carbon atom 3. Figure 29.  For compounds 102  and  137  103,  such c o n f o r m a t i o n a l r o t a t i o n i s  a g a i n p r e v e n t e d by the presence of bridgehead s u b s t i t u e n t s . w h i l e hydrogen  a b s t r a c t i o n from the methyl by oxygen may  Thus  be a ready  p r o c e s s , the b i r a d i c a l so d e r i v e d i s c o n f o r m a t i o n a l l y immobile d u r i n g the b i r a d i c a l l i f e t i m e and s u b s e q u e n t l y d e a c t i v a t e s b a c k 8 6  to s t a r t i n g m a t e r i a l . to 102 and (160 and  Thus the o n l y p h o t o c h e m i c a l pathway  available  103 l e a d i n g to p r o d u c t s appears to be oxetane f o r m a t i o n  169,  respectively).  A g a i n the c o n f o r m a t i o n of the  i s v e r y s i m i l a r to t h a t of i t s p r e c u r s o r , as shown i n f i g u r e where the c o n f o r m a t i o n s of adduct  103 and oxetane  While the n e t change i n • c o n f o r m a t i o n i n the 103  oxetane 30,  169 a r e compared. 169 t r a n s f o r m a t i o n  appears to be g r e a t e r than t h a t f o r the s i m i l a r 9J3 ->• 136 t r a n s f o r m a t i o n , ( f i g u r e 28) no r o t a t i o n about ° r e q u i r e d t o form 169  from  the s u b s t i t u t e d C. - C„ bond i s 4a 8a  103.  Another p o s s i b l e p r o c e s s a v a i l a b l e to 102 and to be a b s t r a c t i o n of a methyl hydrogen S t r u c t u r e 234  103 would  appear  by an enone carbon atom.  ( f i g u r e 29) shows t h a t such a p r o c e s s i s c e r t a i n l y  p o s s i b l e i n t h a t the methyl H - carbon c o n t a c t can be as l i t t l e 2.91  X  (as determined by x - r a y a n a l y s i s ) .  biradical which  i n t h i s case  (eq. 39,  seems t o be a requirement  ( c f . compound _70,  Introduction).  as  However, the d e r i v e d  237) would l a c k resonance  stabilization  f o r s u c c e s s of t h e s e r e a c t i o n s  - 138 -  Figure  30.  Adduct  103.  Oxetane 169.  -  139  -  (eq. 39)  102  R=R'=Me  103  R=H, R'=CN  A f i n a l point to be noted  237  i s the emergence of new product  s t r u c t u r e s from the p h o t o l y s i s of adducts 102 and 103.  I t has been  p r e v i o u s l y n o t e d t h a t p h o t o l y s i s of D i e l s - A l d e r adducts _17 and j42 25  o f f e r s ready entry i n t o the r i n g systems found i n c e r t a i n n a t u r a l products.  I t may thus be suggested that p h o t o l y s i s of tetrahydro-  naphthoquinone r i n g systems which are s u b s t i t u t e d a p p r o p r i a t e l y can give r i s e to yet other novel, and p o t e n t i a l l y u s e f u l compounds and r i n g systems through the i n f l u e n c e of conformational introduced i n t o the system by those s u b s t i t u e n t s .  effects  The formation of  oxetanes 160 and 169, and cage dione 161 r e a d i l y a t t e s t to t h i s proposal.  I t may a l s o be stated that f o r many, i f not a l l , of the D i e l s Alder adducts synthesized i n our l a b o r a t o r y , the stereochemistry was completely  unknown i n i t i a l l y .  However, the photoreactions  adducts c e r t a i n l y e s t a b l i s h t h e i r stereochemistry,  of these  and i t i s a n t i c i p a t e d  that these r e a c t i o n s may be s i m i l a r l y used f o r other adducts.  -  140  -  EXPERIMENTAL General Procedures I n f r a r e d ( i r ) spectra were recorded on a Perkin-Elmer 137 spectrophotometer i n one of three ways:  a) from neat l i q u i d samples  between sodium c h l o r i d e p l a t e s , b) using KBr p e l l e t s containing 0.5% by weight of sample, and c) as 5% chloroform or carbon t e t r a c h l o r i d e solutions.  Nuclear magnetic resonance (nmr) spectra were recorded  by the departmental nmr s e r v i c e on the f o l l o w i n g instruments: Model A-60, T-60, HA-100 and XL-100 spectrophotometers; t e t r a m e t h y l s i l a n e was used as the i n t e r n a l standard.  Varian  i n a l l cases,  Mass spectra  were obtained on A t l a s CH-4-B and AEI-MS-902 spectrometers, and u l t r a v i o l e t (uv) spectra were recorded on a Unicam Model SP 800 B spectrophotometer, using methanol as solvent unless otherwise i n d i c a t e d . Microanalyses were performed by Mr. P. Borda of t h i s  department.  M e l t i n g p o i n t s were determined on a Fisher-Johns melting point apparatus and are uncorrected, unless otherwise s p e c i f i e d .  Gas l i q u i d p a r t i t i o n  chromatography was c a r r i e d out on Varian Aerograph Model 90-P Varian Aerograph Autoprep Model A 700 chromatographs;  and  both were  connected to Honeywell E l e c t r o n i k 15 s t r i p chart recorders.  The  - 141 -  c a r r i e r gas was helium i n a l l cases.. The f o l l o w i n g columns were employed:  20% DEGS, 5' x h" (column A);  10% 0V-1, 7' x V  (column C).  10% FFAP, 5' x V  (column. B ) ;  I n the t e x t , the column w i l l be given,  followed by the column oven temperature and c a r r i e r gas flow r a t e i n parentheses. For column chromatography, S i l i c a Gel ( p a r t i c l e s i z e l e s s than 0.08 mm) from E. Merck AG was employed, and was packed as a s l u r r y i n the e l u t i n g solvent;  packing and e l u t i o n were  c a r r i e d out under 5-10 p s i nitrogen pressure.  Alumina used was  Woelm, n e u t r a l , a c t i v i t y grade I . Thin-layer chromatography ( t i c ) was performed on pre-coated aluminum f o i l t i c sheets obtained from E. Merck AG, e i t h e r Aluminum Oxide F-254 n e u t r a l (type T) or S i l i c a Gel  60 F-254.  I n both cases, the l a y e r thickness was 0.2 mm.  Unless  otherwise i n d i c a t e d , photolyses were performed by means of a 450 W medium pressure Hanovia type L lamp placed i n a water cooled quartz immersion w e l l .  Interposed between the lamp and r e a c t i o n v e s s e l  was a 15 x 15 cm p l a t e of Corning #7380 glass ( t r a n s m i t t i n g l i g h t of X >_ 340 nm), which was cooled by a stream of a i r . v e s s e l was 6 - 1 0 inches from the lamp.  The r e a c t i o n  Solutions to be i r r a d i a t e d  were f i r s t degassed f o r at l e a s t h hour w i t h Canadian L i q u i d A i r argon.  A l l solvents used were reagent grade and were d i s t i l l e d  p r i o r to use.  - 142  -  4a8,5,8,8a3-tetrahydro-2,6,7-trimethyl-l,4-naphthoquinone  (95).  This m a t e r i a l was prepared by the method of Bergmann and Bergmann!* A s l u r r y of 2 g (0.016 mole) of methyl-_p_-benzoquinone 9  (Eastman, p r a c t i c a l ) , 3.5 g (0.043 mole) of butadiene and 0.01  2,3-dimethyl-l,3-  g of hydroquinone was placed i n a sealed Pyrex  tube and heated f o r 1 hour at 110°.  The now pale yellow r e a c t i o n  mixture, which s o l i d i f i e d upon c o o l i n g to a pale yellow s o l i d , was r e c r y s t a l l i z e d from methanol to give 2.52 mp 89-91° ( l i t ! * 9 3 - 94°).  Distinguishing spectral characteristics  9  were as f o l l o w s : 3.53  (m, 1,  7.5 - 8.0  i r (KBr) 5.98  (C=0) , 6.15  v i n y l ) , 6.7 - 7.0  (m, 4, C  c  and C  g (77%) of 95,  Q  (m, 2, C^^ and C  methylenes),  8.03  methyl), 8.37  5 o (br s, 6, C, and C, methyls);  long shoulder  (e at 340 = 130).  6  (C=C)u;  /  ga  nmr  (CCl^T  methines),  (d, 3, J=1.5Hz, C_ 2.  uv max  (methanol)  P h o t o l y s i s of Adduct 95_ i n Benzene. A s o l u t i o n of 804 mg  (3.94 mmoles) of 95_ i n 250 ml of benzene  was i r r a d i a t e d w i t h l i g h t of wavelength _> 340 nm. monitored by glpc (column A, 175°, buildup of 4 new products; the r a t i o of products was  The r e a c t i o n was  160 ml/min) which showed a r a p i d  a f t e r 6.5 hours, a l l _95_ had reacted, and 106:107:108:109 = 3.8:1:2.6:3.4 as determined  by c u t t i n g out and weighing peaks from the glpc chart paper.  Isolation  of the products was achieved by preparative glpc (same column and c o n d i t i o n s as above).  A l l were c o l l e c t e d as c o l o r l e s s o i l s which  - 143 crystallized  on standing, and were characterized by the f o l l o w i n g  properties: for 106_, 5-hydroxy-3,8,9-trimethyltricyclo [4.4.0.0 ' ] deca-3,75  diene-2-one:  colorless solid, recrystallized  mp 90 - 91.5°; 3.61  (m, 1,  from petroleum ether (68 ),  i r (CC1 ) 2.78 (OH), 5.93 (C=0)y; (m, 1, C  ?  o  Q  (m, l ,  8.22  methyls), 8.6 (m, 2, G.. methylenes), 8.91 lu  uv max  4  v i n y l ) , 7.05  7.6 - 7.9 (m, 1, C, methine), 7.70 ( s , 1, OH) C  nmr ( C C 1 ) T  4  v i n y l ) , 4.43  9  methine),  (br s, 6, C, and  ( s , 3, C. methyl); y  (methanol) 244 (e 6200), 325 nm (e 58);  mass spectrum (70 eV)  m/e parent 204. Anal. H,  Calcd.. f o r C-.H-.O.: C, 76.44; ij  7.79.  lo  H, 7.90.  Found:  C, 76.25;  2  3 7 f o r 107, 3 , 8 , 9 - t r i m e t h y l t r i c y c l o 4.4.0.0 ' dec-8-ene-2,5-dione: colorless solid, recrystallized i r (CCI.) 5.70 4  (C=0)y;  from petroleum ether (68°), mp 69 - 70°;  nmr (CC1.)T 7.40 4  (m, 1, C  7.65  (m, 2 ) , 7.65 - 7.8 (m, 2 ) , 7.79  8.01  (d, 1, J=18Hz, C^ endo-methylene), 8.28  8.38  (br s, 3, C  g  or C  g  methyl), 8.84  (methanol) 286 nm (e 78); Anal. 76.15;  H,  o  7.92.  6  methine), 7.5 -  (dd, 1, J=18Hz, 1Hz, C^ exo-methylene), (br s, 3, C  ( s , 3, C  3  g  or  methyl),  methyl); uv max  mass spectrum (70 eV) m/e parent 204.  Calcd. f o r C._H..0 : IJ  r  lo  2  C, 76.44;  H, 7.90.  Found:  C,  - 144 for 108, 3 , 8 , 9 - t r i m e t h y l t r i c y c l o J4.4.0.0 '^J  dec-7-ene-2,5-dione:  3  colorless solid, recrystallized 109.5°;  from petroleum ether (68°), mp 108.5 -  i r (CC1 ) 5.68 and 5.80 (C=0)y;  nmr ( C C 1 ) T 4.42 (br d, 1,  J=7Hz, C, v i n y l ) , 6.77 (dd, 1, J , ,=7Hz, / o, /  =8Hz, C, methine), 7.14 6,1 b  4  4  (d, 1, J=17.5Hz, C, exo-methine), 7.35 ( d t , 1, J . ,=8Hz, J . . =2Hz, 1,  4  o  1 ,  1 U  C. methine), 8.12 (d, 3, J=1.5Hz, C„ methyl), 8.15 (d, 1, J=17.5Hz, 1 o endo-methylene),  8.3 - 8.7 (m, 2, C^Q methylenes), 8.73 ( s , 3, Cg  methyl), 9.02 ( s , 3, C nm (e 426); Anal.  3  methyl);  uv max (methanol) 294 (e 481), sh 307  mass spectrum (70 eV) m/e parent 204. Calcd. f o r C H.,0„:  C, 76.44;  lo  H, 7.90.  Found:  C, 76.53;  H, 7.85.  f o r 109, 5-hydroxy-4,8,9-trimethyltricyclo [4.4.0.0 ' ] deca-3,7-diene5  2-one:  colorless solid, recrystallized  mp 92.5 - 93°;  9  from petroleum ether (68 ) ,  i r (CCl^) 2.80 (OH), 5.93 (C=0)y;  nmr ( C C l ^ T 4.29  (m, 1, C„ v i n y l ) , 4.36 (m, 1, C-, v i n y l ) , 7.00 (d, 1, J=3Hz, C, methine), 3 / o 7.51 ( s , 1, OH), 7.83 (m, 1,  methine), 8.06 (d, 3, J=1.5Hz,  methyl), 8.20 (d, 3, J=1.5Hz, C  Q  methyl), 8.47 and 8.52 (each a  o  s i n g l e t , ' 2, C^Q methylenes), 8.86 ( s , 3,  methyl);  uv max  (methanol)  244 (e 6100), a long t a i l i n g shoulder from 310 - 355 nm (e at 325 nm 51);  mass spectrum (70 eV) m/e parent 204. Anal.  76.23;  Calcd.  