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Intramolecular photochemical cycloaddition of nonconjugated dienes Boire, Brian Anthony 1971

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INTRAMOLECULAR PHOTOCHEMICAL CYCLOADDITION OF NONCONJUGATED DIENES  BY  BRIAN ANTHONY BOIRE B.Sc.  (Hons.) Loyola of Montreal,  1967  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n the Department of CHEMISTRY  We accept t h i s thesis as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA November,  1971  In p r e s e n t i n g t h i s t h e s i s  i n p a r t i a l f u l f i l m e n t of the requirements  an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, the L i b r a r y s h a l l make i t  f r e e l y a v a i l a b l e f o r reference  I f u r t h e r agree t h a t p e r m i s s i o n f o r extensive  for  I agree t h a t and s t u d y .  copying o f t h i s  thesis  f o r s c h o l a r l y purposes may be granted by the Head of my Department or by h i s r e p r e s e n t a t i v e s . of t h i s t h e s i s  It  i s understood t h a t c o p y i n g or p u b l i c a t i o n  f o r f i n a n c i a l g a i n s h a l l not be allowed without my  written permission.  Department of The U n i v e r s i t y o f B r i t i s h Columbia Vancouver 8, Canada  Date  A/OU  3Q  .  /f7J  - ii -  ABSTRACT  The photolysis of isogermacrone (68)  has been investigated.  " s t r a i g h t " cycloaddition occurs to form syn (70)  and a n t i (71)  Exclusive 1,7-  2 6 dimethyl-4-isopropylidene-tricyclo[5.3.0.0  ' ]decane-3-one.  The structures  of the photoproducts have been confirmed by an independent synthesis. A mechanism, for the photolysis of _68, involving an intermediate  1,4-  d i r a d i c a l i s postulated i n order to account for the stereochemistry of the products. The d i r e c t and t r i p l e t - s e n s i t i z e d photochemistry of the three geometric isomers of d i e t h y l deca-2,8-diene-l,10-dioate been studied.  (79 - 81)  has  The t r i p l e t reaction i s one of rapid c i s , t r a n s isomerization  accompanied by slower 2 + 2  i n t e r n a l c y c l i z a t i o n i n a " s t r a i g h t " manner  to give four of the s i x possible stereoisomeric d i e t h y l octane-7,8-dicarboxylates  (82 - 85).  bicyclo[4.2.0]-  The stereochemistry of these products  as well as the t r i p l e t nature of the reaction are i n d i c a t i v e of a two step mechanism involving 1 , 4 - d i r a d i c a l intermediates.  Possible explanations  for the d i r e c t i o n of i n i t i a l bond formation i n these reactions are also discussed.  The d i r e c t  (singlet)  reaction of the  deca-2,8-diene-l,10-  dioates i s one of trans to c i s isomerization followed by a,3  to B,y  double bond migration from the Cis isomer; the sole deconjugated product is diethyl trans,trans-deca-3,7-diene-l,10-dioate. for t h i s s t e r e o s e l e c t i v i t y  A possible explanation  i s advanced.  Reasons for an i n v e s t i g a t i o n of the photolysis of cyclonona-2,6dienone (128)  and a scheme for i t s synthesis are presented.  - iii -  TABLE OF CONTENTS Page INTRODUCTION  1  A) Background  1  B) Cycloaddition Reactions  9  (1)  Intermolecular Photochemical Cycloaddition  9  (2)  Intramolecular Photochemical Cycloaddition  12  a) A c y c l i c  l  b) C y c l i c  2 8  C) Photodeconjugation  RESULTS AND DISCUSSION A) Isogermacrone  2  39  43 43  (1) Objectives and Choice of Starting M a t e r i a l  43  (2) Photolysis of Isogermacrone  44  (3)  45  Structure Proof of Photoproducts p_ and E  (4) Mechanistic Implications  49  (5) Conclusion  52  B) A c y c l i c Diene-diesters (1)  (2)  53  Introduction  53  a) Background and Objectives  53  b) Source of Starting M a t e r i a l  54  I r r a d i a t i o n i n the Presence of T r i p l e t Energy Sensitizers  55  a) Photolysis of 7_9, 80, and 81  55  - iv -  Page b) Characterization of Photoproducts 82,  83,  84,  and 85  57  c) Thermodynamic S t a b i l i t i e s of Photoproducts 82 - 85  59  (3) Discussion of Sensitized Photolyses of 7_9, 80_, and 81  62  a) Possible Mechanisms  62  b) I n i t i a l Bond Formation  71  (4) Direct Photolysis of Compounds 7 9 ,  80, and 115  a) Photolysis of 7_9_  83 83  b) Characterization of Photoproducts _79_ - J31_ and 115 - 117  84  c) The Photolysis of 80 and 115  85  d) Quenching Studies  86  (5) Discussion of the Direct I r r a d i a t i o n of Compounds •79, 80 and 115  86  Conclusion  88  C) Cyclonona-2,6-dienone  89  (6)  EXPERIMENTAL  92  A) General Procedures  92  B) Isogermacrone  93  C) A c y c l i c Diene-diesters  99  D) Cyclonona-2,6-dienone  BIBLIOGRAPHY  112  116  - v -  ACKNOWLEDGEMENTS  I would l i k e to express my gratitude for having the pleasure and opportunity to work under the supervision of D r . J . R. Scheffer.  His  effervescent  i n his  a t t i t u d e towards chemistry and h i s personal interest  students has made t h i s period of l e a r n i n g , i n my l i f e , both p r o f i t a b l e and enjoyable. The fresh outlook and relaxed atmosphere i n lab 346 w i l l always leave me indebted to those who made i t that way: Mel Lungle, Rocky Wostradowski, Dennis Ouchi, Ruedi Gayler, Barry Jennings, and Kuldip Bhandari. I am also very fortunate to be associated with such a great number of i n t e l l i g e n t and f r i e n d l y men as are found i n the Physical-Organic section of t h i s department.  Never once was I refused assistance from  anyone I approached. I am deeply indebted to the National Research Council of Canada for f i n a n c i a l support during the l a s t four years. F i n a l l y , I wish to express my sincere gratitude to my wife Pat for her u n t i r i n g patience and her excellent work on the diagrams i n t h i s manuscript.  - vi -  DEDICATION  To my  wife  Pat  and  To my Rose E.  parents  (Stacey)  Boire  and Anthony A.  Boire  INTRODUCTION  A) Background The need to investigate the photochemistry of organic molecules i n solution i s both synthetic and mechanistic i n nature.  In the past ten  years, photochemical preparative syntheses of unusual carbocyclic and heterocyclic r i n g systems have become a respectable and often used method. U s u a l l y , these systems are extremely d i f f i c u l t to obtain by conventional modes of synthesis. skeleton  2  (Eq 2),  The syntheses of cubane* (Eq 1),  and pinacols  3  the prostanoic acid  (Eq 3) are only a few of the many organic  systems which can make use of simple photochemical procedures.  Eq 1  Eq 2  - 2-  R.  \  / R  R R CHOH i-f  C=0  ^  R.  hV  1  OH | C  I  OH | C  I  R2  2  R,  Eq 3  1  ^2  In order to use organic photochemical reactions more f u l l y , an understanding of t h e i r mechanisms i s important.  The f i r s t step i n any  photochemical reaction i s the absorption of a quantum of l i g h t (E = hv) by a ground state ( S Q ) molecule (Eq 4).  S  The i n i t i a l l y formed e l e c t r o n i c  >  Q  Eq 4  >  ss.  S  Eq 5  ] L  •f-  species i s the v i b r a t i o n a l l y excited f i r s t s i n g l e t state ( S ^ ) which quickly relaxes (Eq 5) e s p e c i a l l y i n s o l u t i o n phase. s i n g l e t states ( S  2  >  S ^ , etc.)  E x c i t a t i o n to higher  i s possible with higher energy l i g h t , but  i t i s generally accepted that these higher states are too short —  (10  12  sec)  lived  A for any processes to occur except r a d i a t i o n l e s s decay to S ^ .  If only unimolecular processes are possible the excited s i n g l e t state has four possible modes of r e a c t i o n .  Fluorescence  (Eq 6) and i n t e r n a l  conversion (Eq 7) help to depopulate the s i n g l e t state i n approximately 10  sec.  These r a d i a t i v e and non-radiative deactivations  y  SQ +  hv  Fluorescence  are of  little  Eq 6  - 3 -  P  Internal Conversion  Eq 7  Rearrangement  Eq 8  Intersystem Crossing  Eq 9  i n t e r e s t to the organic chemist as no new product (P) i s formed.  The  excited or "hot" ground state that i s formed i n Eq 7 i s capable of rearrangement under low pressures, but usually deactivates quickly to 3 s t a r t i n g material i n s o l u t i o n .  In order f o r rearrangement (Eq 8) of the  state or f o r intersystem crossing (Eq 9) to occur, t h e i r rates must compete e f f e c t i v e l y with those of fluorescence and i n t e r n a l conversion 8 - 1 4 (10 sec ). There are three mechanisms suggested f o r the rearrangement of a molecule i n the  state to a new product molecule (P). The f i r s t  one involves a d i r e c t rearrangement which produces the excited s i n g l e t state of the product, followed by i n t e r n a l conversion to a "hot" ground state.  The second mechanism proposes a continuous rearrangement which  eventually produces a ground state product.  A t h i r d p o s s i b i l i t y , which  i s not l i k e l y to occur i n s o l u t i o n phase, i s rearrangement from the "hot" ground state of the reactant.  The l a s t process of intersystem crossing  (Eq 9) produces a v i b r a t i o n a l l y excited t r i p l e t state. relaxes to T^.  This quickly  The t r i p l e t state cannot be populated d i r e c t l y from the  ground state because i t i s a spin forbidden process.  Thus i t s existence  depends on the intersystem crossing e f f i c i e n c y and a process c a l l e d s e n s i t i z a t i o n which w i l l be described l a t e r .  In a manner analogous to the  - 4 -  singlet s t a t e , the t r i p l e t i s capable of r a d i a t i v e decay Eq 10),  (phosphorescence,  nonradiative decay (intersystem crossing, Eq 11) and rearrange-  ment (Eq 12)  to a new product (P).  long l i f e t i m e (10-10  T^  -4  >  The t r i p l e t state has a r e l a t i v e l y  sec) and thus has more time i n which to undergo  S  Q  +  hv  Phosphorescence  Eq 10  t T^  >  SQ  Intersystem Crossing  Eq 11  T  >  P  Rearrangement  Eq 12  reaction.  The mechanism by which the T^ state goes on to product i s a  l i t t l e more complicated than i n the s i n g l e t case.  The d i r e c t  rearrange-  ment and the "hot" ground state pathways are both p o s s i b l e , but the rearrangement  from the t r i p l e t state of the s t a r t i n g material to the  ground state of the product would involve a d i s c o n t i n u i t y due to the spin v i o l a t i o n process.  This i s usually the reason that concerted  reactions  are labeled as singlet state processes and t r i p l e t state reactions considered to proceed v i a an intermediate.  