H, 7.77.  f o r C H.,0„: 1o  13 16 i.  C, 76.44;  H, 7.90.  Found:  C,  - 145 P h o t o l y s i s of Adduct 95 i n t e r t - B u t a n o l . A s o l u t i o n of 500 mg (2.45 mmoles) of 95 i n 200 ml of 10% (v/v) benzene/tert-butanol was i r r a d i a t e d w i t h l i g h t of wavelength >^ 340 nm.  The r e a c t i o n was monitored by glpc (column A, 175°,  160 ml/min) which showed the r a p i d buildup of 4 products a t the expense of _95.  Three of these products proved to be i d e n t i c a l t o  products 106, 107, and 109, obtained from the p h o t o l y s i s of 9_5 i n benzene.  Compound 108 wasn't formed;  was observed.  rather a new product 110  A f t e r 17 hours of i r r a d i a t i o n , the r a t i o of products  was 106:107:109:110 = 1:9.6:3:1, as determined by weighing the glpc peaks.  The four products were s u c c e s s f u l l y i s o l a t e d by p r e p a r a t i v e  glpc (same conditions as above).  Products 106, 107 and 109 were  i d e n t i f i e d by comparison of t h e i r s p e c t r a l p r o p e r t i e s w i t h those of the benzene p h o t o l y s i s products.  Product 110 was a l s o a c o l o r l e s s  s o l i d , r e c r y s t a l l i z e d from petroleum ether (68°), mp 78 - 79°, and 3 71  T  was i d e n t i f i e d as 4,8,9-trimethyltricyclo[4.4.0.0 ' Jdec-8-ene-2,5dione on the b a s i s of these s p e c t r a l p r o p e r t i e s : (C=0)y; (m, 1, C  nmr (CDCl^x 6.9 - 7.1 (m, 1, C £  3  i r (KBr) 5.72  methylene), 7.2 - 7.3  methylene), 7.4 - 7.6 (m, 2 ) , 7.6 - 7.8 (m, 3 ) , 8.27 (br s,  o 3, Cg or C  9  methyl), 8.39 (br s, 3, C  J=7.5Hz, C^ methyl);  g  or C  g  methyl), 8.95 (d, 3,  uv max (methanol) 283 nm (e 78); mass spectrum  (7Q eV) m/e parent 204. Anal. Calcd. f o r C^H^O-: lo l o 76.23; H, 7.82.  C, 76.44;  H, 7.90.  Found:  C,  - 146 Base Catalyzed Deuterium Exchange of Ene-Dione 107. To a s o l u t i o n of 15 mg (0.073 mmol) ene-dione 107 i n 0.5 ml deuterochloroform i n an nmr tube was added 5 drops of a 2N s o l u t i o n of KOH i n D^O. The tube was p e r i o d i c a l l y shaken f o r one day, a f t e r which time the nmr spectrum showed the complete disappearance of the s i g n a l due to the C^ exo-proton at T 7.79. The doublet due to the endo-proton collapsed to a broad t r i p l e t at x 8.01, J=2.5Hz, and the C, methine s i g n a l at 7.40 collapsed to a doublet. The 6  remainder of the spectrum was unchanged.  Thermolysis of Enone A l c o h o l 106. Enone a l c o h o l 106 (10 mg, 0.049 mmol) was placed i n a sealed ampoule and heated to 200° f o r 5 hours.  The dark product was taken  up i n chloroform and eluted through a short column of alumina to give 5 mg of product, i d e n t i f i e d as ene-dione 107 by glpc r e t e n t i o n time and i r spectrum.  P h o t o l y s i s of Enone A l c o h o l 106 i n t e r t - B u t a n o l . A s o l u t i o n of 15 mg (0.073 mmol) of 106 i n 8 ml of 10% benzene/ tert-butanol. (v/v) was i r r a d i a t e d as u s u a l , the r e a c t i o n being monitored by glpc (column A, 175°, 160 ml/min).  A f t e r 5 hours,  complete r e a c t i o n had occurred, and the product i s o l a t e d by chromatography  (alumina, chloroform) - 10 mg (67%) - was i d e n t i f i e d  as ene-dione 107 on the b a s i s of glpc r e t e n t i o n time, i r and nmr spectra.  - 147 -  P h o t o l y s i s of Enone A l c o h o l 106 i n Benzene. A s o l u t i o n of 64 mg (0.31 mmol) of 106 i n 30 ml of benzene was  i r r a d i a t e d as usual.  A f t e r 26 hours, glpc showed the r e a c t i o n  was about 85% complete, with two products being formed,  subsequently  i d e n t i f i e d as ene-dione 107 and ene-dione 108. The r e l a t i v e r a t i o was  106:107:108 = 1:3.2:3.6.  A f t e r evaporation and column chromatography  ( S i l i c a G e l , 25% e t h y l acetate/benzene), 108 were i s o l a t e d .  20 mg of 107 and 23 mg of  Each was i d e n t i f i e d by comparison of glpc  r e t e n t i o n times, i r and nmr spectra to those of authentic samples. I t was shown that 108 does not rearrange under the conditions of g l p c , and therefore 107 i s a true photoproduct from 106.  Thermolysis  of Enone A l c o h o l 109.  Compound 109 (14 nig, 0.07  mmol) was placed i n a sealed ampoule  and heated f o r 3 hours at 200°.  Glpc showed two products,  corresponding  i n r e t e n t i o n times to ene-diones 107 and 110, i n a r a t i o of 1:3.2. Owing to the small quantity of m a t e r i a l a v a i l a b l e , only 110 was i s o l a t e d s u c c e s s f u l l y which showed i r and nmr spectra i d e n t i c a l to those of an authentic sample obtained from the p h o t o l y s i s of adduct jj>5_ i n t e r t - b u t a n o l .  P h o t o l y s i s of 109 i n t e r t - B u t a n o l . A s o l u t i o n of 25 mg (0.12 mmol) of 109 i n 10 ml of 10% benzene/ t e r t - b u t a n o l was  i r r a d i a t e d f o r 19 hours, a t which time glpc showed  - 1A8 complete conversion to photoproduct 110. Column chromatography afforded 16 mg (64%) of 110, i d e n t i f i e d by i t s glpc r e t e n t i o n time, i r and nmr spectra.  P h o t o l y s i s of Enone A l c o h o l 109 i n Benzene. A s o l u t i o n of 6 mg (0.03 mmol) of 109 i n 3 ml of benzene was i r r a d i a t e d as usual.  Glpc showed only a gradual disappearance  of 109 w i t h no v o l a t i l e products being formed. r e a c t i o n was stopped;  A f t e r 45 hours, the  a l l 109 was gone, and no product appeared.  Thermolysis of Ene-Dione 108. Compound 108 (5 mg, 0.024 mmol) was placed i n a sealed ampoule and heated at 182° f o r 5 hours.  The golden product was checked  by g l p c , which showed the presence of a s i n g l e product, i d e n t i f i e d as ene-dione 107 by i t s r e t e n t i o n time and i r spectrum.  6, 7-Dimethyl-2-phenyl-4a3,5,8,8aB-tetrahydro-l, 4-naphthoquinone  (96) i *  9  A s l u r r y of 3.5 g (0.019 moles) of phenyl-p_-benzoquinone (Eastman, r e c r y s t a l l i z e d from petroleum ether p r i o r to use), 7.3 g (0.089 moles) of 2,3-dimethyl-l,3-butadiene, and a few c r y s t a l s of hydroquinone was heated i n a sealed Pyrex tube f o r 1 hour at 100°. O n c o o l i n g , the deep amber mixture s o l i d i f i e d to a yellow mass, which was washed w i t h acetone.  R e c r y s t a l l i z a t i o n twice from petroleum  ether (68°) r e s u l t e d i n 3.68 g (73%) of 96 as a l i g h t yellow s o l i d ,  - 149  -  mp 108 - 109.5° ( l i t ! * 1 1 3 - 114°).  D i s t i n g u i s h i n g s p e c t r a l features  9  were: 3.33 8.0  i r (CCl^) 5.94 ( s , 1, C  3  uv max  nmr  v i n y l ) , 6.5 - 7.0  (m, 4, C„ and C D  (C=0)y;  ( C C l ^ x 2.60  (m, 2,  methylenes), 8.33  D  O  ( s , 5, phenyl),  and C  ga  methines), 7.5  -  (s, 6, Q, and C-. methyls);  fa  /  (methanol) 225 (log e 4.57), 301 nm (log e 3.98).  P h o t o l y s i s of 96^ i n Benzene. A s o l u t i o n of 211 mg  (0.8 mmol) of 96_ i n 50 ml of benzene  was i r r a d i a t e d w i t h l i g h t of wavelength  340 run.  The r e a c t i o n  was monitored by i r spectroscopy which showed a f a i r l y r a p i d change i n the f i n g e r p r i n t region.  This was accompanied by a more gradual  buildup of a 5.70y peak u n t i l a f t e r 18.5 hours, i t was the only carbonyl s i g n a l present.  virtually  Evaporation of solvent followed  by column chromatography ( S i l i c a Gel, 15% e t h y l r e s u l t e d i n 95 mg of pale yellow o i l .  acetate/benzene)  A second chromatography  ( S i l i c a G e l , chloroform) y i e l d e d 83 mg of o i l which c r y s t a l l i z e d on standing to c o l o r l e s s c r y s t a l s . petroleum ether (38°)  r  R e c r y s t a l l i z a t i o n from ether/  gave 70 mg (33%) of 8,9-dimethyl-3-phenyltricyclo-  3 7l  [4.4.0.0 '  dec-8-ene-2,5-dione (117) as c o l o r l e s s c r y s t a l s , mp  109 - 110°C, i d e n t i f i e d on the b a s i s of the f o l l o w i n g s p e c t r a l data: i r (CC1 ) 5.70 4  (C=0)y;  1, J=18Hz, 1.5 Hz, C 7.50  (br s, 2 ) , 7.62  3, Cg or C  g  4  nmr  ( C D C l ) l 2.64 3  exo-methylene), (d, 1, J=18Hz,  methyl), 8.69  ( s , 3, C  g  7.23  ( s , 5, phenyl), 7.06 (br s, 1), 7.2 - 7.4  endo-methylene), 8.32 or C  g  (dd,  methyl);  uv max  (m, 2 ) ,  (s, (methanol)  a long f e a t u r e l e s s absorption (e at 252 nm 800, e at 290 nm 140); mass spectrum (70 eV) m/e parent 266. Anal. 81.09;  Calcd. f o r C. H. 0 : o  H, 6.73.  lo  o  lo  o  C, 81.17;  H, 6.81. Found:  C,  Z  Base Catalyzed Deuterium Exchange of Ene-Dione 117. To a deuterochloroform s o l u t i o n of 117 i n an nmr tube was added 8 drops of a 1.2 N s o l u t i o n of potassium hydroxide i n D2O. A f t e r p e r i o d i c shaking f o r one day, the nmr spectrum was measured, and the f o l l o w i n g changes noted:  the double doublet at T7.06 due  to the C^ exo-proton had disappeared completely; the doublet a t T7.62 due to C^ endo-proton collapsed to a broad s i n g l e t ;  the  remainder of the spectrum remained unchanged.  Short Period P h o t o l y s i s of 9_6 i n Benzene. A s o l u t i o n of 500 mg (1.9 mmol) of 96_ i n 125 ml of benzene was i r r a d i a t e d w i t h l i g h t of wavelength > 340 nm, and the r e a c t i o n was i n t e r r u p t e d a f t e r 3.5 hours at which time the i r spectrum of an a l i q u o t showed the presence of 2 carbonyls at 5.70 and 5.93y. Chromatography  of the i n t e n s e l y yellow s o l u t i o n ( S i l i c a Gel, 25%  e t h y l acetate/benzene) y i e l d e d 42 mg of ene-dione 117 and 102 mg of a yellow o i l , the i r of which showed 1 carbonyl at 5.93M> plus the presence of OH.  The nmr spectrum of t h i s l a t t e r m a t e r i a l  i n d i c a t e d a mixture of 2 isomeric enone a l c o h o l s 120 and 121 i n a  - 151 r a t i o of about 6:1  (from i n t e g r a t i o n ) .  Chromatography o f t h i s  mixture ( S i l i c a G e l , 8% e t h y l acetate/benzene) was accompanied by a good d e a l of decomposition, but allowed f o r p a r t i a l separation of the isomers.  A f t e r passing each through a short column of alumina  (chloroform e l u e n t ) , 25 mg of 120 and 14 mg of 121 were obtained, each of which s o l i d i f i e d i n a small amount of petroleum ether. I d e n t i f i c a t i o n was based on the f o l l o w i n g s p e c t r a l data:  r  a  5  for 120, 8,9-dimethyl-5-hydroxy-3-phenyltricyclo14.4.0.0 'J deca3,7-diene-2-one: nmr ( C C ± ) T 2.6 C-, v i n y l ) , 6.87 /  mp 68 - 70°;  i r (CC1 ) 2.80  (OH), 5.92  4  (m, 5, phenyl), 3.20 ( s , 1, C v i n y l ) , 4.37 (m, 1, (d, 1, J=3Hz, C, methine), 7.50 ( s , 1, OH), 7.4 o 4  4  7.8  (m. 1. C. methine), 8.21 i  8.5  (m, 2, C^Q methylenes), 8.83  (d. 3. J=1.5Hz, C methyl), 8.3 ' o Q  ( s , 3, C^ methyl);  220 (e 6200), 270 (e 3800), sh 340 nm (e 61); m/e  (C=0)y;  uv max  (methanol)  mass spectrum (70 eV)  parent 266.  r  591  for 121, 8,9-dimethyl-5-hydroxy-4-phenyltricyclo 4.4.0.0 ' Jdeca3,7-diene-2-one:  mp 103 - 106°;  i r (KBr) 2.9 (OH), 6.03  nmr ( C C l ^ T 2.7 (m, 5, phenyl), 4.03 (d, 1, J=1.5Hz, C 4.32*(m, 1, C_ v i n y l ) , 6.86 (br d, 1, C, methine), 7.60 / o 3  7.4 - 7.8 8.5  (m, 1, C  (m, 2, C  1 Q  1  methine), 8.20  methylenes), 8.75  (br s, 3, C  g  parent  266.  vinyl), ( s , 1, OH),  methyl), 8.3 -  ( s , 3, C^ methyl);  uv max  281 (c 5400), a t a i l i n g absorption (e at 345 nm = 105); (70 eV) m/e  (C=0)y;  (methanol)  mass spectrum  - 152 Samples of both 120 and 121 were q u i t e impure, and owing to l a c k of m a t e r i a l , the usual p u r i f i c a t i o n procedures (sublimation, r e c r y s t a l l i z a t i o were not s u c c e s s f u l .  Thus high r e s o l u t i o n mass spectra were obtained:  Calcd. f o r C H . 0 = 266.1306 lo l o 2 1Q  for 120:  o  o  observed 266.1285 (A = 0.0021)  for 121: observed 266.1349 (A = 0.0043)  P h o t o l y s i s of Adduct 96^ i n t e r t - B u t a n o l . A s o l u t i o n of 150 mg (0.56 mmol) of j)6_ i n 50 ml of 10% benzenet e r t - b u t a n o l was i r r a d i a t e d f o r 24 hours. followed by chromatography  Evaporation of solvent  through a short column of alumina (chloroform)  gave 113 mg of yellow o i l .  The i r showed one main carbonyl band  at 5.70u and a small, shoulder a t 5.9y. Chromatography on S i l i c a G e l (10%  e t h y l acetate/benzene), which was accompanied by a great deal  of decomposition, y i e l d e d 43 mg (29%) of ene-dione 117, i d e n t i c a l w i t h that obtained from the benzene p h o t o l y s i s , and a t r a c e of m a t e r i a l , the i r and nmr spectra of which showed the sample to be a mixture of isomers 120 and 121 i n a r a t i o of approximately 6:1.  P h o t o l y s i s of j)6_ i n tert-Butanol-0-d. A s o l u t i o n of 90 mg (0.34 mmol) of 96_ i n 10 ml of t e r t - b u t a n o l 0-d was i r r a d i a t e d f o r 6 hours. by column chromatography  The ene-dione subsequently i s o l a t e d  ( S i l i c a Gel - 8% e t h y l acetate/benzene)  showed an nmr spectrum i d e n t i c a l w i t h that obtained from the basecatalyzed deuterium exchange of ene-dione 117, i n d i c a t i n g deuterium  - 153 i n c o r p o r a t i o n had occurred at the  exo-position.  From the mass  spectrum, i t was c a l c u l a t e d that 90% deuterium i n c o r p o r a t i o n had occurred (see Appendix f o r c a l c u l a t i o n ) .  Manganese Dioxide. This m a t e r i a l was prepared i n the same way as that described by Attenburrow et a l f o r " a c t i v e " manganese d i o x i d e . 6 0  A s o l u t i o n of  38.4 g (0.24 mole) of potassium permanganate i n 250 ml water was heated on a hot plate/magnetic s t i r r e r .  Meanwhile s o l u t i o n s of 44 g  (0.2 mole) of manganese sulphate tetrahydrate i n 100 ml of water and 18.8 g (0.48 mole) of sodium hydroxide i n 70 ml of water were prepared. Then, w i t h s t i r r i n g , these two s o l u t i o n s were added simultaneously to the hot permanganate s o l u t i o n . almost immediately.  A f i n e brown p r e c i p i t a t e formed  S t i r r i n g was continued f o r an a d d i t i o n a l hour,  a f t e r which the mixture was f i l t e r e d w i t h s u c t i o n .  The s o l i d was  washed w i t h s e v e r a l portions of water u n t i l the f i l t r a t e was  colorless;  then i t was washed w i t h acetone, d r i e d i n an oven at 110°, and ground to a powder.  Y i e l d was 45 gm.  2,3-Dimethyl-l,4-benzoquinone (129). This p r e p a r a t i o n w a s c a r r i e d out i n the f o l l o w i n g apparatus: 59  a 2 l i t r e , 3 neck round bottom r e c e i v i n g f l a s k , equipped w i t h an e f f i c i e n t condenser, was submerged i n an i c e water bath.  To one neck  was f i t t e d , by means of a bent adaptor, a second condenser which  - 154  -  was connected to the side arm of a 500 ml d i s t i l l a t i o n f l a s k set up f o r steam d i s t i l l a t i o n .  The t h i r d neck of the r e c e i v e r was stoppered.  To the 500 ml f l a s k were added 8 g (0.07 mole) of 2,3-dimethylaniline, 16 ml of concentrated s u l p h u r i c a c i d , and 100 ml of water.  After  thorough mixing of reagents, and w i t h the c o o l i n g water running, 24 g (0.28 mole) of manganese dioxide were introduced to the f l a s k , the f l a s k b r i e f l y s w i r l e d , and steam d i s t i l l a t i o n s t a r t e d immediately. When the water d i s t i l l i n g over became c o l o r l e s s , the apparatus was disconnected, and both condensers were r i n s e d w i t h ether.  The  contents of the r e c e i v i n g f l a s k were d i l u t e d w i t h 100 ml of water, and the mixture was extracted w i t h 3 x 150 ml portions of ether. The combined ether e x t r a c t s were washed w i t h 100 ml of water, d r i e d over sodium sulphate, f i l t e r e d , and evaporated i n vacuo at room temperature to give 3.6 g (38%) of 129 as a yellow c r y s t a l l i n e s o l i d . This was used without f u r t h e r p u r i f i c a t i o n .  4a3,5,8,8a3-Tetrahydro-2,3,6,7-Tetramethyl-i,4-naphthoquinone  (97).  Following the procedure reported by F i e s e r and Chang a mixture 58  of 1.65 g (0.012 mole) of 2,3-dimethyl-l,4-benzoquinone (129) and 2.92 g (0.036 mole) of 2,3-dimethyl-l,3-butadiene i n 5 ml of ethanol was r e f l u x e d f o r 10 hours. to a mass.  On c o o l i n g , the reaction, mixture s o l i d i f i e d  R e c r y s t a l l i z a t i o n from ethanol y i e l d e d 2.11 g (81%) of 97_  as s m a l l , c o l o r l e s s c r y s t a l s , mp 104.5 - 105° ( l i t 1 0 5 - 106.5°). 5 8  D i s t i n g u i s h i n g s p e c t r a l features were as f o l l o w s :  uv max  (methanol)  -  155  253 (e 9420), 330 nm (e 115); and C  -  I r (CCl^) 5.95  6.95  (m, 2,  8.07  ( s , 6, C„ and C_ methyls), 8.35 Z  ga  methines), 7.85  (C=0)y;  (m, 4, C,. and C  D  parent  (CCl )x 4  methylenes),  g  ( s , 6, C, and C., methyls);  J  mass spectrum (70 eV) m/e  nmr  /  218.  P h o t o l y s i s of Adduct 97_ i n Benzene. A s o l u t i o n of 600 mg  (2.8 mmol) of 97_ i n 200 ml of benzene  was placed i n a Pyrex v e s s e l and i r r a d i a t e d w i t h l i g h t of wavelength A. >^ 340 nm. 160°,  The r e a c t i o n was monitored by a n a l y t i c a l glpc (column A,  150 ml/min.), which showed complete r e a c t i o n of 9_7_ had occurred  a f t e r 6.5 hours w i t h the formation of one photoproduct.  After  evaporation of s o l v e n t , the residue was subjected to column chromatography on 40 g of S i l i c a Gel using 20% e t h y l acetate/benzene solvent.  This r e s u l t e d i n the i s o l a t i o n of 137 mg  as the e l u t i n g  (23%) of c r y s t a l l i n e  m a t e r i a l , mp 55 - 56°, i d e n t i f i e d as 5-hydroxy-3,4,8,9-tetramethyltricyclo [4.4.0.0 ' Jdeca-3,7-diene-2-one (130) on the b a s i s of the f o l l o w i n g s p e c t r a l data: (KBr) 2.94 7.13  uv max  (OH), 6.05  (methanol) 252 (C=0)y;  nmr  (e 8600), 325 nm  ( C D C l ^ T 4.42  (d, 1, J=3Hz, C, methine), 7.70  (e 80);  ir  (m, 1, v i n y l H),  ( s , 1, disappears on adding  o  OH),  7.84  J=1.5Hz, C  (m, 1, g  the C^Q methylenes), 8.65 (s, 3, C  Q  methyl)5  o  Z  methine), 8.16  methyl), 8.30  D 0,  ( s , 3, C  ( s , 3, C^ methyl), 8.25 3  methyl), 8.59  ( s , 1, the other  mass spectrum (70 eV) m/e  (d, 3,  (d, 1, J=3Hz, o n e o f  methylene), parent 2 1 8 .  8.93  156  -  Anal. 77.10;  H,  Calcd. f o r  c  H 1 4  0 1 8  i  c  2  »  7  7  -  0  3  5  H  » - > 8  Found:  31  C,  8.44.  P h o t o l y s i s of Adduct 97_ i n t e r t - B u t y l A l c o h o l . Compound 9_7 (110 mg,  0.5 mmol) i n 20 ml of t e r t - b u t a n o l was  placed i n a quartz tube and i r r a d i a t e d w i t h l i g h t of wavelength _> 340 nm.  A n a l y t i c a l glpc (column A, 170°,  150 ml/min) showed  complete r e a c t i o n of 91_ a f t e r 4.5 hours and the formation of two photoproducts  i n a r a t i o of about 2:1;  the products were i s o l a t e d  by p r e p a r a t i v e glpc (same conditions as above). 17 mg  The minor product,  (15%), was i d e n t i f i e d as enone-alcohol 130, i d e n t i c a l i n a l l  p r o p e r t i e s (glpc r e t e n t i o n time, mp,  s p e c t r a l data) to that i s o l a t e d  from the p h o t o l y s i s of 97_ i n benzene.  Of the major product, 36 mg  (33%) were obtained which, on r e c r y s t a l l i z a t i o n from petroleum ether (68°), formed c o l o r l e s s c r y s t a l s , mp 88.5 - 89°.  On the b a s i s of the  f o l l o w i n g s p e c t r a l data, t h i s product was assigned the s t r u c t u r e 3,4,8,9-tetramethyltricyclo ^4.4.0.0 ' ] dec-8-ene-2,5-dione (131): 3  uv max 7.24  (methanol) 290 nm (e 57);  7  i r (KBr).5.74 (C=0)y;  (dd, 1, J. =1.5Hz, 3 ,=2Kz, C, methine), 7.5 - 7.8 6,4 6,1 o C  m u l t i p l e t , 4 ) , 7.73  (dd, 1, J .  =1.5Hz, J=7Hz, C. methine),  (s, 3, C 3  m/e  g  g  methyl), 9.09 parent Anal.  H,  or C  8.36.  methyl), 8.40  (CDC1 )T 3  (complex 8.25  4  4,0  C  nmr  ( s , 3, C  g  or C  (d, 3, J=7Hz, C^ methyl);  Q  methyl), 8.85  ( s , 3,  mass spectrum (70 eV)  218. Calcd. f o r C..H 0 : 14 l o 2 lo  o  C, 77.03;  H, 8.31.  Found:  C, 76.80;  -  157 -  B a s e - C a t a l y z e d Deuterium Exchange o f Ene-Dione J_31. A s o l u t i o n of 15 mg (0.07 mmol) o f ene-dione 131 i n 0.5 ml o f CDCl^ i n an nmr tube was t r e a t e d w i t h 10 drops o f a 1.2 N s o l u t i o n of potassium h y d r o x i d e d i s s o l v e d  i n deuterium o x i d e .  The tube was  shaken r e p e a t e d l y and the exchange was f o l l o w e d by nmr s p e c t r o s c o p y , which showed a slow exchange  of the C^ methine p r o t o n .  A f t e r 14  days, t h e exchange was complete, and nmr showed 1 p r o t o n had exchanged.  The d i f f e r e n c e s between the nmr o f d e u t e r i o - e n e - d i o n e  131 and p r o t i o - e n e - d i o n e 131 were as f o l l o w s : d o u b l e t s a t T7.24 (C^ methine) (J=2Hz);  the s i g n a l a t Tl.13  the d o u b l e t o f  i n the l a t t e r c o l l a p s e d to a doublet (due t o C^ methine) d i s a p p e a r e d ; t h e  d o u b l e t a t 9.09 (C^ methyl) c o l l a p s e d t o a broad s i n g l e t . f e a t u r e s remained  Other  unchanged.  