are  The primary processes i n  organic photochemical reactions discussed so f a r are best summarized with the aid of a Jablonski diagram"* presented i n F i g 1. Also indicated i n F i g 1 i s the fact that an e l e c t r o n i c a l l y species can deactivate  excited  i t s e l f by i n t e r a c t i n g i n a bimolecular f a s h i o n .  These bimolecular reactions  follow the Wigner rules'* of spin conservation.  Both excited s i n g l e t and t r i p l e t states are capable of t r a n s f e r r i n g  - 5 -  t h e i r energy to a ground state molecule.  In the former case, an excited  s i n g l e t acceptor and a ground state donor are formed (Eq 13).  In the  Fig 1  b and c  D(T,)  I A - acceptor; a -  ACS )  D - donor  excitation  b - v i b r a t i o n a l deactivation c - i n t e r n a l conversion d -  fluorescence  e - intersystem f -  crossing  phosphorescence  g - t r i p l e t energy transfer from D to A (A i s s e n s i t i z e d - D i s quenched)  D(S ) n  - 6 -  t r i p l e t case, a t r i p l e t acceptor and a s i n g l e t ground state donor are produced (Eq 1 4 ) .  In both of these cases the energy of the donor should  D  1  +  A  >  A  1  +  D  Eq 13  D  3  +  A  >  A  3  +  D  Eq 14  be equal to or greater than that of the acceptor i n order that e f f i c i e n t 4 exothermic energy transfer be accomplished. i s not w e l l understood.  The energy transfer mechanism  One mechanism involves the transfer  over r e l a t i v e l y long distances v i a dipolar interactions acceptor molecules.  of energy  between donor and  The other more common mechanism to s o l u t i o n photo-  chemists involves transfer  of energy by d i r e c t o r b i t a l overlap.  generally means c o l l i s i o n of donor and acceptor molecules.  This  Both of these  processes are predicted to have l i t t l e effect on the o v e r a l l geometry of 4 the molecules involved.  However, c e r t a i n distorted geometries are  often  proposed i n cases where endothermic energy transfer** appears to be occurring. These bimolecular energy transfer  reactions are referred to as  s e n s i t i z a t i o n or quenching depending on whether the donor or acceptor molecules are used as reference.  Both of these processes are  important to the organic photochemist. bimolecular energy t r a n s f e r , w i l l be described.  extremely  In order to narrow the topic of  only t r i p l e t state quenching and s e n s i t i z a t i o n  One of the most important aspects of organic  - 7 -  photochemistry i s to determine the m u l t i p l i c i t y of a given r e a c t i o n .  In  order to do t h i s i t becomes imperative that one i s able to exclusively populate either the s i n g l e t or t r i p l e t states of a molecule.  Triplet  s e n s i t i z a t i o n i s capable of putting a molecule into i t s t r i p l e t state w i t h out going through i t s s i n g l e t s t a t e .  Ketones, and i n p a r t i c u l a r  ketones, are extremely useful i n t h i s regard.  aromatic  They have almost unit 3  intersystem crossing e f f i c i e n c i e s and have high t r i p l e t energies  which  are capable of s e n s i t i z i n g a wide v a r i e t y of unsaturated compounds.  In  t h i s way, analysis of the d i r e c t i r r a d i a t i o n versus the sensitized reaction may produce meaningful r e s u l t s as i n the case of the i r r a d i a t i o n of 3,Y~ unsaturated ketones.  Direct^ i r r a d i a t i o n of 1_ r e s u l t s only i n product J2  Eq 15  Eq 16 1  (Eq 15),  3  whereas s e n s i t i z a t i o n  of 1 r e s u l t s only i n 3_ (Eq 16).  a good example showing the d i f f e r e n t r e a c t i v i t i e s t r i p l e t states.  This i s  of the s i n g l e t and  Usually, photochemical reactions are not as c l e a r - c u t  as  - 8 -  those mentioned above, and often require detailed k i n e t i c data i n order to d i s t i n g u i s h the r e a c t i v i t y of the two electronic states. for s e n s i t i z a t i o n are extremely important. be absorbed by the s e n s i t i z e r ,  The conditions  In general, a l l the l i g h t must  and the s e n s i t i z e r should not undergo any 3 5  chemical change under the reaction conditions. benzene (E = T  Common s e n s i t i z e r s  '  85 kcal/mole), acetone (E^= 78 kcal/mole), acetophenone  74 kcal/mole), benzophenone (E = T  69 kcal/mole), and naphthalene (E = T  are: (E^,= 61  kcal/mole). Quenching i s e s s e n t i a l l y the same as s e n s i t i z a t i o n except i n the opposite sense.  In other words, a compound i s added that absorbs no l i g h t  under the reaction conditions and i s capable of accepting t r i p l e t energy from an excited molecule.  In t h i s case the t r i p l e t energy of the quencher  must be lower than that of the reactant.  I d e a l l y , i f any t r i p l e t state  of the reactant i s formed during a p h o t o l y s i s , the quencher w i l l with i t immediately.  Thus i f any rearrangement  v i a the singlet state of the reactant.  interact  occurs i t i s proceeding  These two techniques are often  used i n d i s c r i m i n a t e l y as an i n d i c a t i o n of the m u l t i p l i c i t y of a r e a c t i o n . There are l i m i t a t i o n s to s e n s i t i z a t i o n and quenching techniques, and i f not combined with quantum y i e l d studies and k i n e t i c data,  should only be looked  upon as q u a l i t a t ive evidence.  They can however, be quite convincing as  i n the case of 3,y-unsaturated  ketones  (Eq 15 and  16).  In addition to knowing the m u l t i p l i c i t y of a r e a c t i o n , to know the mechanism involved.  i t i s important  While a considerable amount of  work has been done on the mechanisms of gas and s o l u t i o n phase i r r a d i a t i o n s , there are s t i l l many areas where  excellent  - 9 -  mechanisms are speculative and open to d i f f e r e n t interpretations and hence many areas that should be investigated.  One must not only be able  to d i s t i n g u i s h between concerted and non-concerted reactions but must be able to consider the p o s s i b i l i t i e s of exciplexes, transannular i n t e r a c t i o n s ,  charge-transfer  complexes,  and through-bond i n t e r a c t i o n s .  B) Cycloaddition Reactions  9 Cycloaddition reactions photochemistry.  form a large part of the f i e l d of organic  Even though a considerable amount of work has been done  i n t h i s area, the r e s u l t s are often stereochemically unpredictable and mechanistically obscure.  In general, t h i s class of reactions can be  divided into two main groupings: (1)  (1)  intermolecular and (2)  intramolecular.  Intermolecular Photochemical Cycloaddition In general, intermolecular photochemical cycloaddition occurs when  two o l e f i n i c moieties add to give a cyclobutane r i n g (Eq 17).  They have  hv  Eq 17  enjoyed the most synthetic use, but paradoxically, simple mechanisms are not a v a i l a b l e for these reactions.  Recently a review"*"^ has been published  on enone annelation which i s quite representative of t h i s c l a s s of reactions.  U s u a l l y , substituted enones are photolysed i n the presence of  excess o l e f i n under conditions where only the enone i s absorbing l i g h t .  - 10 -  The excited enone adds to the ground state o l e f i n and, v i a an undetermined pathway, forms a cyclobutane r i n g .  The dimerization of eye lop ent enone'''"''  12 the addition of cyclopentenone to cyclopentene (Eq 19), and the 13 addition of cyclohexenone to 1,1-dimethoxyethylene (Eq 20) are c l a s s i c (Eq 18),  Eq 18  hv  Eq 19  0 3  HC0^  ^QCH,  hv  OMe OMe  OMe OMe  examples of enone annelation.  It i s generally a c c e p t e d  10  that i t i s the  t r i p l e t state of the enone that i s undergoing c y c l o a d d i t i o n . s t a t e , as enones have low l y i n g mr* and  TTTT*  Eq 20  Which t r i p l e t  t r i p l e t states, i s the reactive  species i s uncertain, as evidence f o r either or both has been found.  The  immediate question now i s how the excited enone reacts with ground state o l e f i n to form product.  DeMayo has presented the following scheme''10  (Scheme 1) summarizing the postulates to date.  Route c involves a  - 11 -  Scheme 1  hv, $ i K  +  c  .3 K'  0  +  0  KO  competitive reactions  concerted formation of product.  Due to the complex nature of the products  formed (Eq 18 and 20) from enone annelation, t h i s mechanistic route appears to have very l i t t l e relevance.  However, i n simpler o l e f i n  14 dimerizations  there seems to be concrete evidence f o r t h i s pathway. 13  Corey found some r e g i o s p e c i f i c i t y  i n the photolysis of cyclohexenone i n  isobutylene, v i n y l ethers, a c r y l o n i t r i l e , and ketene a c e t a l .  He proposed  the formation of an excited state charge-transfer complex (exciplex) 3 between excited enone (K ) and ground state o l e f i n (0) (route a) based on the structure of the product  (Eq 21).  Cyclohexenone adds to methyl v i n y l ether  0  0 4  0  - 12 -  to form an exciplex 4_. This exciplex explains the o r i e n t a t i o n of the substituent i n the product.  There are, however, many reactions which would be  excluded on exciplex theory alone.  I t would be d i f f i c u l t to explain the equal  r a t i o of head to head and head to t a i l dimerizations of cyclopentenone (Eq 18). These r e s u l t s tend to favor an i n t e r p r e t a t i o n based on the formation 3 of the tetramethylene d i r a d i c a l ['K0-] .  However, rate studies do not  indicate the formation of such an intermediate, but require the i n i t i a l formation of an exciplex (Scheme 1, path a) to account f o r the observed kinetics. Other f a c t o r s , such as the e l e c t r o p h i l i c i t y of the excited enone, dipole-dipole i n t e r a c t i o n s , and the p o s s i b i l i t y of a trans enone i n t e r mediate have a l l been studied and found to play at least a p a r t i a l r o l e i n some reactions.  Only when a l l of these factors are assimilated w i l l a  unifying mechanism be possible. (2) Intramolecular  Photochemical CyclOaddition  a) A c y c l i c Unlike intermolecular cycloadditions there are two modes of addition open to a c y c l i c dienes.  They are able to add i n a " s t r a i g h t " (5) manner  hv  5  6  - 13 -  to form bicyclo[n.2.0] systems, or i n a "crossed" (6) manner to form b i c y c l o [ n . l . l ] systems. "' 1  addition i s equally l i k e l y .  