Attempted T h e r m o l y s i s o f Enone A l c o h o l 130 under P h o t o l y s i s Enone a l c o h o l was  130 (15 mg, 0.07 mmol) i n 3 ml o f t e r t - b u t a n o l  heated to 65° ( r e p r e s e n t i n g extreme  ampoule.  Conditions.  conditions) i n a sealed  The m i x t u r e was t e s t e d a f t e r 23 hours and 45 hours by  a n a l y t i c a l glpc  (column A, 160°, 150 ml/min).  had o c c u r r e d , and enone a l c o h o l  No d e t e c t a b l e  reaction  130 was r e c o v e r e d unchanged.  Attempted P h o t o l y s i s o f Enone A l c o h o l 130 i n Benzene. A s o l u t i o n o f 50 mg (0.23 mmol) of 130 i n 10 ml o f benzene i n the q u a r t z tube was i r r a d i a t e d as u s u a l  (X >_ 340 nm).  The r e a c t i o n  - 158 was monitored by glpc (same conditions as above) which showed no detectable r e a c t i o n a f t e r 28 hours.  S t a r t i n g m a t e r i a l was  recovered  unchanged.  P h o t o l y s i s of Enone A l c o h o l 130 i n t e r t - B u t a n o l . A s o l u t i o n of 52 mg was  (0.24 mmol) of 130 i n 10 ml of t e r t - b u t a n o l  i r r a d i a t e d i n the usual manner.  The r e a c t i o n was monitored  by glpc (same conditions) which showed complete conversion to ene-dione 131 a f t e r 6 hours ( i d e n t i f i c a t i o n based on r e t e n t i o n time from glpc c o - i n j e c t i o n of authentic sample).  No intermediate could be detected  during the course of the transformation.  2,3-Dicyano-l,4-benzoquinone (135). Using a s l i g h t l y modified procedure of B r o o k e x c e s s nitrogen 62  dioxide was temperature. the N^O^  condensed i n a small f l a s k cooled to l i q u i d nitrogen The f l a s k was  then allowed to warm up s l o w l y , and as  melted, i t was added dropwise, w i t h s t i r r i n g , to a magnetically  s t i r r e d suspension of 10 g (0.063 moles) of 2,3-dicyanohydroquinone ( A l d r i c h ) i n 50 ml of carbon t e t r a c h l o r i d e contained i n a 125 ml Erlenmeyer f l a s k .  The greenish suspension r a p i d l y became yellow;  s t i r r i n g was continued an a d d i t i o n a l % hour.  A f t e r the excess  ^ 0 ^ was removed as N0^ w i t h a stream of n i t r o g e n , the product c o l l e c t e d by s u c t i o n f i l t r a t i o n .  was  Y i e l d was 9.6 g (97%) of quinone  135 as a yellow s o l i d , mp 176 - 178°  ( l i t 1 7 8 - 180°). 6 2  This m a t e r i a l  - 159 -  was found to be s u f f i c i e n t l y pure f o r subsequent D i e l s - A l d e r r e a c t i o n s and was used without f u r t h e r p u r i f i c a t i o n .  4a8,8aB-Dicyano-6,7-dimethyl-4a,5,8,8a-tetrahydro-l,4-naphthoquinone  (98).  Following the reported procedure of A n s e l l , et a l t o a s o l u t i o n 8 3  of 2.5 g (0.016 mole) of 2,3-dicyano-l,4-benzoquinone (135) i n 100 ml of benzene-ethanol (9:1 v/v) was added 2.5 g (0.030 mole) of 2,3dimethyl-1,3-butadiene.  The r e a c t i o n mixture was allowed to stand a t  room temperature f o r 18 hours, a f t e r which i t was evaporated to dryness.  The r e s u l t i n g s o l i d was r e c r y s t a l l i z e d twice from acetone/  petroleum ether (68°) to g i v e pale yellow c r y s t a l s of 98_, mp 158 159° ( l i t 1 5 7 - 158°). 6 3  The y i e l d was 2.85 g (75%), and d i s t i n g u i s h i n g  s p e c t r a l features were as f o l l o w s : and 5.86 (C=0)y; (br s, 4, C  c  D  i r (KBr) 4.43 (weak, C=N), 5.79  nmr (CDCl )x 3.06 ( s , 2, C  and C  3  0  2  and C  3  v i n y l s ) , 7.28  methylenes), 8.30 ( s , 6, C, and C, methyls);  O  O  /  uv max (methanol) 225 nm (£ 8900), a long f e a t u r e l e s s t a i l i n g absorption (e at 340 nm = 93);  mass spectrum (70 eV) m/e parent 240.  P h o t o l y s i s of Compound 98 i n t e r t - B u t a n o l . A s o l u t i o n of 485 mg of j)8_ (2 mmol) i n 250 ml of 10% benzenet e r t - b u t a n o l was i r r a d i a t e d and the r e a c t i o n followed by glpc (column C, 180°, 160 ml/min) which showed no s t a r t i n g m a t e r i a l remaining a f t e r 3 hours.  Evaporation of solvents l e f t a pale brown residue which,  on t r i t u r a t i o n w i t h benzene followed by f i l t r a t i o n , l e f t 265 mg of  - 160 colorless s o l i d .  R e c r y s t a l l i z a t i o n of the s o l i d from acetone-  petroleum ether (68°) gave 240 mg (50%) of  T  1,6-dicyano-8,9-dimethyl-5-  5 9l  h y d r o x y t r i c y c l o 4.4.0.0 ' Jdeca-3,7-diene-2-one c r y s t a l s , mp 188 - 190°.  The s t r u c t u r e was deduced from the f o l l o w i n g  spectral characteristics: 5.87  (C=0)y;  nmr  (d, 1, J=10Hz, C  3  7.7 - 8.2  i r (KBr) 2.90  (acetone-dg)! 2.99 v i n y l ) , 4.07  on adding D2O, OH), 7.67  (136) as c o l o r l e s s  (OH), 4.41  (d, 1, J=10Hz, C  (m, 1, C  ?  v i n y l ) , 3.69  4  v i n y l ) , 7.19  ( s , 1, disappears  (d, 1, J=13Hz, one of C^Q methylenes),  (m, other C^Q methylene and acetone resonances), 8.03  (d, 3, J=1.5Hz, Cg methyl), 8.73  (s, 3, C  g  methyl);  239 (e 3800), t a i l i n g absorption (e at 315 = 141); (70 eV) m/e Anal. Found:  (weak, C S N ) ,  uv max  (methanol)  mass spectrum  parent 240. Calcd. f o r C  C, 69.87;  H 1 4  N 1 2  H, 4.96;  2°2  :  C, 69.99;  H, 5.03;  N, 11.66.  N , 11.63.  Meanwhile, the benzene e x t r a c t was evaporated to g i v e 287 mg of pale yellow o i l .  Following column chromatography ( S i l i c a Gel, 33% e t h y l  acetate-benzene), 175 mg of 137 were obtained as a c o l o r l e s s o i l , the mass spectrum of which showed a parent i o n at 314, i n d i c a t i n g the a d d i t i o n of one molecule of t e r t - b u t a n o l had occurred. for s p e c t r a l data and conclusions.  See d i s c u s s i o n  ,  P h o t o l y s i s of Enone A l c o h o l 136 i n t e r t - B u t a n o l . , A s o l u t i o n of 28 mg was  (0.12 mmol) of 136 i n 10 ml of t e r t - b u t a n o l  i r r a d i a t e d f o r 18 hours.  A f t e r evaporation of the s o l v e n t ,  i r and nmr spectra showed no 136 remained;  these spectra  were  - 161 i d e n t i c a l to those of 137 obtained from the p h o t o l y s i s of 9J8 i n tert-butanol.  P h o t o l y s i s of  i n Acetonitrile.  A s o l u t i o n of 80 mg (0.33 mmol) of 9j8 i n 25 ml of a c e t o n i t r i l e was photolyzed f o r 2 hours.  A f t e r evaporation i n vacuo, followed  by chromatography (alumina, ether) 47 mg (59%) of enone a l c o h o l 136 were obtained, i d e n t i f i e d by melting p o i n t , i r and nmr spectra. No other product was detected or i s o l a t e d .  P h o t o l y s i s of 9_8 i n Methanol. A s o l u t i o n of 97 mg (0.4 mmol) of 9_8 i n 50 ml of anhydrous methanol was i r r a d i a t e d f o r 1 hour.  Evaporation of solvent followed  by column chromatography gave 35 mg of unreacted 9_8 and 20 mg (32%, based on recovered s t a r t i n g m a t e r i a l ) of enone a l c o h o l 136. Again, no other product was detected.  Attempted Thermolysis of Enone A l c o h o l 136. Compound 136 (25 mg, 0.1 mmol) was heated at 185° i n a sealed tube f o r 14 hours.  The dark brown product was extracted w i t h  chloroform which gave 21 mg of a brown gum.  I r showed the presence  of carbonyl s t r e t c h e s at 5.68, 5.80 sh and 5.85. However, t i c ( S i l i c a G e l , 25% e t h y l acetate/benzene)  showed the presence of s e v e r a l  products, so the m a t e r i a l was not i n v e s t i g a t e d f u r t h e r .  -  162  -  2,3-Dichloro-5,6-dicyano-l,4-benzoquinone A m i x t u r e of 5 g (0.031 moles) of (Aldrich)  (141)  6 6  2,3-dicyanohydroquinone  i n 70 ml of 50% aqueous h y d r o c h l o r i c  a c i d was  placed i n  a 250 ml Erlenmeyer  f l a s k equipped w i t h a magnetic  stirring  and warmed to 35°.  Then, over a 45 minute p e r i o d ,  9.4  nitric  a c i d was  added w i t h s t i r r i n g ;  became y e l l o w .  After  Dissolving  and f i n a l l y 141, mp 4.42  complete,  then  was  filtered  r e s u l t i n g i n a d i r t y yellow  t h i s i n hot benzene, t r e a t i n g w i t h N o r i t , f i l t e r i n g  evaporating the solvent j  left  202 - 204° ( l i t ! 2 1 2 - 2 1 3 ° ) ; 6  (C=N), 5.94  stirring  The m i x t u r e was  and washed w i t h carbon t e t r a c h l o r i d e , solid.  g of c o n c e n t r a t e d  the m i x t u r e foamed a b i t and  the a d d i t i o n was  c o n t i n u e d f o r an a d d i t i o n a l hour.  bar  (C=0),  12.5  (C-Cl)y.  6.8  g (96%) of y e l l o w s o l i d  i r (KBr) no C-H  stretch,  The p r o d u c t was  used i n the  next s t e p w i t h o u t f u r t h e r p u r i f i c a t i o n .  2,3-Dichloro-4ap,8a8-dicyano-6,7-dimethyl-4a,5,8,8a-tetrahydro-1,4naphthoquinone  (99).  To a s o l u t i o n of 4.16 was  added 1.5  g (0.018 mole) of 141  i n 100 ml of  g (0.019 mole) o f 2 , 3 - d i m e t h y l - l , 3 - b u t a d i e n e .  m i x t u r e r a p i d l y became green i n c o l o r and s l i g h t l y warm. allowing was  the s o l u t i o n to stand a t room temperature  evaporated to g i v e a greenish-brown  from methanol 99, mp  resulted  i n 4.5  residue.  The  reaction  After  f o r 1 hour,  solvent  Recrystallization  g (81%) of green c o l o r e d  178 - 179°, i d e n t i f i e d by the f o l l o w i n g  methanol  c r y s t a l s of  properties;  - 163 i r (KBr) 5.82  (C=0), 12.62  and Cg methylenes), 8.28 270 nm  (C-Cl)y;  nmr  ( C D C 1 ) T 7.23  ( s , 4,  3  (s, 6, v i n y l methyls);  uv max  C  5  (methanol)  (e 6000) and a long f e a t u r e l e s s absorption from 300 to 360  (e at 340 nm = 400); Anal. N, 9.06.  mass spectrum (70 eV) m/e  Calcd. f o r Found:  C 1  4  H  C 1 1 0  C, 54.58;  N 2  2°2  :  C  '  H, 3.26;  5 4  '  parent 308, 310,  3 9 ;  H  >  C l , 22.70;  3  -  2  N,  6  5  cl  »  312.  22.94;  9.18.  P h o t o l y s i s of 97 i n t e r t - B u t a n o l . A s o l u t i o n of 600 mg  (2 mmol) of S>9_ i n 300 ml t e r t - b u t a n o l was  i r r a d i a t e d , and the course of the r e a c t i o n was monitored by glpc (column C, 180°,  180 ml/min) which showed complete r e a c t i o n of  s t a r t i n g m a t e r i a l a f t e r 24 hours.  Evaporation of the now  yellow  s o l u t i o n r e s u l t e d i n a reddish residue which was d i s s o l v e d i n 100 ml of ether, washed w i t h 4 x 15 ml water, 4 x 15 ml sodium bicarbonate, and 4 x 15 ml water.  A f t e r drying (Na^SO^), the ether was  to give 400 mg of pale yellow s o l i d . methanol-water twice gave 250 mg  evaporated  R e c r y s t a l l i z a t i o n from  (42%) of c o l o r l e s s needles,  mp  226 - 228°, i d e n t i f i e d as 3,4-dichloro-l,6-dicyano-8,9-diraethyl,o.o >9 5-hydroxytricyclo 4.4.0.0 ' deca-3,7-diene-2-one (142) on the b a s i s 5  of the f o l l o w i n g s p e c t r a l data: 12.45  (C-Cl)y;  nmr  i r (KBr) 2.92  (acetone-d,)T 4.07 o  (m, 1, C-, v i n y l ) , /  (br s, 1, disappears on adding D2O, OH), 7.47 J=14Hz, C (s, 3, C  g  1Q  methylenes), 8.02  and 7.81  (d, 3, J=1.5Hz, C  methyl), the T values f o r the  (OH), 5.90  g  (C=0), 7.07  (each d, 2,  methyl),  8.67  methylenes were c a l c u l a t e d  5  - 164 uv max (MeOH) 265 nm (e 9100);  mass spectrum (70 eV) m/e parent  308, 310, 312. A sample was sublimed at 190° and 0.01 t o r r to give an a n a l y t i c a l sample. Anal. N, 9.06.  Calcd. f o r Found:  c 1  4  H  c l 1 0  C, 54.13;  N 2  2 2 O  °'  :  5 4  *  3 9 ;  H  » - '>  H, 3.15; C l , 22.92;  2,3-Dicarbomethoxy-l,4-benzoquinone  3  26  c l  » 22.94;  N, 8.76.  (145).  Following the procedure of A n s e l l , et a l 5 g (0.031 mole) of 6 7  2,3-dicyanohydroquinone ( A l d r i c h ) was added to a s o l u t i o n of 40 g of potassium hydroxide i n 40 ml of d i s t i l l e d water and the mixture r e f l u x e d f o r 75 minutes under a nitrogen atmosphere.  The now dark  mixture was then a c i d i f i e d w i t h excess, i c e cold 7N s u l f u r i c a c i d and extracted w i t h s i x 50 ml portions of e t h y l acetate.  A f t e r drying  (Na2S0^), f i l t r a t i o n , and evaporation of s o l v e n t , 5.3 g of l i g h t brown s o l i d was obtained. R e c r y s t a l l i z a t i o n from water gave 2.4 g (39%) of 3,6-dihydroxyphthalic a c i d (143), mp 214.5 - 216° ( l i t 213° dec) as a l i g h t brown s o l i d .  6 7  This was e s t e r i f i e d as f o l l o w s :  a mixture of 2.4 g of d i a c i d i n 50 ml of methanol plus 3 ml cone s u l f u r i c a c i d was r e f l u x e d .overnight.  The methanol was then removed  i n vacuo l e a v i n g a damp white s o l i d residue which was washed w i t h water and c o l l e c t e d by s u c t i o n f i l t r a t i o n .  The f i l t e r cake was  repeatedly washed w i t h small portions of cold d i s t i l l e d water u n t i l the washings were n e u t r a l .  R e c r y s t a l l i z a t i o n from water gave 1.19 g  (43%) of 3,6-dihydroxydimethylphthalate (144) as c o l o r l e s s c r y s t a l s ,  - 165 mp 131 - 133° ( l i t ? 1 4 1 - 142°). 7  The above d i e s t e r was suspended i n 40 ml of carbon t e t r a c h l o r i d e . Then, w i t h s t i r r i n g , excess d i n i t r o g e n t e t r o x i d e (nitrogen dioxide condensed i n t o a f l a s k at -196°) was added dropwise, whereupon the suspended s o l i d r a p i d l y became yellow.  A f t e r 5 minutes of  a d d i t i o n a l s t i r r i n g , the product was c o l l e c t e d by s u c t i o n f i l t r a t i o n . The y i e l d of 2,3-dicarbomethoxy-l,4-benzoquinone (145) was 1.15 g (97%, o v e r a l l y i e l d was 16.5% from dicyanohydroquinone), obtained as a yellow s o l i d , mp 153 - 155° a f t e r r e c r y s t a l l i z a t i o n from benzene - petroleum ether ( l i t ? 1 5 5 - 157°). 7  4aB,8a8-Dicarbomethoxy-6,7-dimethyl-4a,5,8,8a-tetrahydro-1,4naphthoquinone (100)?  3  A s o l u t i o n of 1.15 g (5.1 mmol) of quinone 145, 1 g (12 mmol) of 2,3-dimethyl-l,3-butadiene and 50 ml of anhydrous methanol was r e f l u x e d f o r 2.5 hours and then s t i r r e d at room temperature f o r 4 more hours.  Evaporation of solvent y i e l d e d a yellow o i l which was  chromatographed on 75 g of .nuetral Alumina using e t h y l acetate as the e l u t i n g solvent.  Two components were obtained; the f i r s t to be  eluted consisted of 530 mg of crude adduct 100.  Recrystallization  from benzene-petroleum ether (68°) y i e l d e d 400 mg (26%) of 100 as c o l o r l e s s c r y s t a l s , mp 132 - 133.5° ( l i t ? 1 3 2 - 135°). 3  c h a r a c t e r i s t i c s were:  i r (KBr) 5.79, 5.91 (C=0), 6.21  Spectral (C=C)y;  - i66 nmr ( C D C l ^ T 3.27 ( s , 2,, 7.28  (br s, 4, C  methyls);  c  and C  Q  and  v i n y l s ) , 6.23 ( s , 6, methoxy methyls),  methylenes), 8.38 (br s, 6, C. and C,  uv max (methanol) 229 (e 7900), a f e a t u r e l e s s s l o p i n g  absorption from 300 - 350 nm (e at 340 = 147).  The second component  (490 mg) was i d e n t i f i e d as crude 2,3-dicarbomethoxy-5,8-dihydro-6,7dimethyl-1,4-naphthoquinol (146) :  nmr ( C D C l ^ T 0.73 ( s , 2, disappears  on adding D2O, OH), 6.1 ( s , 6, ester methyls), 6.77 ( s , 4, C,- and Cg methylenes), 8.22 ( s , 6, v i n y l methyls). R e c r y s t a l l i z a t i o n from ethanol - petroleum ether (68°) gave pure 146 as c o l o r l e s s needles, mp 187 - 188° ( l i t 1 8 9 - 190°). 6 3  P h o t o l y s i s of Adduct 100. A s o l u t i o n of 190 mg (0.62 mmol) of 100 i n 50 ml of benzene was i r r a d i a t e d f o r 5 hours, a f t e r which the uv spectrum of the r e a c t i o n mixture remained unchanged.  Evaporation of solvent i n vacuo  r e s u l t e d i n a residue which showed two main components on t i c ( S i l i c a Gel; Gel  40% e t h y l acetate-benzene). Column chromatography on S i l i c a (40% e t h y l acetate-benzene) gave 110 mg (58%) of ene-dione  148 and 15 mg (8%) of enone a l c o h o l 147, both as c o l o r l e s s s o l i d s . In a second experiment, 80 mg (0.26 mmol) of 100 i n 40 ml of benzene were i r r a d i a t e d f o r a shorter length of time (2.5 h r s . ) .  Workup  as above gave 28 mg (35%) of 148 and 24 mg (30%) of 147. These s t r u c t u r e s were assigned on the b a s i s of the f o l l o w i n g s p e c t r a l data:  r  3  for 148, 1,6-dicarbomethoxy-8,9-dimethyltricyclo.14.4.0.0 7-ene-2,5-dione: (CDC1 3 )T 3.51  i r (KBr) 5.58, 5.72, 5.78, 5.86  (m, 1, C  7  v i n y l ) , 6.22 and 6.26  Cg carbomethoxy methyls), 6.2 - 6.4 1, J=5Hz, 16Hz, C  4  gi ' J dec-  (C=0)y;  nmr  (each s, 6, Cj and  (m, I , C^ methine), 7.32  exo-methylene), 7.53  (dd, 1, J=4Hz, 16Hz,  (dd, C^  endo-methylene), 7.76 (d, 1, J=14Hz, C methylene) 8.12 (d, 3, J=lHz, C. v i n y l methyl), 8.14 (d, 1, J=14Hz, C,„ methylene), 8.75 o • lU 1Q  (s, 3, Cg methyl);  the chemical s h i f t s of the C^ exo and endo-  protons and the C^Q methylenes were c a l c u l a t e d ? 300 (e 165), sh 313 nm (e 134); 306.  Recrystallization  Uv max  2  mass spectrum (70 eV) m/e  from benzene-petroleum  (methanol) parent  ether (68°) gave an  a n a l y t i c a l l y pure sample, mp 96.5 - 97°. Anal. 63.03;  H,  Calcd. f o r C.,H 0,: lo l o o 10  C, 62.74;  H, 5.92.  Found:  C,  5.89.  [  5 o"|  for 147, 1,6-dicarbomethoxy-8,9-dimethyl-5-hydroxytricyclo [4.4.0.0 ' J deca-3,7-diene-2-one: (CDC13)T  4.17  3.41  i r (KBr) 2.92  (d, 1, J=10Hz, C  (m, 1, C^ v i n y l ) , 6.27  4  (OH), 5.80, 5.90 .(C=0)y;  v i n y l ) , 3.78  and C  (d, 3, J=1.5Hz, C 4  g  methyl), 8.86  (br s, 2,  ( s , 3, C  v i n y l resonance s h i f t s were c a l c u l a t e d  g  parent 306.  Recrystallization  methylenes),  methyl), the C ;  241 (e 3630), long s l o p i n g t a i l (e at 325 =* 50); (70 eV) m/e  vinyl),  3  ( s , 6, carbomethoxy methyls), 7.22  (s, 1, disappears on adding D2O, OH), 8.03 8.19  (d, 1, J=10Hz, C  nmr  uv max  3  (methanol)  mass spectrum  from benzene-petroleum  ether  - 168 (68°) gave an a n a l y t i c a l l y pure sample, mp 158.5 - 159? Anal. 62.85;  Calcd. f o r C..H 0.: lo l o o 1Q  C, 62.74;  H, 5.92. Foung:  C,  H, 5.89.  Thermolysis of Ene-Dione 148. Product 148 (20 mg, 0.065 mmol) was placed i n a sealed ampoule and heated f o r 3.5 hours at 190°. The golden product was d i s s o l v e d i n chloroform and chromatographed through a short column of alumina (chloroform), g i v i n g 19 mg of a pale yellow o i l .  Chromatography  on S i l i c a Gel (40% e t h y l acetate-benzene) gave 10 mg (50%) of enone a l c o h o l 147, whose i r and nmr spectra were i d e n t i c a l to those of m a t e r i a l obtained from p h o t o l y s i s of 100 i n benzene.  P h o t o l y s i s of Adduct 100 i n t e r t - B u t a n o l . A s o l u t i o n of 106 mg (0.35 mmol) of 100 i n 25 ml of 5% benzenet e r t - b u t a n o l was i r r a d i a t e d f o r 5 hours.  Evaporation of solvent  followed by column chromatography (40% e t h y l acetate-benzene, S i l i c a Gel)  gave two components.  The f i r s t f r a c t i o n , 48 mg, proved to be  a complex mixture of many products ( t i c , i r and nmr), a r i s i n g p o s s i b l y from a b s t r a c t i o n of a carbomethoxy methyl hydrogen atom and was not  investigated further.  The second component, 41 mg, was i d e n t i f i e d  as enone a l c o h o l 147 on the b a s i s of i t s melting point and s p e c t r a l data. This represented a y i e l d of 39%.  *  -  169  -  1  .  Synthesis of Duroquinone (154). Duroquinone was prepared i n three steps f o l l o w i n g the procedure reported by  A.  Smith  69  Dinitrodurene. A s o l u t i o n of 13.4 g (0.1 mole) of durene ( f r e s h l y r e c r y s t a l l i z e d  from methanol) i n 100 ml of chloroform was added to 75 ml of concentrated s u l p h u r i c a c i d contained i n a 1 l i t r e Erlenmeyer f l a s k .  After  c o o l i n g the mixture below 10° C using an i c e - s a l t - w a t e r s l u s h , 16 g (11 ml) of fuming n i t r i c acid were added dropwise w i t h s t i r r i n g over a 20 minute p e r i o d .  As soon as the a d d i t i o n was  complete,  the r e a c t i o n mixture was t r a n s f e r r e d to a separatory funnel and the lower acid l a y e r was drawn o f f . The chloroform l a y e r was added to 500 ml of saturated sodium bicarbonate s o l u t i o n , a f t e r which the l a y e r s were separated.  The organic phase was washed w i t h water,  d r i e d over calcium c h l o r i d e , f i l t e r e d and concentrated i n vacuo. When c r y s t a l s began to form, 150 ml of hot ethanol were added to the mixture, which was then c h i l l e d i n the r e f r i g e r a t o r . was f i l t e r e d and washed twice w i t h cold ethanol.  B.  solid  The mother l i q u o r  was concentrated, and a second crop of c r y s t a l s was T o t a l y i e l d was  The  collected.  18.65 g (83%).  Reduction of d i n i t r o d u r e n e . The dinitrodurene obtained above (18.65 g, 0.083 mole) was  d i s s o l v e d i n 250 ml of g l a c i a l a c e t i c a c i d i n a 2 l i t r e f l a s k , and  - 170 the s o l u t i o n was heated to b o i l i n g .  Meanwhile a s o l u t i o n of 175 g  of stannous c h l o r i d e i n 200 ml cone h y d r o c h l o r i c a c i d was a l s o heated to b o i l i n g .  The heat was removed, and the stannous c h l o r i d e  s o l u t i o n was poured very c a r e f u l l y i n t o the dinitrodurene s o l u t i o n over 10 minutes.  A vigorous r e a c t i o n took place.  After s t i r r i n g  for 15 minutes the mixture was cooled and the s o l i d which p r e c i p i t a t e d was f i l t e r e d and washed w i t h ethanol, ether, and then was d r i e d . Y i e l d was q u a n t i t a t i v e (33 g) and consisted of ^ ( C H ^  (NH *HC1) 2  •SnCl.. 4 C.  