A p r i o r i , i t would appear that either mode of However, i t can be shown from  experimental  evidence that the "crossed" versus " s t r a i g h t " nature of cycloaddition depends on the value of n. Srinivasan studied the mercury sensitized p h o t o l y s i s ^ of a series 1  of non-conjugated  dienes at t h e i r b o i l i n g points under atmospheric pressure.  He found that i n the case of 1,4 dienes (7_, _8, and 9) and 1,6 dienes (12) " s t r a i g h t " addition predominated and f o r 1,5 dienes (10 and 11) the "crossed" addition mode was most favored (Table 1). Table 1 Diene  Crossed/Straight  0.10  0.11  0.03  2.53  - 14 -  Table 1-cont. Dlene  Crossed/Straight  2.12 11  0.04  In order to explain h i s r e s u l t s by a common mechanism, Srinivasan postulated the i n i t i a l formation  of a f i v e membered r i n g followed  by  closure of the d i r a d i c a l species thus formed to the observed product (Eq 24).  This empirical "rule of f i v e " i s quite u s e f u l and few exceptions  22-  are  Eq  22  Eq  23  Eq  24  - 15 -  known.  I t does, however, disregard the r a d i c a l and thermodynamic  s t a b i l i t i e s of the intermediates and products r e s p e c t i v e l y .  A better  explanation i s needed to account f o r the observed s p e c i f i c i t y of i n i t i a l 1,5 bonding. 18 L i u and Hammond investigated  at approximately the same time the  photochemistry of substituted 3-methylene-l,5-hexadienes  (7a-d)•  Irradiat-  7a-d  ion of 7a_ or 7d_ i n the presence of a s e n s i t i z e r converts them into only 8a and 8d r e s p e c t i v e l y .  This i s another example of exclusive formation  of a "crossed" product (Eq 25).  In order to investigate the reaction  Eq 25  further they studied the photolysis of 7b and 7c. The same r a t i o (5.8 : 1.0) of products was formed i r r e s p e c t i v e of whether pure 7b_ or _7c was used as s t a r t i n g material (Eq 26).  Samples of 7b and _7c taken at incomplete  conversions showed that they had not l o s t their geometric purity. appears that a common intermediate i s i r r e v e r s i b l y formed.  Thus i t  This intermediate  - 16 -  must account f o r the r a t i o of products 9_ and 10_.  products.  They suggest that a f i v e  The authors give a v a r i e t y of reasons why the intermediate  d i r a d i c a l should be long l i v e d .  F i r s t l y , the Wigner hypothesis^ indicates  - 17 -  that the d i r a d l c a l should have t r i p l e t character as a r e s u l t of s e n s i t i z a t i o n and  secondly, there should be s t r a i n involved i n the formation of the  cyclobutane r i n g .  In order to explain the unusual s t e r e o s p e c i f i c i t y i n the  formation of a five-membered r i n g , L i u and Hammond suggest that i t i s probably due to k i n e t i c control of the f i r s t step.  They rejected  radical 19  s t a b i l i t y , as there i s ample evidence that r a d i c a l s t a b i l i t y with s u b s t i t u t i o n .  Furthermore, they rejected  increases  thermodynamic s t a b i l i t y 20  considerations as thermal e q u i l i b r a t i o n studies methylcyclopentane.  favor cyclohexane over  They state that "the preference f o r formation of f i v e -  membered rings may merely r e f l e c t the fact that the carbon atoms that become bonded are, on the average, closer together than those that would have to interact to form a six-membered r i n g " .  As added proof f o r t h i s  k i n e t i c control they point out that 5-hexenyl free r a d i c a l s 21 form cyclopentylmethyl r a d i c a l s  (Eq 27) even though r a d i c a l and thermodynamic  s t a b i l i t y both favor the cyclohexyl free r a d i c a l . i s highly substituted  preferentially  Only when the r a d i c a l  (R, = COOR, R = CN) does cyclohexyl r a d i c a l formation  Eq 27  predominate.  22  quite general  Even though t h i s behaviour of 5-hexenyl free r a d i c a l s i s  21-23  no s a t i s f a c t o r y explanation has yet been given.  L i u and Hammond's intermediate (11) has drawn the interest of K. Fukui,  24  - 18 -  He calculated the energies of the e l e c t r o n i c states of two model i n t e r mediates (11a and l i b ) based on structure 11_.  The f i r s t model (11a) has  carbons C. , C„, C„, C. , C,., and C,. a l l i n one plane while the second  •11a  model ( l i b ) has the C^,  Hb  axis perpendicular to a common plane shared  by carbons C_ , C , C„, C_, and C,. 1 2. j J o 0  Model l i b was  shown by extended Huckel  molecular o r b i t a l c a l c u l a t i o n s to be of lower energy than model 11a i n both the ground and excited state.  Fukui stated that 11a was most l i k e l y  the i n i t i a l species formed followed by the "true" intermediate l i b .  Fukui,  however, does not indicate the reason f o r the preference of 1,5 bonding i n t h i s system.  His major concern i s with the fate of the intermediate  once i t i s formed and not why  i t i s formed.  The t r i p l e t nature of these intramolecular cycloadditions has so f a r been taken f o r granted as a r e s u l t of the use of t r i p l e t  sensitizers.  In order to confirm the idea that the t r i p l e t state i s responsible f o r t h i s phenomenom, the d i r e c t  25  of myrcene (12) has been done.  (Eq 28) and sensitized  26  (Eq 29)  irradiation  The small amount of "crossed" product  formed under d i r e c t photolysis conditions probably r e s u l t s from a limited amount of intersystem crossing of the myrcene s i n g l e t .  - 19 -  Eq 28  Another diene system which has been investigated  i s 8-farnesene (13).  27 It was photolysed by White and Gupta.  under d i r e c t (Eq 30) and sensitized  (Eq 31)  As i n the case of myrcene the d i r e c t and  conditions  sensitized  i r r a d i a t i o n of 8-farnesene y i e l d s d i f f e r e n t products i n d i c a t i n g that  - 20 -  the "crossed" cycloadditions are p r i m a r i l y o r i g i n a t i n g from the t r i p l e t state of B-farnesene and that the low y i e l d of "crossed" products from the d i r e c t i r r a d i a t i o n i s a good i n d i c a t i o n of the intersystem  crossing  e f f i c i e n c y of the B-farnesene s i n g l e t state.  I t i s worthwhile to note  that " s t r a i g h t " additon occurs to some extent  i n B-farnesene under d i r e c t  i r r a d i a t i o n conditions. White and Gupta do not f e e l that k i n e t i c c o n t r o l of the f i r s t step bas on s t e r i c reasons i s s u f f i c i e n t to explain the preference  for 1,5 bonding.  They reason that since the reaction i s e s s e n t i a l l y quantitative, the k i n e t i c argument would "necessitate a highly oriented ground state of the substrate".  In order to explain the observed s p e c i f i c i t y they have  postulated an "oriented complex (16) of excited diene and ground state o l e f i n " i n much the same manner as Corey's explanation for the observed 13 s p e c i f i c i t y i n cyclohexenone annelation.  The excited diene moiety can  13 Eq 32  14 be considered  +  to have molecular o r b i t a l s s i m i l a r to butadiene.  15 Thus i t  w i l l have two electrons i n the lowest bonding o r b i t a l ty^j one i n the second bonding o r b i t a l ty^, and one i n the lowest antibonding  l e v e l ty^.  The c o r r e l a t i o n diagram (Fig 2) has the electron i nty^of the diene i n t e r acting with the bonding o r b i t a l ty- of the o l e f i n moiety and the electron  - 21 -  113.1 Diene  in  Complex  Olefin  of the diene i n t e r a c t i n g with the antibonding l e v e l ty^ of the o l e f i n .  Although not s p e c i f i c a l l y stated i n the above d e s c r i p t i o n of the complex, i t s geometry i s suggested to be of a one to one fashion as indicated i n structure 16.  A l l other combinations lead to rings with greater than s i x  carbon atoms and are thus less stable on thermodynamic grounds.  Then  White and Gupta further suggest that "subsequent bond formation from the complex may be determined by r a d i c a l s t a b i l i t i e s , at least where such bond formation proceeds stepwise or unsymmetrically so that the collapse" of the complex leads to 17.  Such an argument r a t i o n a l i z e s cycloaddition  and indicates a preference f o r "crossed" over " s t r a i g h t " cycloaddition at least i n the case of $-farnesene  itself.  Appropriate substituents are often used i n order to give a nonconjugated diene an u l t r a v i o l e t absorption i n a region e a s i l y accessible  - 22 -  to conventional l i g h t sources.  We have already seen the use of the  butadiene moiety and now i t w i l l be valuable to describe the use of the carbonyl as an a c t i v a t i n g group. One of the e a r l i e s t intramolecular photochemical cycloadditions was done by Ciamician and S i l b e r i n 1957.  28  i n 1908 followed by Buchi and Goldman  29  In t h i s experiment carvone (18) was subjected to C a l i f o r n i a  sunlight i n a Pyrex vessel for 6.5 months.  Carvone-camphor (19) was the  Eq 33  only product i s o l a t e d besides polymer.  Another more recent example  the photolysis of 1,5-hexadiene-3-one (20) by Scerbo (Eq 34). product 21 i s the only product observed.  is  "Crossed"  Both of these 1,5 dienes (18  Eq 34  and 20) exhibit their preference for "crossed" addition.  While quenching  and s e n s i t i z a t i o n work has not been done on these systems i t i s generally accepted that they are proceeding v i a an excited t r i p l e t  state.  - 23 -  Brown  '  i n h i s attempt to synthesize either the copaene or  bourbonene skeleton, photolysed the following 1,6 dienes (Eq 35). He  Eq 35  22a, R = OEt b, R = OH c,  R = CH  3  obtained i d e n t i c a l r e s u l t s under both d i r e c t and s e n s i t i z e d i r r a d i a t i o n s . Again the empirical "rule of f i v e " seems to hold as " s t r a i g h t " cycloadded products are formed.  Brown suggests that i t i s probably the t r i p l e t state  that i s reacting and that the t r i p l e t of one o l e f i n (24) i s attacking the  22a  ground state of the other to form a five-membered r i n g (25).  Besides  - 24 -  obeying the "rule of f i v e " Brown f e e l s that increased conjugation i n d i r a d i c a l 2_5_ increases i t s s t a b i l i t y . A notable  exception to the "rule of f i v e " was observed by Meinwald  i n h i s photolysis of 1,8-divinylnaphthalene (27).  (26) and  33  1,8-distyrylnaphthalene  Photolysis of a 0.002 M s o l u t i o n of 26 i n cyclohexane gave an 80 -  90% y i e l d of 28 and 29_ i n a r a t i o of 10 : 1 r e s p e c t i v e l y (Eq 36) .  Eq 36  26  28  S i m i l a r l y , photolysis of a 0.001  29  M solution of 2_7 i n ether yielded 40%  and 38% of "crossed" products 3_0_ and 31_ and 5% of " s t r a i g h t " cycloaddition product 32 (Eq 37).  These r e s u l t s are quite s u r p r i s i n g as "crossed"  Eq  27  30  31  37  32  cycloaddtion has only been observed as a major pathway i n 1,5  dienes.  Meinwald explains t h i s unusual s p e c i f i c i t y on the s t a b i l i t i e s of the ground state conformations  of _2j6_ and 27 (33 and 34)  Conformation  i s the most favorable i n the ground state and i t i s from t h i s  33  conformation  - 25 -  33 CR = Ph or H)  34 (R = Ph or H)  that "crossed" cycloaddition occurs.  " S t r a i g h t " cycloaddition products  a r i s e from the less preferred conformer  34. 34  In 1963 Cookson et a l . studied the photolysis of c i t r a l (a 1 : 1 mixture of c i s and trans isomers).  (Eq 38)  Although the major product  i s not a cycloadded one, the minor product, p h o t o c i t r a l B (35) i n an analogous manner to those previously mentioned.  i s formed  Both products can  Eq 38  be r a t i o n a l i z e d on the basis of i n i t i a l 1,5 bonding (36). (37)  Photocitral A  can then be formed by 1,4 hydrogen migration and p h o t o c i t r a l B by  bond formation.  Cookson f e l t that the reason for i n i t i a l bond formation  could be traced to a charge-transfer  complex of a pure l o c a l i z e d n,ir*  t r a n s i t i o n of the enone with the antibonding ir* o r b i t a l of the unconjugated double bond.  This charge-transfer  complex then overlaps both the oxygen  - 26 -  p - o r b i t a l and the enone ir* o r b i t a l .  Evidence for this l i e s i n the fact  that the e x t i n c t i o n c o e f f i c i e n t for c i t r a l i s 72 whereas that for g-methacrolein i s 25.  This i s almost a t h r e e - f o l d enhancement. 35  Later i n 1968 Cookson discussed i n h i s T i l d e n lecture Chemical Society the various r e a c t i v i t i e s  of the d i f f e r e n t  to the electronic  states of d i a l l y l and i t s d e r i v a t i v e s .  Compound 3_8 best describes  unique behaviour of the ground (Eq 39),  excited s i n g l e t  excited t r i p l e t  (Eq 41)  states.  (Eq 40),  the  and  The f i r s t two reactions are the f a m i l i a r  CN Ground  Eq 39  Excited  hv  38  Singlet  Eq 40  NC  Excited 38  Triplet  Cope rearrangement  :N  hv (sens.)  (3,3-sigmatropic  Eq 41  s h i f t ) and the 1,3-sigmatropic  shift  37 36 respectively.  Both are well documented.  '  The t r i p l e t state i s again  responsible for cycloaddition and proceeds i n the manner predicted by i n i t i a l 1,5 bonding. Cookson to construct  This s p e c i f i c electronic state behaviour prompted an energy l e v e l scheme (Fig 3) for d i a l l y l u t i l i z i n g  the four o r b i t a l s of the dienes and the two sigma o r b i t a l s of the central  - 27 -  3 , 4 sigma bond.  The levels at the l e f t are uncoupled as they would be i n  an isolated system.  In the middle, the 3 , 4 sigma bond i s i n a plane at  r i g h t angles to the plane of both double bonds.  The sigma bond then  e f f e c t i v e l y s p l i t s the l e v e l s of the IT and T T * states. the l e v e l s  and ty^* ^ 4  zero order approximation. Fig 3  a n d  Cookson f e l t that  ^ 5 ) could be reversed as t h i s was only a  - 28 This scheme does, however, predict that d i a l l y l w i l l have a long wavelength absorption, as this type of i n t e r a c t i o n brings the highest occupied molecular o r b i t a l and the lowest unoccupied molecular o r b i t a l closer together.  This p r e d i c t i o n , he claims, i s supported by the u l t r a v i o l e t  absorption of molecules possessing the necessary geometry.  On the r i g h t  (Fig 3) Cookson has drawn the molecular o r b i t a l s by increasing the number of nodes from zero to f i v e .  He points out that the highest occupied  molecular o r b i t a l T T explains the observed Cope rearrangement i n the s  thermolysis of d i a l l y l s . include 1,3  He did not, however, extend t h i s argument to  sigmatropic s h i f t s or cycloadditions.  A c y c l i c photochemical  cycloadditions of 1,4-  1,5- and 1,6  dienes  have been discussed and i t appears as i f they a l l have two properties i n common.  They obey the "rule of f i v e " and they are a l l t r i p l e t state  reactions.  With t h i s i n mind i t w i l l now be necessary to investigate  c y c l i c systems to see i f they behave i n an analogous manner. b) C y c l i c C y c l i c nonconjugated dienes are also capable of adding i n a "crossed" or " s t r a i g h t " manner (Eq 42).  Much less work has been done i n t h i s area  and as a r e s u l t , t h i s discussion w i l l be as complete as possible.  Since  the question of "crossed" versus " s t r a i g h t " cycloaddition i s of immediate  - 29 -  importance, t h i s discussion w i l l not be concerned with non-conjugated dienes which are constrained geometrically to add i n a s p e c i f i c manner. The largest group of such compounds can be i l l u s t r a t e d by Eq 43.  These  Eq 43  dienes react v i a the t r i p l e t state and usually produce caged r i n g systems by adding i n a " s t r a i g h t " manner. In general, c y c l i c 1,3 dienes close photochemically butenes rather than bicyclobutanes.  to give c y c l o -  Since the intersystem crossing  e f f i c i e n c y of dienes i s low, presumably these reactions are proceeding 39 v i a the excited s i n g l e t s t a t e .  1,3-Cycloheptadiene  closes i n a  Eq 44  d i s r o t a t o r y fashion to give bicyclo[3.2.0]-6-heptene  (Eq 44). The  behaviour of 1,3 dienes under i r r a d i a t i o n conditions may be best described as e l e c t r o c y c l i c reactions. 40 A c y c l i c 1,4 dienes usually undergo a di-ir-methane rearrangement  as  30  the major reaction pathway.  In contrast to t h i s , the r e s u l t s of Moon  41 and Ganz  concerning  quite unique.  the photolysis of 1,4-cyclooctadiene (39) are  Under d i r e c t i r r a d i a t i n g conditions they obtained a  quantitative y i e l d of syn tricyclooctane (40). The excited species reacting i s probably the s i n g l e t state.  A p r i o r i , i t could be said that  Eq 44  Eq 45  41 40 could a r i s e v i a i n i t i a l 1,5 bond formation but t h i s does not explain the geometry of the f i n a l product unless k i n e t i c closure of the d i r a d i c a l i s proposed.  It has been shown that j40_ i s converted into i t s a n t i  isomer 41_ (Eq 45) under thermolysis  conditions.  Thus the mechanism of 42  t h i s photolysis would best be described as an allowed  2 2 IT + i r c y c l o s s  addition. Of the 1,5 c y c l i c cycloadditions, none have been studied as extensively as cis,cis-1,5-cyclooctadiene  (42). In 1964 Srinivasan f i r s t  published  43 his  results  on the gas and s o l u t i o n phase photolysis of 1,5-cyclooctadiene  and i t s copper chloride complex (44). In the s o l u t i o n phase he was able to determine that the uncomplexed cyclooctadiene was the p r i n c i p l e absorber of the l i g h t .  This was based on the o p t i c a l density studies of  - 31 -  the components of the photochemical transformation of the complexed  Eq 46  Eq 47  43  (30%)  44 and uncomplexed forms of cyclooctadiene into 43.  Based on t h i s and  44 deuterium l a b e l i n g studies  Srinivasan postulated an  intramolecular  mechanism i n which 4_2_ absorbs the l i g h t , bonds i n a 1,5 manner, complexes with copper chloride, and then closes to product (Scheme 2).  This scheme  shows 42 (as opposed to the c i s , t r a n s and trans,trans isomers of cycloScheme 2  - 32 -  Scheme 2 - cbnt.  CuCl 43 octadiene)  as the immediate precursor of product 43. 45  In 1967 Cope and Whitesides synthesized the c i s , t r a n s  and trans,  46 trans isomers of 1,5-cyclooctadiene (45 and 46 r e s p e c t i v e l y ) . They investigated the photolysis of these isomers i n order to shed l i g h t on 47 the i r r a d i a t i o n s of 4_2_ and 44.  In 1969 they published a f u l l paper  that  pointed to the fact that the major amount of 43_ formed comes from the cis,trans  (45)  trans (46)  isomer and hints at the possible intermediacy of the trans,  isomer (See Table 2 and Scheme 3).  Unlike Srinivasan, they  photolysed 44_ i n pentane which r e s u l t s i n a heterogeneous mixture. Table 2 Substrate  I r r a d i a t i o n time (hrs)  42(%)  42  P  24  100  42  b  72  Maj or  44  P  44  On the  45(%)  46(%)  0  0  0  0  0  Trace  43(%  3  93  4  <1  3  p  24  62  13  -\>1  19  44P  48  28  17  'V'l  43  2  19  0  0  0  45  p  45  b  20  47  P  48  32  ^20  ^1  12  46  p  1  0  0  0  70  p - photolysis done i n pentane b - photolysis done i n benzene  Major  Minor  0  Trace  -  33  -  basis of the q u a l i t a t i v e observation that a s i g n i f i c a n t f r a c t i o n of the c i s , c i s isomer present  i n the pentane s o l u t i o n of the complex i s free  in s o l u t i o n , and on the basis of the s i m i l a r i t y between t h e i r system and that of Srinivasan's, they assumed that 42_ i s the primary l i g h t  absorbing  species i n the photolysis of a pentane suspension of 44_.  Thus based on  t h i s assumption and on the data i n Table 2 the following  mechanistic  pathways are suggested for the photolysis of 44_ (Scheme 3 ) .  This scheme  Scheme 3  44  +  42  JUL.  CuCl  CuCl  hv  hv,^  ^  +  46  presents  the c i s , t r a n s copper chloride complex  immediate precursors of 43.  They present  CuCl  47  47^  and 4j6 as the  several reasons why  they discard  - 34 -  the p o s s i b i l i t y of A2_ as the reactive species responsible for c y c l o a d d i t i o n . Neither d i r e c t nor sensitized photolysis of 42_ i n the absence of copper chloride y i e l d s detectable quantities of ^3_.  Furthermore,  the  appearance of 45_ and 46_ under the photolysis conditions (photolysis of and the fact that these i n turn can be photolysed to 43 (Table 2) suggest that these are intermediates.  strongly  Secondly, the r e l a t i v e y i e l d s of  45 and 43 show that the formation of 43_ depends on the concentration t h i s diene i n s o l u t i o n .  44)  of  This suggests that at least part of the c y c l o -  addition i s occurring from the c i s , t r a n s isomer (45).  The high steady  state concentration of 45_ during the l a t t e r stages of the photolysis combined with the r e l a t i v e l y high e f f i c i e n c y with which i t i s into tricyclooctane  (43)  i n the presence of copper chloride indicates that  a major portion comes from 45_. cleanly (70%)  F i n a l l y , photolysis of 4j[ gives 43  and photolysis of 47 y i e l d s the trans,trans isomer, and  despite i t s consistently low concentration, amount of  converted  could give r i s e to a s i g n i f i c a n t  43.  