Duroquinone. A s o l u t i o n of 193 g of f e r r i c c h l o r i d e hexahydrate i n 125 ml  water and 8 ml cone h y d r o c h l o r i c a c i d was prepared i n a 500 ml Erlenmeyer f l a s k , and to i t was added, w i t h s t i r r i n g , the t i n compound prepared above, which r e s u l t e d i n a t h i c k yellow suspension. s t i r r i n g overnight, the mixture was f i l t e r e d , and the s o l i d a i r d r i e d f o r an hour.  After was  A f t e r t h i s , the s t i l l s l i g h t l y damp s o l i d  was d i s s o l v e d i n 400 ml of petroleum ether (68°) and the r e s i d u a l water was removed w i t h calcium c h l o r i d e .  A f t e r f i l t r a t i o n , the b r i g h t  yellow s o l u t i o n was evaporated to dryness.  The crude yellow s o l i d  was r e c r y s t a l l i z e d from petroleum ether (68°) to give b r i l l i a n t yellow needles of duroquinone (154); mp 111 - 112°. 10.2 g (62% from durene).  «  Yield  was  I  - 171 2,3, 4aS,56,88,8a3-Hexamethyl-4a,5,8,8a-tetrahydro-1,4-naphthoquinone  (101).  A mixture of 1.6 g (9.8 mmol) of duroquinone (154), 2 g (24.4 mmol) of f r e s h l y d i s t i l l e d trans,trans-2,4-hexadiene, and a few c r y s t a l s of hydroquinone was heated i n a sealed Pyrex tube at 190° f o r 20 hours. The dark r e a c t i o n mixture was dissolved i n acetone and evaporated i n vacuo, r e s u l t i n g i n a dark brown gum.  Extraction with refluxing  methanol, followed by evaporation of solvent and preparative glpc (column A, 160°, 160 ml/min) y i e l d e d 120 mg (5%) of adduct 101, which upon r e c r y s t a l l i z a t i o n from petroleum ether (30 - 60°) formed pale yellow needles, mp 103 - 104°, and e x h i b i t e d the f o l l o w i n g p r o p e r t i e s : uv max (methanol) 251 (e 8700), 340 nm (e 70);  nmr ( C C l ^ T 4.58 ( s , 2, v i n y l s ) , 7.17 (q, 2,. J=7Hz,  6.13 (C=C)y; C  c  -  i r (KBr) 5.99 (C=0),  and C methines), 8.07 ( s , 6, C. and C„ methyls), 8.93 ( s , 6, C, o . 2 5 ita Q  >  and C  Q  oa  methyls), 9.12 (d, 6, J=7Hz, C ^  c  and C methyls); mass spectrum J  0  O  (70 eV) m/e parent 246. Anal.  Calcd.' f o r C.,H .0_:- C, 78.01; l o 22 2 o  H, 9.00. Found:  C, 77.75;  H, 9.11.  P h o t o l y s i s of Adduct 101. A s o l u t i o n of 110 mg (0.49 mmol) of 101 i n 50 ml of benzene was placed i n a quartz tube and i r r a d i a t e d w i t h l i g h t of wavelength >_ 340 nm.  The r e a c t i o n was monitored by glpc (column A, 160°, 160 ml/min),  which showed the formation of two new products at the expense of 101.  - 172 A f t e r 3 hours, 101 had completely reacted, and the two products 155 and 156 remained i n a r a t i o of 1:2 traces).  (determined by weighing glpc  Evaporation of solvent followed by column  chromatography  (10 g S i l i c a G e l , 10% e t h y l acetate/benzene) afforded 62 mg 156 and 27 mg  (56%) of  (24.5%) of 155 whose s t r u c t u r e s were assigned on the  b a s i s of the f o l l o w i n g p r o p e r t i e s :  f o r compound 156, 1,3,4,6,7,10-hexamethyltricyclo [4.4.0.0 ' ] dec-8-ene 3  -2,5-dione:  colorless o i l ;  (neat) 5.66, 5.85 5.5Hz, C 7.30  o  Q  (C=0)y;  v i n y l ) , 4.49  (q, 1, J=7.5Hz, C  (s, 3, methyl), 8.98 9.02  nmr  (CDCl-)x 4.03  (dd, 1, J  n  4  (methanol) 290 nm (e 68); i r  ?  (dd, 1, J  3  =10Hz, J  D  o , y  =  Q  o , /  =10Hz, J =1.5Hz, C„ v i n y l ) , 9,o 9,/ 9 Q  n  methine), 7.82  (d, 3, J=7.5Hz, C  (d, 3, J=7.5Hz, C  methyl).  uv max  10  methyl), 9.03  (m, 1, C 4  ?  methine),  methyl), 9.01  8.98  ( s , 3, methyl),  ( s , 3, methyl), 9.09  ( s , 3,  I r r a d i a t i o n at T7.30 leads to the c o l l a p s e of the doublet  at T8.98 to a s i n g l e t .  I r r a d i a t i o n at T7.82 leads to the c o l l a p s e  of the doublet at X9.02 to a s i n g l e t , and to s i m p l i f i c a t i o n of the v i n y l s i g n a l s to an AB system w i t h a mutual coupling constant of 10Hz.  Mass spectrum (70 eV) m/e  parent 246.  D i s t i l l a t i o n (Kugelrohr)  at 0.005 t o r r and 65°C y i e l d e d an a n a l y t i c a l l y pure Anal. 78.30;  H,  Calcd. f o r C.,H „0 : l o // / o  o  C, 78.01;  H, 9.00.  sample. Found:  C,  9.20.  T  5 9l  f o r compound 155, 1,3,4,6,7,10-hexamethyl-5-hydroxytricyclo 4.4.0.0 ' deca-3,7-diene-2-one:  colorless crystalline s o l i d ;  mp 156.5 -  157°  - 173 (petroleum ether 68 ); uv max (methanol) 247 (e 5700), broad f e a t u r e l e s s absorption (e 175 a t 340 nm); (C=0)y;  nmr (CC1 )T 4.15 (m, 1, v i n y l ) , 7.45 (dd, 1, J 4  Jg ^=3Hz,  1 Q  methine), 8.16 ( s , 3, C  methyls), 9.20 ( s , 3, ^  7  78.01;  g=3Hz,  3  methyl), 8.25 (br s, 6,  methyl), 9.29 ( d , 3, J=7Hz, C  methyl), 9.34 ( s , 3, C, methyl); o 246. Anal.  g  methine), 7.67 ( s , 1, disappears on adding V^O, OH),  7.79 (m, 1, C and C  i r (KBr) 2.88 (OH), 6.05  1Q  mass spectrum (70 eV) m/e parent  Calcd. f o r C^H.^O.: io zz z  C, 78.01;  H, 9.00.  Found:  C,  H, 9.01.  Thermolysis of Ene-Dione 156. Ene-dione 156 (21 mg, 0.09 mmol) was placed i n a sealed ampoule and thermolyzed f o r 21 hours a t 195°. The crude product was taken up i n chloroform and chromatographed on 5 g of S i l i c a Gel using chloroform as the e l u t i n g solvent.  I n t h i s way, a s l i g h t l y yellow  o i l was obtained, which was d i s t i l l e d at 70° and 0.005 t o r r to give 13 mg (63%) of 2,3,4aB,5,83,8a3-hexamethyl-4a,7,8,8a-tetrahydro1,4-naphthoquinone (157) as a c o l o r l e s s o i l . features of 157 were as f o l l o w s : 352 nm (e 70);  Distinguishing spectral  uv max (methanol) 254 (e 11,000),  i r (neat) 5.98 (C=0)u;  nmr ( C C 1 ) T 4.50 (m, 1, v i n y l ) ; 4  8.07 (s, 6, v i n y l methyls), 8.12 (br s, 3, v i n y l methyl), 8.40 (centre of broad m u l t i p l e t , 1, Cg methine), 8.75 - 9.25 (broad m u l t i p l e t , 2, C  7  methylenes), 8.84 ( s , 3,  methyl), 9.05 ( s , 3, C  g a  methyl),  - 174 9.37  (d, 3, J=6Hz, C„ methyl);  mass spectrum (70 eV) m/e  parent  246.  o  Anal. 78.16;  Calcd. f o r C ,H„„0 : lo 22 2 1  H,  C, 78.01;  o  H, 9.00.  Found:  C,  9.20.  2,3,4aB,5a,8a,8a8-Hexamethyl-4a,5,8,8a-tetrahydro-1,4-naphthoquinone (102). A mixture of 1.6 g (9.8 mmol) of duroquinone (154), 2 g (0.024 mole) of trans,trans-2,4-hexadiene  and a few c r y s t a l s of hydroquinone  was placed i n a sealed Pyrex tube and heated at 140° f o r 40 hours.  The  mixture was cooled and then extracted w i t h hot petroleum ether (68 ). A f t e r f i l t r a t i o n and concentration, the s o l u t i o n was c h i l l e d i n the f r e e z e r whereupon a crop of unreacted 154 p r e c i p i t a t e d .  After a  second f i l t r a t i o n and f u r t h e r concentration, the s o l u t i o n was  again  c h i l l e d whereupon 400 mg of yellow s o l i d , mp 40 - 42°, were deposited. This s o l i d was c o l l e c t e d by s u c t i o n f i l t r a t i o n and r e c r y s t a l l i z e d twice more from a small amount of petroleum ether (68°). way,  246 mg  (10%) of 102 could be i s o l a t e d .  mp o f 47 - 50  In t h i s  This m a t e r i a l had a  and was found to be s u i t a b l e f o r p h o t o l y s i s .  An  a n a l y t i c a l sample could be obtained by preparative glpc (column A, 170°,  150 ml/min) followed by r e c r y s t a l l i z a t i o n from petroleum  ether (68°). 57 - 58°. uv max  The f o l l o w i n g s p e c t r a l data support the s t r u c t u r e of 102:  (benzene) 350 nm (e 83);  (CCl^)T 4.57 8.10  Adduct 102 thus obtained was pale yellow needles, mp  ( s , 6, C  i r (KBr) 5.94,  ( s , 2, v i n y l H), 7.85 2  and C  3  methyls), 8.81  6.00  (q, 2, J=7Hz, C ( s , 6, C^  a  5  (C=0)y; and C  and C  g a  g  nmr  methines),  methyls).  - 175 9.02 (d, 6, J=7Hz, C  c  J  and C  methyls);  0  O  mass spectrum (70 eV)  m/e parent 246. Anal. 77.96;  Calcd. f o r C,,H 0 : lo 2.1 2 oo  o  C, 78.01;  H, 9.00. Found:  C,  H, 8.86.  P h o t o l y s i s of Adduct 102 i n Benzene. Adduct 102 (130 mg, 0.53 mmol) i n 25 ml of benzene was placed i n a quartz tube and i r r a d i a t e d w i t h 340 nm l i g h t .  The r e a c t i o n was  monitored by a n a l y t i c a l glpc (column A, 170°, 150 ml/min) which showed the formation of two new products;  one product,  subsequently  i d e n t i f i e d to be oxetane 160, was observed to buildup r a p i d l y u n t i l i t reached a constant r a t i o w i t h 102 of about 1:1.9 (weight of glpc t r a c e s ) .  The other product formed more s l o w l y , at the expense  of both 102 and 160, u n t i l a f t e r 18 hours of i r r a d i a t i o n , i t was the only detectable product.  Evaporation of the solvent y i e l d e d  110 mg of pale yellow s e m i - s o l i d , which was r e c r y s t a l l i z e d from petroleum ether (68°) to give 93 mg of c o l o r l e s s c r y s t a l s .  This  represented a y i e l d of approximately 95%, a f t e r c o n s i d e r a t i o n of the m a t e r i a l withdrawn during the course of the r e a c t i o n to monitor i t s progress.  An a d d i t i o n a l r e c r y s t a l l i z a t i o n from petroleum ether  (68°) y i e l d e d 80 mg of a n a l y t i c a l l y pure m a t e r i a l which was i d e n t i f i e d as l,3,4,6,7,10-hexamethyltetracyclo[4.4.0.0  .0 ' J deca-2,5-  dione (161) on the b a s i s of the f o l l o w i n g p r o p e r t i e s : mp 144 - 146°; i r (CCI.) 5.68, 5.75 (C=0)y;  nmr (CCl.)t 7.40 (q, 2, J=7Hz, C and 7  - 176 -  C,_ methines), 7.60 ( s , 2, C and C. methines), 8.97 ( s , 6, C. and C, 10 o 9 1 6 0  methyls), 9.07 (s, 6, C methyls);  3  and  methyls), 9.33 (d, 6, J=7Hz, C  7  and C  1 Q  uv max (methanol) 227 (e 333), 299 (e 40), 315 nm (e 33);  mass spectrum (70 eV) m/e parent 246. Anal.  77.82;  Calcd. f o r C.-H.-O.: l o 22 2  C, 78.01;  H, 9.00. Found:  C,  H, 9.12.  u t i Oxetane o n of 246 mg (1.0 mmol) of 102 i n 40 ml of benzene was I s o l aA t i os no l of 160. i r r a d i a t e d as u s u a l , the r e a c t i o n being followed by glpc (column A, 170° 150 ml/min).  The p h o t o l y s i s was i n t e r r u p t e d a f t e r 4 hours, at which time  the r a t i o of products was 160:102:161 = 1:1.9:1.2.  A f t e r evaporation of  s o l v e n t , the residue was subjected to p r e p a r a t i v e glpc (column A, 170° 150 ml/min) from which was i s o l a t e d 14 mg 160, 46 mg of unreacted 102 and 16 mg of cage compound 161.  R e c r y s t a l l i z a t i o n of 160 from petroleum ether (30 -  60°) y i e l d e d c o l o r l e s s c r y s t a l s , mp 59.5 - 60° deduced to be 2,3,5,6,9,10hexamethyl-ll-oxatetracyclo |j6.2.1.0^ ^.0^'''"^] undeca-2-ene-4-one (160) ,  from the f o l l o w i n g s p e c t r a l evidence:  i r (KBr) 6.04 (C=0)y;  nmr ( C C l ^ T  5.64 (d, 1, J=4Hz, C methine), 7.40 (d, 1, J=4Hz, C_. methine), 7.78 (q, o / 1, J=7Hz, C or C methine), 8.03 (br s, 3, C methyl), 8.33 (br s, 3, C D  &  g  2  3  methyl), 8.35 (q, 1, J=7.5Hz, C, or C„ methine), 8.97 ( s , 3, C or C methyl) o 9 _> |0 9.01 (d, 3, J=7Hz, Cg or C methyl), 9.30 ( s , 3, C or C methyl), 9.46 c  g  5  (d, 3, J=7.5Hz, C. or C methyl); o 9 n  (e 240); Anal. H, 9.05.  lft  1 Q  uv max (methanol) 266 (e 6100), 325 nm  mass spectrum (70 eV) m/e parent 246. Calcd. f o r C.,H..0 : l b 22 2 o  C, 78.01;  H, 9.00. Found:  C, 78.18  - 177 P h o t o l y s i s of Oxetane _160. A s o l u t i o n of 11.5 mg (0.047 mmol) of 160 i n 4 ml of benzene was i r r a d i a t e d as u s u a l , the r e a c t i o n being monitored by glpc (column A, 170° 150 ml/min) which showed r a p i d buildup of 102 ( a f t e r h hour, r a t i o of 160; 102 = 1:1.9).  Then a t longer i r r a d i a t i o n times, cage compound 161 formed  at t h e expense of both 160 and 102 u n t i l a f t e r 12 hours i t remained as the only product.  The m a t e r i a l i s o l a t e d was i d e n t i c a l to that obtained  from p h o t o l y s i s of 102 i n benzene. P h o t o l y s i s of 102 i n t e r t - B u t a n o l . A s o l u t i o n of 10 mg (0.04 mmol) of 102 i n 3 ml of t e r t - b u t a n o l was irradiated.  Glpc (column A, 170° 150 ml/min) showed gradual formation of  cage compound 161;  however, no oxetane 160 was observed, and no other  product could be detected. Thermolysis of Adduct 102. Compound 102 (10 mg, 0.04 mmol) was placed i n a sealed ampoule and heated at 190° f o r 9 hours a f t e r which time, the dark r e a c t i o n mixture was d i s s o l v e d i n chloroform and analyzed .by glpc (column A, 170° 150 ml/min). This showed extensive decomposition to duroquinone and other products had occurred.  However, the formation of compound 101 was confirmed by comparison  of r e t e n t i o n times, and by c o i n j e c t i o n .  The r a t i o of 102:101 was determined  to be 1:3 (weight of glpc t r a c e s ) . 4aB,8aB-Dicyano-5a,8a-dimethyl-4a,5,8,8a-tetrahydro-1,4-naphthoquinone  (103).  To a s o l u t i o n of 1 g (6.5 mmol) of 2,3-dicyano-l,4-benzoquinone (135) i n 20 ml of benzene-ethanol (9:1 by volume) was added 1 g (12 mmol) of trans,trans-2,4-hexadiene. temperature f o r 3 hours.  The mixture was allowed t o stand at room Evaporation of solvent and excess diene y i e l d e d  - 178 1.2 g of s o l i d , which on r e c r y s t a l l i z a t i o n from methanol, gave 800 mg (52%) of 103 as pale yellow c r y s t a l s , mp 152 - 153°. c h a r a c t e r i s t i c s were as f o l l o w s : (C=0), 6.23 (C=C)y;  Spectral  i r (KBr) 4.43 (C=N), 5.79 and 5.90  nmr (CDCl )x 3.01 ( s , 2, C 3  and C  £  3  vinyls),  4.32 ( s , 2, Cg and C  7  v i n y l s ) , 6.85 (q, 2, J=7Hz, C,. and Cg methines),  8.69 (d, 6, J=7Hz, C  c  and C methyls);  352 nm (e 64);  uv max (methanol) 240 (e 6200),  Q  j  o  mass spectrum (70 eV) m/e parent 240. Another  r e c r y s t a l l i z a t i o n (methanol) y i e l d e d an a n a l y t i c a l sample of 103, mp 155 - 156°. Anal. Found:  Calcd. f o r 4  C, 70.29;  C  1  H  N 1 2  2°2  :  C  '  6 9  *  9 9 ;  H  » - '> 5  03  N  »  H.66.  H, 5.25; N, 11.39.  P h o t o l y s i s of 103 i n Benzene. A s o l u t i o n of 412 mg (1.7 mmol) of 103 i n 200 ml of benzene was i r r a d i a t e d as u s u a l , the r e a c t i o n being monitored by uv spectroscopy which showed complete disappearance of the 352 nm peak and a buildup of a new absorption at 330 nm a f t e r 5 hours.  Evaporation of solvent  followed by column chromatography ( S i l i c a G e l ;  30% e t h y l acetate-  benzene) y i e l d e d 253 mg of c o l o r l e s s o i l which c r y s t a l l i z e d on standing. R e c r y s t a l l i z a t i o n from ether-petroleum ether (68°) gave 215 mg (52%) of c o l o r l e s s c r y s t a l s , mp 137.5 - 139 . On the b a s i s of the f o l l o w i n g s p e c t r a l data, the compound was i d e n t i f i e d as 5,10-dicyano-6,9-dimethyl11-oxatetracyclo {6.2.1.0 .0 °Jundec-2-ehe-4-one (169) : 1,7  4.43 (CSN) 5.93 (C=0)u;  i r (KBr)  5,1  nmr (CDC± )T 2.46 (d, 1, J=10Hz, C 3  £  vinyl),  3.73 (d, 1, J=10Hz, C_ v i n y l ) , 5.23 (d, 1, J=4Hz, C methine), 6.83 fi  179  -  -  (d, 1, J=4Hz, C, methine), 7.11 (q, 1, J=7Hz, C- or C_ methine), /  7.35  b  (q, I , J=7.5Hz, C, or C b  0  y  methine), 8.60 (d, 3, J=7Hz, C, o r C  y  b  methyl), 9.05 (d, 3, J=7.5Hz,  or Cg methyl).  N  y  I r r a d i a t i o n of the  doublet at T 9 . 0 5 leads to c o l l a p s e of the quartet at T 7 . 3 5 to a I r r a d i a t i o n of the doublet at T 5 . 2 3 causes the doublet at  singlet. T6.83  I r r a d i a t i o n at T 3 . 7 3 causes the  to c o l l a p s e to a s i n g l e t .  doublet at T 2 . 4 6 to c o l l a p s e to a s i n g l e t . (e 3200), 330 nm (e 66); Anal. Found:  Calcd. f o r 4  C, 69.93;  C  1  Uv max (methanol) 258  mass spectrum (70 eV) m/e parent 240. H  N 1 2  2°2  :  C  '  6 9 , 9 9  »  H  » 5  0 3  5  N  » H.66.  H, 5.10; N, 11.60.  P h o t o l y s i s of 103 i n t e r t - B u t a n o l . A s o l u t i o n of 97 mg (0.4 mmol) of 103 i n 50 ml of 10% benzenet e r t - b u t a n o l was i r r a d i a t e d i n the usual way, the r e a c t i o n being followed by t i c and uv. A f t e r 2 hours, the r e a c t i o n was complete; evaporation of solvent followed by chromatography  ( S i l i c a Gel, 30%  e t h y l acetate-benzene) y i e l d e d 60 mg (62%) of oxetane 169, i d e n t i c a l i n a l l regards w i t h the compound obtained from the benzene p h o t o l y s i s .  Attempted P h o t o l y s i s of Oxetane 169 i n Benzene. A s o l u t i o n of 55 mg (0.23 mmol) of 169 i n 25 ml of benzene was i r r a d i a t e d w i t h l i g h t f i l t e r e d through a Pyrex f i l t e r ( t r a n s m i t t i n g A >^ 290 nm). T i c and uv a n a l y s i s of a l i q u o t s showed no r e a c t i o n had occurred a f t e r 10 hours of i r r a d i a t i o n . q u a n t i t a t i v e l y recovered.  S t a r t i n g m a t e r i a l was  - 180 Attempted P h o t o l y s i s of Oxetane 169 i n t e r t - B u t a n o l . A s o l u t i o n of 47 mg (0.2 mmol) of 169 i n 30 ml of 10% benzenet e r t - b u t a n o l was i r r a d i a t e d f o r 22 hours. products were detected;  oxetane 169 was  A f t e r t h i s time no recovered.  new  - 181 BIBLIOGRAPHY 1.  R.O. Kan, "Organic Photochemistry", McGraw-Hill Book Co., New York, N.Y. 1966.  2.  S.J. C r i s t o l and R.L. S n e l l , J . Amer. Chem. S o c , 80, 1951 (1958).  3.  G. Buchi and I.M. Goldman, i b i d . , 79, 4741 (1957).  4.  P.E. Eaton and T.W. Cole, J r . , i b i d . , 86, 962, 3157 (1964).  5.  W.L. D i l l i n g , Chem. Rev., 66, 373 (1966).  6.  J . I p a k t s c h i , Tetrahedron Lett., 3179 (1970).  7. H.E. Zimmerman, Angew. Chem. I n t . Ed. E n g l . , 8^ 1 (1969). 8.  A. Padwa, Tetrahedron L e t t . , 3465 (1964);  C. W a l l i n g and V. Kurkov,  J . Amer. Chem. S o c , 88, 4727 (1966). 9. 10.  P.J. Wagner, Acc. Chem. Res.,  168 (1971).  R.C. Cookson, E. Crundwell, R.R. H i l l and J . Hudec, J . Chem. S o c , 3062 (1964). .  11.  P.E. Eaton and S.A. C e r e f i c e , Chem. Commun., 1494 (1970).  12.  J.R. S c h e f f e r , J . T r o t t e r , R.A. Wostradowski, C.S. Gibbons and K.S. Bhandari, J . Amer. Chem. S o c , 93, 3813 (1971).  13.  The n — TT nature of the absorption was v e r i f i e d by i t s progressive blue s h i f t i n solvents of i n c r e a s i n g p o l a r i t y : ether, 367 nm; 362 nm;  14.  e t h y l acetate, 365 nm;  hexane, 370 nm;  acetone, 364 nm;  acetonitrile,  methanol, 358 nm.  C.S. Gibbons and J . T r o t t e r , J . Chem. S o c , P e r k i n Trans. I I , 737 (1972).  -  15.  J.R. S c h e f f e r , K.S. B h a n d a r i , R.E. G a y l e r and R.H. Wiekenkainp,  16.  182 -  J . Amer. Chem. Soc. , 94., 285 (1972).  T.T. T i d w e l l , i b i d ,  92!, 1448 (1970).  17a. N.H. W e r s t i u k and R. T a i l l e f e r ,  Can. J . Chem., 48, 3966 (1970); b)  S. B a n e r j e e and N.H. W e r s t i u k , i b i d , 18.  53, 1099 (1975).  R.B. Woodward and R. Hoffmann, "The C o n s e r v a t i o n o f O r b i t a l Symmetry", Academic P r e s s , New York, N.Y. 1970.  19a. R.L. C a r g i l l , B.M. Gimarc, D.M. Pond, T.Y. K i n g , A.B. Sears and M.R. W i l l c o t t , J . Amer. Chem. Soc., 92, 3809 (1970); For r e l a t e d work and examples,  see P.S. Mariano  and D. Watson,  J . Org. Chem., 39, 2774 (1974) and r e f e r e n c e s c i t e d 20.  While these r e a c t i o n s l i k e l y another p o s s i b i l i t y  b)  therein.  involve b i r a d i c a l intermediates,  cannot be d i s c o u n t e d a t p r e s e n t ;  a c o n c e r t e d mechanism under t h e i n f l u e n c e o f s u b j a c e n t control.  namely, orbital  See J.A. Berson, A c c . Chem. Res. , 5_, 406 (1972);  J.A.  Berson, i b i d , J_, 152 (1968). 21.  U. Klinsmann,  J . G a u t h i e r , K. S c h a f f n e r , M. P a s t e r n a k and B. Fuchs,  H e l v . Chim. A c t a . , 55, 2643 22.  H. Zimmerman  7  proposed  (1972).  the f o r m a t i o n o f a s o l v a t e d  zwitterion  i n t h e p h o t o c h e m i s t r y o f c y c l o h e x a d i e n o h e s , as shown below. The major d i f f e r e n c e , however, between z w i t t e r i o n ji and 35_ i s t h a t jL forms a c o n j u g a t e d system which 35.  i s not t h e case i n  - 183 -  0  0'  Ph  Ph P h  Ph  oe  O  Ph Ph  23.  R.E. G a y l e r , Ph. D. T h e s i s , U n i v e r s i t y o f B.C. 1973.  24.  G. S. Hammond, J . Amer. Chem. Soc. , 77, 334 (1955).  25.  J.R. S c h e f f e r , K.S. B h a n d a r i , R.E. G a y l e r and R.A.  x  Wostradowski,  J . Amer. Chem. S o c , 97, 2178 (1975). .26.  F.P.  27.  As measured on D r e i d i n g models.  28.  E.L. E l i e l ,  L o s s i n g , Can. J . Chem., 50, 3973 (1972).  " S t e r e o c h e m i s t r y o f Carbon Compounds",  McGraw-Hill  I n c . , New York, N.Y. 1962. p. 205. 29.  H. M.R. Hoffman, Angew. Chem. I n t . Ed. E n g l . , iB, 556 (1969).  30.  J . T r o t t e r and C A . Bear, J . Chem. Soc. , P e r k i n T r a n s . I I , 330 (1974).  31.  Such a s h i f t 303 (1970).  f i n d s analogy i n t h e work o f S. F a r i d , Chem. Commun.  - 184 32.  For a p o s s i b l e example, see A. Padwa and W. Eisenhardt, J . Amer. Chem. Soc., 93, 1400 (1971).  I n t h i s case, however, i t i s a *  n e g a t i v e l y charged oxygen atom and not an n - IT excited s t a t e which i s r e s p o n s i b l e f o r the B-hydrogen a b s t r a c t i o n .  