The authors f e e l that the i n t r i g u i n g p o s s i b i l i t y of the trans,trans isomer (46)  as a major contributor exists i f one can assume that the  extinction c o e f f i c i e n t of the complexes are i n the same r a t i o as that of the dienes.  In such a case one would have "at one extreme of  pretation the rates of formation of 43_ from 45_ and  inter-  precursors should  be approximately equal; at the other extreme the major f r a c t i o n of 43_ might be formed from the trans,trans diene". mechanism of a concerted  IT  If t h i s were so, a simple  2 2 + ir cycloaddition i s conceivable from the s s  - 35 -  Eq 48  twisted conformation (48)  of t r a n s , t r a n s - l , 5 - c y c l o o c t a d i e n e  (Eq 48).  A compound which could conceivably add i n a 1,5 manner to give either " s t r a i g h t " or "crossed" addition would be of considerable interest order to observe which manner of cycloaddition p r e v a i l s . of compounds would be the 1,5-cyclononadienes.  in  One such series  In 1965 Sutherland  p h o t o l y s e d ^ byssochlamic acid to give a single cycloadded product (Eq 49).  Eq 49  The product, however, was not completely i d e n t i f i e d and i t s  structure-  proof r e s t s s o l e l y on i t s thermal s t a b i l i t y . Not u n t i l 1968 did anyone investigate the photochemistry of nonconjugated 1,6-cyclodecadienes.  Based on the empirical rule of  bonding these can be predicted to add i n a " s t r a i g h t " manner. 1968 and early i n 1969  1,5Late i n  three separate papers dealt with the photochemistry  of c i s , c i s - c y c l o d e c a - 3 , 8 - d i e n e - l , 6 - d i o n e  t  ^,50,51  Scheffer and Lungle"^  - 36 -  established that the c i s , c i s isomer photolyses to the c i s , t r a n s isomer and that t h i s i s the immediate precursor of the ariti " s t r a i g h t " product  hv(Pyrex)  (Eq 50).  Eq 50  Benzene  A concerted r e a c t i o n of the c i s , t r a n s isomer to the observed product i s not possible and thus the authors suggest a d i r a d i c a l mechanism (Eq 51)  Eq 51  49  involving 1,5 bonding with subsequent bond r o t a t i o n and closure to form 49.  Exclusive formation of the a n t i isomer i s explained on the basis of  unfavorable s t e r i c interactions i n the formation of the syn isomer.  Here  again the p o s s i b i l i t y of a trans,trans intermediate i s conceivable as the 2 2 42 f i n a l product could then be obtained v i a a concerted ir + ir cycloaddition. s s Attempts to i s o l a t e t h i s intermediate under various conditions, however, 52 have not produced p o s i t i v e r e s u l t s .  The m u l t i p l i c i t y of the reaction  i s probably the t r i p l e t state as i t has been observed that the r e a c t i o n 52 proceeds i n the same manner under s e n s i t i z a t i o n conditions. 53 A less s p e c i f i c c y c l i z a t i o n was observed by Heathcock i n h i s  - 37 -  attempt to enter the copaene ring system v i a a cyclodecadienone (50). Photolysis of 50_ (double bond isomers of unknown geometry) i n ether led to both " s t r a i g h t " (51 and 52) and "crossed" (53) cycloadded products i n  Eq 52  - 53C22%) a 35 : 22 r a t i o r e s p e c t i v e l y .  These r e s u l t s are quite unique as a  s i g n i f i c a n t amount of product (53) a r i s e s v i a i n i t i a l 1,6 bonding. Germacrene D (54), a n a t u r a l l y occurring sesquiterpene was photolysed"''' by Yoshihara et a l .  This compound i s p o t e n t i a l l y a precursor of the  bourbonene or copaene systems depending on whether the cycloaddition proceeds  Minor amounts of  Eq 53  a-bourbonene and 3-copaene 54  55(major)  i n a " s t r a i g h t " or "crossed" manner r e s p e c t i v e l y .  I r r a d i a t i n g 54 under  d i r e c t conditions led mainly to (-)-8-bourbonene (55) and minor amounts  -  38 -  of a-bourbonene and 6-copaene (Eq 53).  P o s s i b l y , more copaene would  have been formed had the photolysis been done under t r i p l e t In order to explain the transannular  interactions  conditions.  56  (uv max = 259 nm,  e 4500) between the two double bonds, Yoshihara suggests that germacrene D prefers the conformation (56)  i n which the two double bonds i n the r i n g  56  are situated p a r a l l e l and face to face with each other.  The three  substituents are orientated i n the same d i r e c t i o n 3 to the r i n g .  It i s  from conformation 5_6 that Yoshihara explains h i s photolysis and thermolysis r e s u l t s of germacrene D. A c l o s e l y related system i s the photolysis" ^ of i s a b e l i n (Eq 54). 5  Here we have a 1,5 diene which adds i n a " s t r a i g h t " manner but c a r e f u l analysis of molecular models indicates that the r e s u l t i n g product derived  Eq 54  0 57  from "crossed" cycloaddition would be severely strained due to the presence  - 39 -  of the lactone r i n g . Sondheimer has reported the photocycloaddition of the largest c y c l i c 58 diene (58) system.  The addition proceeds r e a d i l y on exposure of 58 2 2 to sunlight and can be looked upon as a concerted photochemical TT + TT s s  hv cyclohexane  cycloaddition.  Eq 55 ^\  The structure proof of product 59, however, i s not  unequivocal and no m u l t i p l i c i t y studies were c a r r i e d out. As can be seen from t h i s survey, very l i t t l e has been accomplished i n understanding the mechanisms of c y c l i c photochemical cycloadditions of non-conjugated dienes.  There remains much to be done i n t h i s area.  C_) PhotodeConjugation a,3-Unsaturated carbonyl compounds having a y hydrogen atom are capable, under photolysis conditions, of the migration of the double bond 59 to the 8,Y p o s i t i o n . While t h i s phenomenon has been observed i n acids . . 60,61 , _ 62-65 . « . , ketones and esters, only the l a t t e r appears to have been fc  studied to any extent. 62 In 1968, Barltrop and W i l l s " " sought to find a mechanism which would explain deconjugation.  I r r a d i a t i o n of the trans compound J5_0 under d i r e c t  conditions led to a rapid interconversion of c i s and trans isomers (Eq 56).  - 40 -  This was followed by the formation of the 3,Y isomer (62).  Photolysis of  the c i s isomer was almost i d e n t i c a l except that no induction period for the formation of 62 was observed.  H  COOEt  \  /  CH  hv  /  hv  A A ^ " A A  CH„  H  H  J  COOEt  3  \  >  I r r a d i a t i o n under t r i p l e t conditions  .  ^  /  H  60  00Et  Eq 56  —  61  Cbenzophenone, acetophenone,  and acetone) led to c i s , t r a n s isomerization  but no photodeconjugation was observed.  Barltrop f e e l s that i t i s the  62 n,Tr* s i n g l e t that i s responsible for deconjugation probably the  n,Tr*  whereas i t  is  t r i p l e t state doing the c i s to trans isomerization.  He  proposes an intramolecular y hydrogen abstraction by the oxygen to form a dienol (63)  which ketonizes to form the observed product (Scheme 4).  Scheme 4 CH \  COOEt  3  /  A A  H  C  hV  H  S  H >  2  c  _  .c  0 E t  v.  '  A A  H  COOEt .  >  A A  H  H  v  .  HO  '  \  H  - 41 -  This mechanism i s supported by the fact that the double bond must be i n the c i s configuration i n order for deconjugation to occur.  The mechanism  i s further supported by the fact that when ethyl crotonate i s photolysed in methanol-OD the products contain at least 97% of one deuterium at carbon atom adjacent to the ester group.  There i s also a solvent  i n which the reaction proceeds f a s t e r i n a l c o h o l i c solvents. either be ah effect on the quantum e f f i c i e n c y of the hydrogen abstraction  the  effect  This may  intramolecular  leading to the dienol or the ease of ketonization  of the dienol to the 8,y  isomer. 63  At the same time Jorgenson photolysis of 64.  confirmed these r e s u l t s by studying the  Only c i s to trans isomerization was observed under  Scheme 5  sensitized conditions but under d i r e c t were also formed (Scheme 5) .  i r r a d i a t i o n conditions j>6 and 67  Jorgenson f e l t that j56_ (deconjugation) was  coming from the s i n g l e t state of the c i s isomer, whereas 67_ was coming from the singlet state of the trans isomer.  If 6\5 i s photolysed i n  methanol-OD both 6j6 and 67_ are formed possessing one deuterium at  the  - 42 -  a carbon.  This she f e e l s supports the dienol intermediate formed v i a  an intramolecular hydrogen transfer (Scheme 4). Further support f o r the dienol intermediate i n photodeconjugations comes from the work^ of Noyori et/al_. on the photolysis of an o t , 3 1  unsaturated ketone (Eq 57).  Dienols 6_5 and 66 were formed i n 80% y i e l d OH  CJ  \^C0CH3  67  i n a r a t i o of 5 : 1 r e s p e c t i v e l y .  Heating the dienol mixture at 100°  for 2 hr afforded deconjugated product (67) and s t a r t i n g material (64) i n an 83 : 17 r a t i o r e s p e c t i v e l y . Early i n 1968 Rando and Doering studied the photodeconjugation of a 59 series of substituted a,3-unsaturated esters and acids (Eq 58).  R  i  ^CH-CH=CH-C-0R(H) R  Rn  0  2  —  *  0  C=CH-CH -C-OR(H) R  They  Eq 58  2  observed, i n the case of the acids (R- = n-C-H „, n-C^H , and n - C H ; n  R  2  1c  10  0C  = H), that both c i s and trans 8,y-unsaturated products were formed.  A trans to c i s r a t i o of 2 : 1 was observed f o r these reactions.  - 43 -  RESULTS AND DISCUSSION  A)  Isogermacrone  (1) Objectives and Choice of Starting M a t e r i a l Before 1969 the photochemistry of nonconjugated medium-sized r i n g dienes was e s s e n t i a l l y an untouched area of research.  With the exception  42-47 of some extensive work done on 1,5-cyclooctadiene and 3,8-cyclodeca49-51 41 53 diene-l,6-dione only two other compounds ' were photolysed i n which the f i n a l products were characterized.  Thus a further i n v e s t i g a t i o n  i n t h i s area promised to be both i n t e r e s t i n g and u s e f u l . The choice of a s t a r t i n g material was based on three properties which i t must possess:  1) a nonconjugated medium r i n g c y c l i c diene,  2) an e a s i l y accessible u l t r a v i o l e t region, and 3) easy a v a i l a b i l i t y . Isogermacrone  (68) f u l f i l s a l l these requirements.  1,6-cyclodecadiene  It has a basic  skeleton, an e a s i l y accessible u l t r a v i o l e t region  (uv max 334 nm, log e 1 . 