For other  p o s s i b l e examples see E.J. Baum, L.D. Hess, J.R. Wyatt and J.N. P i t t s , J r . , i b i d , 91, 2461 (1969); Vesley, i b i d , 85, 3776 (1963); 9_2, 7467 (1970);  P.A. Leermakers and G.F.  N.J. Turro and T.J. Lee, i b i d ,  P. G u l l , H. Wehrli and 0. Jeger, Helv. Chem.  Acta., 54, 2158 (1971). 33.  R.A. Cormier, W.L. Schreiber and W.C. Agosta, Chem. Commun., 729 (1972);  J . Amer. Chem. Soc. , 9_5, 4873 (1973).  34.  P.S. S k e l l and R.G. Doerr, J . Amer. Chem. Soc. , 89, 4688 (1967).  35.  J.R. Scheffer and K.S. Bhandari, unpublished r e s u l t s .  36.  W. Herz and M.G. N a i r , J . Amer. Chem. Soc., 89, 5474 (1967); J.A. Turner, V. I y e r , R.S. McEwen and W. Herz, J . Org. Chem., 39, 117 (1974).  37.  P.J. Wagner and G.S. Hammond, Advan. Photochem., _5, 21 (1968).  38.  D. B e l l u s , D.R. Kearns and K. Schaffner, Helv. Chim. Acta., 52, 971 (1969).  39.  T. Kobayashi, M. Kurono, H. Sato and K. Nakanishi, J . Amer. Chem. Soc. , 94, 2863 (1972).  40.  S.Wolff, W.L. Schreiber, A.B. Smith, I I I and W.C. Agosta, i b i d , 94, 7797 (1972).  -  185 -  41.  A.B. Smith, I I I and W.C. A g o s t a , I b i d , _95, 1961 (1973).  42.  A.B. Smith, I I I and W.C. A g o s t a , i b i d , 96, 3289 (1974).  43.  F o r another r e l a t e d  example, see A. M a r c h e s i n i , U.M. Pagnoni and  A. P i n e t t i , T e t r a h e d r o n L e t t . , 4299 44.  (1973).  H.E. Zimmerman and L. C r a f t , T e t r a h e d r o n L e t t . , 2131 (1964); D. Bryce-Smith and A. G i l b e r t ,  ibid,  2137 (1964).  45.  R.C. Cookson, D.A. Cox, and J . Hudec, J . Chem. Soc., 4499  46.  See r e f . 23 and r e f e r e n c e s c o n t a i n e d t h e r e i n .  47.  J.A. B a r l t r o p and B. Hesp, J . Chem. S o c , ( C ) , 1625 (1967).  48.  S.P. Pappas and N.A. P o r t n o y , Chem. Commun., 1126 (1970).  49.  E. Bergmann and F. Bergmann, J . Org. Chem., _3»  50.  I . F l e m i n g and D.II. W i l l i a m s , " S p e c t r o s c o p i c Methods  1  2  5  (1961).  (1938). in  O r g a n i c C h e m i s t r y " , McGraw-Hill Co. London, 1966. 51.  K. N a k a n i s h i , " I n f r a r e d A b s o r p t i o n S p e c t r o s c o p y - P r a c t i c a l " , Holden-Day, I n c . San F r a n c i s c o . 1962.  52.  C h e m i c a l s h i f t s o f AB systems where  IT. - T_ I < 6 J , were A B' AB c a l c u l a t e d by u s i n g t h e f o l l o w i n g f o r m u l a : 1 T  1  til where  Hz.  i s the s h i f t o f t h e  i  l i n e , r e l a t i v e t o TMS, i n  See r e f . 50.  53.  W.C. A g o s t a and S. W o l f f , J . Org. Chem., 40, 1665 (1975).  54.  See r e f . 23, p. 126.  - 186 -  55.  H. Labhart and G. Wagniere, Helv. Chim. A c t a . , 42, 2219 (1959); A. Moscowitz, K. Mislow, M.A.W. Glass and C. D j e r a s s i , J . Amer. Chem. S o c , 84, 1945 (1962);  D. Chadwick, D.C. F r o s t , and L.  W e i l e r , i b i d , 93, 4321, 4962 (1971). 56.  V a r i a n A s s o c , "High R e s o l u t i o n NMR Spectra Catalogue", 1963. Spectrum #638.  57.  D.M. Golden and S.W. Benson, Chem. Rev., 69, 125 (1969).  58.  L.F. F i e s e r and F.C. Chang, J . Amer. Chem. S o c , 64, 2043 (1942).  59.  L.F. F i e s e r , "Experiments i n Organic Chemistry", 2nd ed., D.C. Heath and Co. , Boston. 1941 p. 228.  60.  J . Attenburrow, A.F. B. Cameron, J.H. Chapman, R.M. Evans, B. A. Hems, A.B.A. Jansen and T. Walker, J . Chem. S o c , 1094 (1952).  61.  E.L. E l i e l , N.L. A l l i n g e r , S.J. Angyal and G.A. Morrison, "Conformational A n a l y s i s " , I n t e r s c i e n c e , New York. 1967. a) p. 42-44 b) p. 186.  62.  A.G. Brook, J . Chem. S o c , 5040 (1952).  63.  M.F. A n s e l l , B.W. Nash and D.A. Wilson, i b i d , 3012 (1963).  64.  D.G.I. F e l t o n and S.F.D. Orr, i b i d , 2170 (1955).  65.  The t - b u t y l protons i n t e r t - b u t y l acetate give r i s e to a sharp s i n g l e t at T8.55. 1963.  Varian A s s o c i a t e s , "High R e s o l u t i o n NMR Catalogue",  Spectrum #141.  66.  D. Walker and T.D.Waugh, J . Org. Chem., 30, 3240 (1965).  67.  M.F. A n s e l l , B.W. Nash and D.A. Wilson, J.Chem. S o c , 3028 (1963).  -  68.  187 -  See J.D. Roberts and M.C. C a s e r i o , C h e m i s t r y , " W.A.  Benjamin,  "Basic P r i n c i p l e s of Organic  I n c . , New York,  1965. p. 536 - 538,  f o r d i s c u s s i o n and the nmr o f 148 •<- 149. 69.  Duroquinone (151) was s y n t h e s i z e d from durene i n the manner of L . I . Smith, Org. Synth., C o l l . V o l . I I , 254 (1947), as f o l l o w s :  WO,  70.  J . Sauer, Angew. Chem. I n t . Ed. E n g l . , J5, 16 (1967).  71.  The i n t e r m e d i a c y o f a b i r a d i c a l has been demonstrated  i n the P a t e r n o - B u c h i  reaction  many times i n t h e l i t e r a t u r e . • F o r  example, T u r r o and W r i e d e h a v e shown t h a t i r r a d i a t i o n of 7 2  acetone i n the p r e s e n c e o f c i s o r t r a n s - l - m e t h o x y - l - b u t e n e ( i ) l e a d s to the f o r m a t i o n of oxetanes The  iii  - v i i n good  yield.  l o s s o f c o n f i g u r a t i o n o f t h e o l e f i n i c double bonds was  e x p l a i n e d by t h e f o r m a t i o n of i n t e r m e d i a t e iJL, which can s u f f e r bond r o t a t i o n p r i o r to oxetane  formation.  - 188 -  A  +  CH^O-CH = CH-C H 2  5  i , c i s or trans  hv  li, R = C H 2  5  or CH 0 3  R'= CH 0 or C H 3  CH X  R  —H  --ri -OCHj  OCH  3  -ri  2  5  H  --H  OCM. Ill  iv  v  vi  72.  N.J. Turro and P.A. Wriede, J . Amer. Chem. Soc. , 92, 320 (1970).  73.  For a d i s c u s s i o n of the non-concertedness of photochemical cyclobutane formation, see P. de Mayo, Acc. Chem. Res., 4_, 41 (1971) and references c i t e d t h e r e i n .  74.  For reviews see: D.R. A r n o l d , Advan. Photochem., j i , 301 (1968); a l s o L.L. M u l l e r and J . Hamer, " 1 , 2 - c y c l o a d d i t i o n Reactions", I n t e r s c i e n c e , New York 1967, p. 111.  - 189 75.  See N.E. Schore and N.J. Turro, J . Amer. Chem. S o c , 97, 2482 (1975) and references t h e r e i n .  76.  Th. F o r s t e r , Angew. Chem. I n t . Ed. Engl., 8, 333 (1969).  77.  J.E. Baldwin and S.M. Krueger, J . Amer. Chem. S o c , 91, 6444 (1969).  78.  F.D. Lewis, R.W. Johnson, and D.E. Johnson, J . Amer. Chem. S o c , 96, 6090 (1974).  79.  E.L. E l i e l , "Stereochemistry of Carbon Compounds", McGraw-Hill, New York 1962. a) pp. 151, 237 b) p. 248.  80.  D.C. Neckers, "Mechanistic Organic Photochemistry", Reinhold Corp.,.New York, 1967. p. 19.  81.  F.D. Lewis and T.A. H i l l i a r d , J . Amer. Chem. S o c , 94, 3852 (1972);  P.S. Wagner and J.M. McGrath, i b i d , 94, 3849 (1972).  82.  H.E. O'Neal and S.W. Benson, J . Phys. Chem., 71, 2903 (1967).  83.  F.D. Lewis, R.W. Johnson, and D.R. Kory, J . Amer. Chem. S o c , 95, 6470 (1973).  84.  Y.-M. Ngan, M.Sc Thesis, U n i v e r s i t y of B.C. 1975.  85.  A. Padwa and W. Eisenberg, J . Amer. Chem. S o c , 94, 5859 (1972) and references t h e r e i n .  86.  P.J. Wagner, i b i d , 89, 5898 (1967).  87.  E.C. Alexander and J.A. U l i a n a , i b i d , 96, 5644 (1974).  88.  P.J. Wagner, A.E. Kernppainen and H.N. Schott, i b i d , 9_5, 5604 (1973).  - 190 -  89.  W.C. Agosta and W.E. Schreiber, i b i d , 93, 3947 (1971).  90.  C C . Badcock, M.J. Perona, G.O. P r i t c h a r d and B. Pickborn, J. Amer. Chem. S o c , 91, 343 (1969);  J.C. Dalton and N.J  Turro, Ann. Rev. Phys. Chem., 21, 499 (1970); and J.D. Coyle, Chem. Commun., 1081 (1969);  J.A. B a r l t r o p P.J. Wagner and R.W.  Spoerke, J . Amer. Chem. S o c , 91, 4437 (1969). 91.  W.C. Agosta and S. W o l f f , i b i d , 97, 466 (1975).  92.  F.R. Jensen, L.H. Gale, and J.E. Rogers, i b i d , 90, 5793 (1968) and references c i t e d t h e r e i n ; 25, 623 (1971);  A. Rassat, Pure Appl. Chem.,  L. Kaplan i n "Free R a d i c a l s " , J.K. Kochi,  ed., Wiley, New York, 1973. Ch. 18. 93.  F.R. Jensen and C H . Bushweller, J . Amer. Chem. S o c , 91, 3223 (1969);  94.  F.R. Jensen and R.A. Neese, i b i d , 93, 6329 (1971)  J . Altman, H. G i l b o a , D. Ginzburg and A. Loewenstein, Tetrahedron L e t t . , 1329 (1967).  95.  J.T. Gerig and J.D. Roberts, J . Amer. Chem. S o c , 88, 2791 (1966).  96.  I t i s known that cyclohexene i s conformationally more mobile 97  than cyclohexane (E f o r conformational i s o m e r i z a t i o n f o r cyclohexene, cl  5.93 k c a l mole *;  f o r cyclohexane, 10.3 k c a l mole * ) . S i m i l a r l y ,  the energy b a r r i e r to conformational i s o m e r i z a t i o n i n cyclohex,anone (approx. 6 k c a l mole *) i s somewhat l o w e r cyclohexane.  6 l b  than that f o r  By analogy then, the presence of 6 sp centres  (two double bonds plus 2 carbonyl groups) i n the tetrahydronaphthoquinone r i n g system may be expected to reduce the energy b a r r i e r to conformational i s o m e r i z a t i o n to the extent that i n adducts  - 191 -  where hydrogens  are located  a t the b r i d g e h e a d p o s i t i o n s ,  c o n f o r m a t i o n a l r o t a t i o n about  the C, -C_ bond i s an e n e r g e t i c a l l y 4a 8a  possible process. 97.  F.R.  J e n s e n and C H .  B u s h w e l l e r , J . Amer. Chem. S o c ,  87,  3286 (1965). 98.  J . P. Louwerens, M.Sc.  99.  R.A.  100.  Cormier and W.C  Thesis,  U.B.C,  1975.  A g o s t a , J . Amer. Chem. Soc., 96, 618  The d e a c t i v a t i o n mechanism to ground  s t a t e adduct i s l i k e l y  hydrogen atom back t r a n s f e r from oxygen t o c a r b o n atom Cg,  (1974). a as  shown below.  T h i s mechanism has been shown to c o n t r i b u t e observed i n the N o r r i s h  II reaction.  to the  inefficiency  Such a p r o c e s s i n the  case of the D i e l s - A l d e r adducts s h o u l d be f a c i l i t a t e d when conformational mobility  i n the b i r a d i c a l  by the p r e s e n c e o f b r i d g e h e a d 101.  K.  intermediate i s r e s t r i c t e d  substituents.  Biemann, "Mass Spectrometry", M c G r a w - H i l l Book Co., New  1962.  Ch.  5.  York.  -  192 -  APPENDIX A  C a l c u l a t i o n o f Deuterium i n c o r p o r a t i o n Required  1 0 1  i n ene-dione 117.  a r e good mass s p e c t r a o f d e u t e r a t e d  compounds.  and  non-deuterated  >  Peak h e i g h t s i n non-deuterated mass //  height  266  (P)  65 mm  267 (P + 1)  13 mm  P + 1 = 20% P  Peak h e i g h t s  compound (measured i n mm).  (correction factor)  i n deuterated  compound.  mass #  height  266  28 mm  (P')  267 (P + 1 ) ' Subtract  250 mm  t h e c o r r e c t i o n f a c t o r from (P + 1 ) ' . 20% P' = 5.6  (P + 1 ) " = (P + 1 ) ' - 20% P' = 244.4 % D i n c o r p o r a t e d = 244.4 28 + 244.4  x 100 = 89.7%  

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