9 2 3 ) ^ and can be prepared i n one step from the 66 n a t u r a l l y occurring sesquiterpenone germacrone (69).  Generous samples  of germacrone were received from D r . M. Suchy, Czechoslovak Academy of  - 44 -  Science, and F r i t z s c h e Brothers, Inc., New York, N.Y.  Germacrone was  converted to isogermacrone under basic conditions i n reasonable y i e l d s . A s o l u t i o n of germacrone i n 0.5 N a l c o h o l i c potassium hydroxide was refluxed f o r four hours (Eq 59).  •  This gave a f t e r conventional workup  5 N K 0 H  ->  I  I  Eq59  Ethanol A, 4 hrs 69  68  procedures, followed by column chromatrography, pure c r y s t a l s of isogermacrone, mp 48° - 50° ( l i t . ^ mp 51° - 52°).  The geometry of  the C . C and c . C„ double bonds i n germacrone have been established 3' 4 7' 8 67 6  by nmr observations  to be trans with respect to the cyclodecane r i n g .  However, i n isogermacrone while the geometry of the C^,  double bond  i s probably trans only the trans configuration of the C.,, C 7  i s known with c e r t a i n t y . ^  0  double bond  8  Isogermacrone, prepared by the above method,  i s a s i n g l e isomer as indicated by various t i c and vpc experiments.  The  s p e c t r a l data (mass spectrum, i r , and nmr) are i n complete agreement with 66 those reported by Ohloff. (2) Photolysis of Isogermacrone 68 Photolysis of a 0.1% benzene solution of isogermacrone  under the  conditions indicated (Eq 60) led to the formation of seven new products A - G i n the following percentages:  A, 0.5%; B, 4.5%; C, 2.4%; D, 48.4%;  - 45 -  E, 29.5%; F, 5.2%;  and G, 9.4%.  Photoproducts D and E, the major  products (78%), were isolated and p u r i f i e d by preparative vpc.  Compounds  hv,N ,Pyrex  A (0.5%) + B (4.5%) +.  450 W Hanovia  C (2.4%) + p (48.4%) +  2  Eq 60  E (29.5%) + F (5.2%) + 68  G (9.4%)  A, IS, and C_ were found to be too v o l a t i l e to permit i s o l a t i o n .  Compounds  F_ and G_ were c o l l e c t e d i n s u f f i c i e n t amounts by preparative vpc to obtain crude s p e c t r a l data.  (3) Structure Proof of Photoproducts D_ and E of D_ and E indicated the absence of any  Spectral data ( i r and nmr)  v i n y l hydrogens and the presence of a ketone and an isopropylidene group. Mass spectra and  elemental  analyses confirmed t h e i r isomeric r e l a t i o n -  ship with s t a r t i n g material.  On the basis of t h i s preliminary evidence  i t was concluded that cycloaddition had taken place between the C^, and the C.,, C  Q  double bonds.  a v a i l a b l e to isogermacrone.  C^  There are two possible modes of cycloaddition "Straight" bonding, derived from i n i t i a l  bonding, produces two possible isomers 7_0 and 7_1.  1,5-  "Crossed" bonding,  derived from i n i t i a l 1,6 bonding gives only the symmetrical structure 72. The p o s s i b i l i t y of structure 7_2 was discounted on the basis of s p e c t r a l evidence (mass spectrum, i r , and nmr). large peaks at m/e  96 and at m/e  The mass spectra of p_ and E showed  122 corresponding to cleavage of the  - 46 -  cyclobutane r i n g i n structures 70_ and 7_1.  Furthermore, there i s no common  fragmentation pattern between the mass spectra of p_ and _E, and  70  71  ylangene and copaene;  that of  72  the l a t t e r two have the basic t r i c y c l o [ 5 . 3 . 0 . 0 ] -  decane skeleton as i n 72. The i n f r a r e d spectra of p_ and E_, which were very s i m i l a r , showed strong absorptions  at 5.88  u (carbonyl) and at 6.14  The peak heights of these absorptions  u (isopropylidene).  are approximately equal and can  attributed to a five-membered r i n g structure as present 70 and 7_1 (See F i g 4 ) . ^  be  i n structures  i n structure 77 the carbonyl absorption would  Fig_ 4  (a - Intensity of i n f r a r e d C=0  stretch/Intensity of i n f r a r e d C=C  stretch)  be expected on the basis of the data i n F i g 4 to be around four times more intense than the isopropylidene s t r e t c h .  Further confirmation of a  five-membered r i n g structure for photoproducts p_ and E,  comes from the  - 47 -  proximity of their carbonyl absorptions of 5.88  u to 5.87  p instead of  to 5.93 u which i s associated with a six-membered ring structure (Fig4 ). The nmr spectra of p_ and E_ are generally featureless with the exception of the  and C^  methyl s i n g l e t s .  2  In both p_ and E these are  nonequivalent which i s not compatible with the symmetrical "crossed" product 72_.  In the syn structure (70) the  and C^  methyl groups are  2  r e l a t i v e l y f a r from the e f f e c t s of the carbonyl as determined molecular model examination. the  However, i n structure 7_1 both the  and  methyl groups should be s i g n i f i c a n t l y s h i e l d e d ^ by the anisotropic  e f f e c t of the carbonyl. (CDC1 ) T 8.81 3  nmr  by  (s, 3, C - C H ) , and 8.92  (CDC1 ) T 9.10 3  On the basis of t h i s observation p_ [ p a r t i a l nmr 12  (s, 3,  3  C 1 2  ~  C H  3^'  a n d  (s, 3, C^-CH^]  9 , 1 7  assigned structures 70_ and 71_ r e s p e c t i v e l y .  3  '  C  n~  C H  and E [ p a r t i a l  3^  w  e  r  e  In both cases the downfield  methyl s i g n a l was assigned to the more remote C^  2  methyl group based on  a similar argument of carbonyl s h i e l d i n g . Unequivocal proof of structure was derived from an synthesis of 70_ and 71.  independant  Use was made of the w e l l known photochemical  addition of enones to alkenes (enone a n n e l a t i o n ) . ^ In t h i s case  Eq 61  74  - 48 -  cyclopentenone was photolysed i n an excess of 1,2-dimethylcyclopentene to give a 5 : 3 mixture of photoadducts 7_3_ and 7_4 r e s p e c t i v e l y (Eq 61) . The gross structures of 73 and 7_4 were v e r i f i e d by mass spectra, i r , and nmr.  The nmr also supplied the information needed i n assigning the  syn or a n t i configuration. T 8.55  The major product [ p a r t i a l nmr  (s, 3, C - C H ) , and 8.93 12  [ p a r t i a l nmr  3  (CDC1 ) T 8.99 3  (CDCl^)  (s, 3, C^-CH^)] and the minor product  (s, 3, C ^ - C H y , and 9.11  (s, 3,  were assigned the structures of _73_ and 74_ r e s p e c t i v e l y .  C^-CE^]  S i m i l a r l y , based  on the argument of the shielding influence of the carbonyl, the downfield s i n g l e t was assigned to the more remote C^  2  methyl group.  Two approaches were taken i n order to extablish the structures of photoproducts D_ and 15 as 70_ and 7_1_ r e s p e c t i v e l y .  The f i r s t of these  involved the sodium amide a l k y l a t i o n of 7_3 and 74_ with isopropyl bromide. The products of these were then compared to the hydrogenation products of D_ and E (Fig 5 ) .  While the s p e c t r a l data ( i r , nmr, and mass spectra)  Fig 5  D  NaNH,  H -Pt0 ethyl acetate 2  2  isopropyl bromide  73  75  E  Na  H -PtO ethyl acetate 2  ?  >  NH  2  isopropyl bromide 76  74  - 49  -  showed the products obtained from each method to be quite s i m i l a r , there were enough differences to warrant further evidence.  These s l i g h t  differences could a r i s e from the fact that the isopropyl group i s capable of e x i s t i n g i n either the endo or exo p o s i t i o n .  Undoubtably 7_5 and 76  synthesized by the above procedures are a mixture of these two stereoisomers. The second attempt involved the d i r e c t synthesis of 70 and 71. Adducts 7_3 and 74_ were condensed with acetone i n the presence of excess 72 sodium ethoxide.  Compounds 70 and 71 prepared i n t h i s manner from  Acetone NaOEt-EtOH  Acetone NaOEt-EtOH 71 and E 73 and 1J\_ r e s p e c t i v e l y were i d e n t i c a l ( i r , nmr, mass spectra, vpc retention times) to photoproducts p_ and 12 i s o l a t e d from the photolysis of isogermacrone.  (4) Mechanistic Implications The major products derived from the photolysis of isogermacrone can be formally explained as a r i s i n g from i n i t i a l 1,5 bonding of the  - 50 -  nonconjugated diene moiety.  "Crossed" addition which would involve  i n i t i a l 1,6 bonding does not occur as the crude s p e c t r a l properties of the minor products (F and G) indicate unsymmetrical type products incompatible with the symmetrical "crossed" compound 72. The p o s s i b i l i t y of photoproducts 70_ and _71 a r i s i n g v i a a concerted TT  2 2 + TT s s  cycloaddition offers no explanation f o r the formation of both  syn and a n t i tricyclodecanes.  As there i s no evidence of any geometric  isomers of ji8_ forming during the photolysis, a concerted pathway appears very u n l i k e l y .  The formation of both possible " s t r a i g h t " cycloadducts  could be interpreted as i n d i c a t i n g a two-step mechanism involving a d i r a d i c a l intermediate (77 or 78) which i s capable of closing i n two d i f f e r e n t Scheme 6  70 + 71  ways to y i e l d the observed products _70_ and 71^ (Scheme 6) .  Presumably,  based on known r a d i c a l s t a b i l i t i e s ,  d i r a d i c a l 78_ would be the most  l i k e l y intermediate e n e r g e t i c a l l y .  The preference for formation of 7_0_  - 51 -  could then be explained on the basis of less s t e r i c hindrance i n i t s formation.  Molecular models support the idea that the two methyl groups  i n a syn r e l a t i o n s h i p to the cyclopentenone ring involves more s t e r i c interactions than the methylene groups of the cyclopentane ring i n a similar syn r e l a t i o n s h i p .  It appears l i k e l y that both methyl groups are  needed to a f f e c t the product d i s t r i b u t i o n .  Heathcock and Badger f i n d a 53  10 : 1 r a t i o of a n t i to syn products i n the photolysis l,6-cyclodecadien-3-one (Eq 52).  of 6-methyl-  Further evidence f o r the influence of  the two methyl groups on product formation comes from the 5 : 3 r a t i o of syn to a n t i products formed i n the photoaddition of to cyclopentenone  1,2-dimethylcyclopentene  (Eq 61).  This exclusive " s t r a i g h t " cycloaddition for c y c l i c 1,6-dienes i s 50 51 54 55 i n accord with those reported. ' ' ' The major exception to t h i s i s worthy of note. Heathcock and Badger photolysed 6-methyl-l,6-cyclodecadien-3-one (Eq 52) which i s s t r u c t u r a l l y s i m i l a r to isogermacrone. ether  5 3  they obtained a mixture of 51 (32%), 52^ (3%), and 53 (22%).  In  In  54 hexane  solution they obtained a 51_ to 5_3_ r a t i o of 2 : 1.  However, under  the same photolysis conditions cyclodecadienone _50_ y i e l d s a _51_ : 5_3_ r a t i o of 9 : 1. product 53.  This r e s u l t strongly indicates a t r i p l e t precursor f o r "crossed" This seems to be i n accord with m u l t i p l i c i t y r e s u l t s obtained 26 27  for "crossed" product formation i n the photolysis of 1,5 dienes.  '  However i t cannot be concluded on the basis of t h i s data that the t r i p l e t excited state i s not responsible f o r " s t r a i g h t " cycloaddition products 51 and 5_2.  There i s ample evidence e s p e c i a l l y i n 1,6 and 1,7 dienes that  the t r i p l e t state i s the excited state responsible for " s t r a i g h t " cyclo-  - 52 -  addition.  '  Unfortunately the photolysis of isogermacrone cannot  shed any l i g h t on t h i s problem as the excited state species responsible for  (5)  exclusive " s t r a i g h t " addition i s at present unknown.  Conclusion It  i s evident that more work i n the area of the photochemistry  c y c l i c nonconjugated dienes i s necessary.  Many factors concerning the  nature of the cycloaddition are s t i l l i n doubt. give a reasonable y i e l d of "crossed" product?  Why  Why  does compound 50_  do a l l other c y c l i c  1,6 dienes give only " s t r a i g h t " a d d i t i o n products?^"*  Are the " s t r a i g h t "  and "crossed" products coming from the same excited species? only a few of the questions that s t i l l have to be answered. however, remain f a i r l y c e r t a i n :  These are Two  things  C y c l i c 1,6 dienes i n general prefer to  cycloadd by i n i t i a l 1,5 bonding and give products i n d i c a t i v e of a step mechanism.  of  two-  - 53 -  B) A c y c l i c Diene-diesters  (1) Introduction a) Background and Obj ectives A c y c l i c non-conjugated  dienes are capable of photochemically  cycloadding to form bicyclo[n.2.0] or bicyclofn.1.1] systems, where n i s the number of carbon atoms between the double b o n d s . T h e "rule of five"'''^ predicts " s t r a i g h t " bonding f o r systems with n = 1 and 3, and "crossed" bonding f o r systems with n = 2 (Eq 62).  Experimental r e s u l t s  9 i n general support these predictions quite w e l l .  Up u n t i l 1969, when the  Eq 62  "Straight"(n = 1, 3)  "Crossed"(n = 2)  present project was begun, no a c y c l i c diene system with n = 4 ( i . e . , a 1,7-diene) had been studied.  By i n v e s t i g a t i n g the photochemistry of  a c y c l i c dienes with n = 4 and greater, the "rule of f i v e " w i l l be inapplicable as i n i t i a l 1,5 bonding w i l l be impossible.  Other factors  such as the distance between the o l e f i n moieties, and the s t a b i l i t i e s of the rings formed may be more important as n i s increased.  In diene systems  with n = 5 or greater, however, molecular models indicate that there may be no d i s t i n c t i o n between a "crossed" or " s t r a i g h t " cycloaddition mechanism. If n i s s u f f i c i e n t l y large i t would be impossible to determine whether a  - 54 -  bicycle-[n. 1.1] (Eq 63).  system was formed v i a "crossed" or " s t r a i g h t " bonding  In these cases, the o l e f i n moieties would have to be looked  Eq 63  upon as i s o l a t e d double bonds.  With n = 4 there are too many non-bonding  interactions f o r a " s t r a i g h t " cycloaddition mechanism f o r the formation of a b i c y c l o [ n . l . l ] system.  Thus a 1,7 diene would make an i d e a l s t a r t i n g  material f o r the i n v e s t i g a t i o n of a c y c l i c photochemical cycloadditions where the "rule of f i v e " i s i n a p p l i c a b l e . i n v e s t i g a t i o n were the geometric  The compounds chosen f o r t h i s  isomers of diethyl-2,8-decadiene-l,10-  dioate (79, 80, and 81). COOEt OOEt  OOEt  OOEt 79  COOEt  COOEt  b) Source of Starting M a t e r i a l Diene-diester ]9_ has an e a s i l y accessible n,7r* u l t r a v i o l e t absorption 73 (uv max 241 (e 410) nm) region and can be e a s i l y prepared by known 74,75 l i t e r a t u r e procedures. Sebacic acid (1,10-decanedioic acid) was  - 55 -  converted into i t s d i a c i d chloride s l i g h t excess of t h i o n y l chloride.  (Scheme 7) by heating at 90  ina  The d i a c i d chloride was photobrominated  by the dropwise addition of bromine i n the presence of l i g h t .  The r e s u l t i n g  Scheme 7  COOH S0C1.  'C0C1  COOH  -C0C1 1) hv, Br 2' 2) Ethtnol  COOEt  DMF  -COOEt 79 74  mixture was e s t e r i f i e d with absolute alcohol  (Scheme 7 ) .  The dibromo-  d i e s t e r was then converted to 7_9 by r e f l u x i n g i n dimethyl formamide. Diene-diester 79, bp 104° at 0.02 mm ( l i t . characterized  by i t s spectral properties  7 5  75  bp 127° at 0.28 mm) was  which w i l l be discussed l a t e r .  A small amount of the cis,trans isomer J50 was also obtained by the above method but i t was found more p r a c t i c a l to synthesize t h i s isomer and isomer 81 by photochemical means. (2) I r r a d i a t i o n irt the Presence of T r i p l e t Energy Sensitizers a) Photolysis  ©f 79_, 80, and 81  Diethyl trans,trans-deca-2,8-diene-l,10-dioate (79) (5 mmol i n 400 ml  of acetone) was photolysed  under Corex optics using acetone (E^, = 78  kcal/mole) as a t r i p l e t energy s e n s i t i z e r and solvent (Scheme 8).  Under  these conditions greater than 98% of the l i g h t was absorbed by the acetone (See Experimental).  The course of the reaction was followed by  a n a l y t i c a l vpc. I n i t i a l l y , an equilibrium mixture of the geometric isomers Scheme 8  - 57 -  82_ (42%), 83 (15%), 84 (36%), and 85 (7%) remained.  The equilibrium r a t i o  of 7_9 : 80 : 8>1 remained constant at 3.8  throughout the  : 3.5  : 1.0  photolysis (from 6% to 94% conversion to the f i n a l product A similar equilibrium mixture of 7_9 - 81_ was (E^, = 74 kcal/mole) as s e n s i t i z e r  mixture).  formed using acetophenone  (benzene solvent, Pyrex f i l t e r ) .  Continued i r r a d i a t i o n s i m i l a r l y gave 82^ (45%), 83 (16%), 84_ (31%), and 85 (8%).  Benzophenone was also found to s e n s i t i z e  c y c l i z a t i o n but  naphthalene f a i l e d to produce any change i n 7_9 during i r r a d i a t i o n . Diene-diesters 80_ and 81_ were isolated by preparative vpc.  Their  characterization w i l l be described i n the section concerning the d i r e c t i r r a d i a t i o n of the diene-diesters 7_9 and 80. photolysed  Diene-diester 80_ was  i n the presence of acetone and gave an i d e n t i c a l equilibrium  mixture of 7_9_ - j?l_ as i n the sensitized  i r r a d i a t i o n of 19_ (Scheme 8).  Continued i r r a d i a t i o n gave photoproducts 8_2_ - 85_ i n the following y i e l d s : 82 (44%), 83 (18%), 84 (31%), and 85 (7%). Diene-diester 8JL s i m i l a r l y , upon acetone s e n s i t i z a t i o n , gave a mixture of 79 - 81_ (Scheme 8). and continued  However, an equilibrium mixture was never obtained  i r r a d i a t i o n gave photoproducts S2_ - 85_ i n s l i g h t l y  d i f f e r e n t percentages:  82 (26%), 83 (17%), 84 (49%), and 85 (8%).  b) Characterization of Photoproducts 82, 83, 84, and  85  The gross structures of 82_ - 8_5 were indicated by mass spectral parent peaks at m/e  254.  Nmr  spectra indicated the absence of v i n y l  hydrogens and the i r spectra showed the presence of a saturated ester carbonyl.  In order to determine the s p e c i f i c structures of the photo-  products 82, 83, and 84 their independent systhesis was  undertaken.  By  - 58 -  the method of de Mayo,  77  d i e t h y l maleate was photolysed i n the presence of  an excess of cyclohexene (Eq 64).  The photoadducts corresponding i n vpc  -COOEt hv  82  *COOEt  Eq 64  84  +  83  +  Other products  77  retention times to 82, 83, and 84_ were c o l l e c t e d by preparative vpc and found to have i d e n t i c a l s p e c t r a l properties  to 82_, 83, and 84_ formed  i n the sensitized photolysis of 7_9_ - 81. Additional support f o r structures 82, 83, and 84 came from t h e i r hydrolysis to the known dicarboxylic  acids.  The hydrolysis of j$2_ gave t r a n s , a n t i , trans-bicyclo [4.2.0] octane-7,8dicarboxylic a c i d , mp 180°-182° ( l i t . 83 afforded  7 7  mp 181°-182°)(Eq 65).  cis,trans-bicyclo[4.2.0]octane-7,8-dicarboxylic  Similarly,  a c i d , mp 197°-  C00H  k  82  NaOH H0  Eq 65  2  COOH  7 7 .  - 59 -  COOH Eq 67  NaOH H0  84  2  COOH  198° ( l i t .  7 7  mp 199°-200°) (Eq 66), and 84 gave c i s , a n t i , c i s - b i c y c l o [ 4 . 2 . 0 ] -  octane-7,8-dicarboxyxlic a c i d , mp 170-172  (lit.  mp 174 -176 ) (Eq 67).  c) Thermodynamic S t a b i l i t i e s of Photoproducts 82 - J35_ In order to e s t a b l i s h the structure proposed f o r photoproduct 85 which could not be obtained completely free of isomer 5_, i t was necessary to u t i l i z e the r e s u l t s of base catalysed epimerization experiments. I t 78 has been reported  that the dimethyl esters analogous to photoproducts  82 and 85_ epimerize under basic conditions to a mixture of the two with dimethyl ester 8_2 being favored.  A 50 : 50 mixture of 8>3_ and 85_ was  subjected to a c a t a l y t i c amount of sodium ethoxide i n absolute alcohol i n a sealed v i a l f o r 12 hrs at 80°. Four products, corresponding i n vpc retention times to j32, 83_, 84_, and 85_ were formed  (Eq 68). The r a t i o s of  82 : 85 and 83_ : 84 were 90 : 10 and 85 : 15 r e s p e c t i v e l y .  Compounds 82  .COOEt  83(50%)  COOEt N °Et > a  EtOH  .COOEt  85(50%)  COOEt  —I  8  2  ( 4 5 % ) + 83  (42.5%)  + 8 4 (7.5%) + 85 (5%)  Eq 68  - 60 -  COOEt 82 (87%)  +  85 (10%)  +  unknown  (3%) Eq 69  COOEt  82  COOEt NaOEt EtOH V  83  (86%)  +  84  (14%)  Eq 70  'COOEt  84 and 84_ prepared i n t h i s manner were i d e n t i c a l ( i r , nmr) to those previously observed.  Photoproduct 82, under s i m i l a r basic conditions gave an 87 : 10 : 3  r a t i o of three products (Eq 69).  The f i r s t was shown to be s t a r t i n g  material 8_2_ (vpc retention time, i r , nmr) and the second to be isomer 8_5 (vpc retention time and i r ) .  The t h i r d product was not i s o l a t e d .  Under  i d e n t i c a l conditions 84_ gave an 86 : 14 r a t i o of two products (Eq 70).  These  were shown by spectral data ( i r and nmr) and vpc retention times to be compounds 83_ and 84_ r e s p e c t i v e l y .  These r e s u l t s from the base catalysed  epimerization of 82_ (Eq 69) and 84_ (Eq 70)  c l e a r l y indicate that i n the  epimerization of the 50 : 50 mixture of 83_ and 85 (Eq 68) products 83 and 84 are produced from compound 83_ and compounds 82_ and 85_ are coming from compound 85_. product 85.  These conclusions confirm the structure proposed for photoThese r e s u l t s also established j32_ and 83_ as the most  thermodynamically stable isomers i n the trans and c i s series  respectively.  A d d i t i o n a l support for these s t a b i l i t y r e s u l t s came from the thermolysis of photoproducts 82,  83, and 84.  Diester 84 was heated i n a sealed tube  - 61 -  at  250 . After 28 hrs there was no change i n the 83_ : 84^ r a t i o of  81 : 19 (Eq 71). Both products were characterized by t h e i r s p e c t r a l  .COOEt  28 hrs  83 (81%) —  62 hrs  83 (82%) —  +  84 (19%)  Eq 71  84 (18%)  Eq 72  COOEt 84 .COOEt  83  COOEt  .COOEt 5 products i n following r a t i o s : 88 hrs  1.1(82) : 1.0 : 3.3 : 1.6 : 1.2 Eq 73  COOEt 82  properties ( i r , nmr) and vpc retention times.  These were the only two  products with the exception of d i e t h y l maleate and cyclohexene vpc retention times) present i n less than 1%.  (based on  Diester 83_ under i d e n t i c a l  conditions gave a mixture of 83 (82%) and 84 (18%) a f t e r 62 hrs (Eq 72). Diester j52_ i n i t i a l l y appeared to give the same products as i n i t s base catalysed epimerization (Eq 69) but a f t e r 88 hrs gave 5 products i n the r a t i o of 1.1 : 1.0 : 3.3 : 1.6 : 1.2 (Eq 73). The f i r s t of these was diester 82 (vpc retention time and nmr).  The others were not i d e n t i f i e d .  -  62  -  (3_) Discussion of Sensitized Photolyses of 79,  80,  and  81  a) Possible Mechanisms The equilibrium mixture of dienes 7_9, J50, sensitized  and 81_ formed i n the  (acetone, acetophenone) photolysis of compounds 7_9 and  80  indicate a c i s , t r a n s isomerization that i s f a s t e r than cycloaddition. the case of the photolysis of diene-diester 81_,  In  an equilibrium mixture of  _79 - £51 i s not reached as cycloaddition appears to be at least competitive with c i s to trans isomerization.  Thus i f the geometry of the double bonds  a f f e c t s the products formed, then one would i n t u i t i v e l y expect a d i f f e r e n t r a t i o of photoproducts i n the photolysis of j$l.  This i s i n fact shown to  be true experimentally. There are two general types of mechanisms usually postulated f o r 42  photochemical reactions.  The f i r s t involves a symmetry allowed process  r e s u l t i n g i n the s t e r e o s p e c i f i c formation of products v i a a concerted mechanism.  The second involves a two or more step process having d i s t i n c t  intermediates.  The intermediate may be d i r a d i c a l or i o n i c , and product  formation i s often non-stereospecific.  In order to determine what one  might expect from these two types of mechanisms i t would be h e l p f u l to predict the products from a simple 2 + 2  cycloaddition of two c i s - 1 , 2 d i 14  substituted ethylenes.  In the concerted cycloaddition  one would expect only products 86_ and 87_. products may  (Eq  74)  The r e l a t i v e y i e l d s of these  or may not be i n l i n e with t h e i r thermodynamic s t a b i l i t i e s .  More important i s the s t e r i c hindrance involved i n the geometry of approach of the two o l e f i n s .  In the stepwise mechanism (Eq 75)  one would  expect the same products 8j6 and 87_ plus the other four possible isomers  - 63 -  88, 89, 90, and 91.  I f the intermediates are s u f f i c i e n t l y long l i v e d the  products are usually formed i n amounts corresponding to their thermodynamic 18 79 stabilities.  Sometimes k i n e t i c control  '  i n the formation of the i n t e r -  mediate or of the product may be an important factor i n these reactions. Sometimes both concerted and stepwise mechanisms are operative i n the same 80 reaction  and detailed k i n e t i c data i s usually necessary to determine  how  large a part each mechanism contributes. In the cases of diene-diesters 79.» 80, and 81_ each are capable of photo2 2 chemically cycloadding i n a TT + TT fashion to give two products. Since s s 2 2 the o l e f i n s are i n a r e l a t i v e l y small a c y c l i c chain, TT + TT cycloaddition cl  appears to be s t e r i c a l l y u n l i k e l y .  3-  Diene-diester 7_9_ i s capable of giving i n  a concerted fashion cycloadded products 8_2_ and 8_4.  S i m i l a r l y , 8_0 and 8_1  - 64 -  Eq 76  Eq 77  Eq 78  can concertedly give r i s e to photoadducts 83 and _85 (Eq 77), and 92 and 93 (Eq 78) r e s p e c t i v e l y .  If t h i s were the only mechanism operative one would  expect a 46% y i e l d of 82 + 84, a 42% y i e l d of 83 + 85, and a 12% y i e l d of 92 and 93_.  These are based on the percentages of dienes 7_9, J30_, and 81_  present throughout the photolysis of 7J9 and 80.  In actual f a c t , however,  i n the photolysis of 79_ and 80, 78% of J32 + 84 and 22% of 83 + 85 are formed.  No 92 or 93_ i s ever found to be present even when pure 81_ i s  used as s t a r t i n g material.  In t h i s l a t t e r case an equilibrium mixture  - 65 -  of _79_ - 81_ was never achieved and thus a s i m i l a r p r e d i c t i o n of product d i s t r i b u t i o n s i s impossible.  Experimental evidence thus points away from  a concerted mechanism. In the case of a d i r a d i c a l or i o n i c mechanism there should be one intermediate for the formation of trans fused products 82_ and 85_  (94),  and another intermediate for the formation of c i s fused products j$3_ and  94 (e,e +  a,a)  95  (e,a) •» +,  84 (95).  or -  The formation of 94. and 95_ from the photolysis of 79 and 80  i s probably s t a t i s t i c a l products are formed. mations ( i . e . ,  i n nature as equal amounts of c i s and trans fused  Intermediate  94_ can e x i s t i n two d i f f e r e n t confor-  the e,e and a,a conformation).  Since bonding i s only  possible from the e,e conformation only t h i s w i l l be considered i n the following d i s c u s s i o n .  The e,a and the a,e conformations of  intermediate  95 are degenerate and thus only one of them need be considered.  Theoret-  i c a l l y 94_ can give r i s e to photoproducts 82_, 85_, and _93_ while intermediate 95 can bond to give 83_, 84_, and 92. considered  Each of these p o s s i b i l i t i e s w i l l be  separately. 81  Intermediate t r i p l e t 1,4  94_ may be regarded as a v i b r a t i o n a l l y deactivated  d i r a d i c a l which spin inverts to the singlet excited  and then bonds to form trans fused bicyclo[4.2.0]octane systems.  state As the  - 66 -  r a d i c a l s approach each other f o r bonding  ( i . e . , approaching the t r a n s i t i o n  s t a t e ) , non-bonded interactions are encountered between i n t e r a c t i o n ) , between C ^ Q and interaction).  (a,6), and between  and  (a,6  and C ^ Q (a,a  These interactions (Scheme 9) are expected to determine  Scheme 9  82  85  93  the r e l a t i v e amounts of the three possible trans fused bicyclo[4.2.0]octanes which are formed.  Formation of photoproduct 82_ involves no  adverse a,<5 or a,a interactions and would be expected to be formed i n greater amounts than isomers 85_ or 93.  Closure of 94_ to give both &5 and  93 involves two s t e r i c interactions (a,6 and a,a)  (Scheme 9) and the  e f f e c t of t h i s on t h e i r r e l a t i v e d i s t r i b u t i o n should depend on the magnitudes of the a,6 and a,a interactions as the t r a n s i t i o n state i s 79 approached  i n each case.  Previous work on the photolysis  of the  geometric isomers of dimethyl-2,7-nonadiene-l,9-dioate indicate that  - 67 -  a,6 e f f e c t s are stronger than a,a e f f e c t s as the 2,8 bond begins to form (Eq 79).  Photoproduct  98 whose formation from intermediate d i r a d i c a l 97  COOMe hv  COOMe .COOMe  i  Eq 79  +  COOMe  ^-^COOMe 96  ^COOMe  COOMe  COOMe 97  98  99  involves one a,a i n t e r a c t i o n , i s favored by a factor of three over photoproduct 99^, whose formation involves one a,6 i n t e r a c t i o n .  These r e s u l t s  tend to support the experimentally observed formation of photoproduct 85 (one a,6 and one a,a i n t e r a c t i o n ) i n preference to isomer 93_ ( two a,6 interactions).  Photoproducts  82 and 8_5 are formed i n a r a t i o of 6 : 1 and  none of isomer 93 was detected.  F o r t u i t o u s l y , the product r a t i o i s also  i n l i n e with the r e l a t i v e thermodynamic s t a b i l i t i e s of the various photoproducts.  Base catalysed epimerizations of 82_ (Eq 69) and 85_ (Eq 68), which  only involve avoidance of a,a i n t e r a c t i o n s , both give an 8_2 to 8_5 r a t i o of approximately 9 : 1 . Intermediate 95_ which i s the immediate precursor of the c i s fused 81 bicyclof4.2.0]octanes, can also be looked upon as a v i b r a t i o n a l l y relaxed t r i p l e t 1,4 d i r a d i c a l which spin inverts to the s i n g l e t state and then bonds.  The same type of non-bonded interactions (a,6 and a,a) are  involved i n the t r a n s i t i o n state as the d i r a d i c a l s t a r t s to bond (Scheme 10). Formation of photoproduct  £33_ involves one a,6 i n t e r a c t i o n while the  formation of isomer 84 involves one a,a i n t e r a c t i o n .  This i s very similar  - 68 -  to the formation of 99_ and 98_ respectively i n Eq 79. formation of photoproduct  On this b a s i s ,  84_ would be expected to be favored over formation  Scheme 10  of isomer J33_.  This was found to be true experimentally as the 84_ : J$3_  r a t i o i n the photolysis of ]9_ and 8 £ was approximately  2:1.  Formation  of isomer 92 involves two a,6 and one a,a i n t e r a c t i o n , and thus the a c t i v a t i o n energy f o r i t s formation would be expected r e l a t i v e to the formation of 83_ and  to be quite high  Experimentally, no 92_ i s observed.  The product r a t i o i n the formation of the c i s fused series i s not i n l i n e with the thermodynamic s t a b i l i t i e s of the products.  On treatment of 83_  or 84_ under base catalysed epimerization conditions or under thermolysis conditions the a,a interactions are avoided and the 83_ : approximately  r a t i o becomes  17 : 3.  It i s interesting to note that the mixed cycloadditions of d i e t h y l  - 69 -  and dimethyl maleate to cyclohexene are not governed by the same f a c t o r s as i n the photolyses of _79 and 80 and thus d i f f e r e n t product r a t i o s are observed  (Eq 80).  In these cases the a,a interactions are f a r more  important than a , 6 i n t e r a c t i o n s i n the closure of d i r a d i c a l species 100. The reason f o r the increased e f f e c t of the a,a i n t e r a c t i o n stems from the f a c t that the C^t Cg bond i s already formed and thus the C^ and C ^ Q groups  R00C>  a -~C00R  hv  I—^C00R R00C  100  a  R = Me or Et -C00R  00R  N  Eq 80 COOR  'COOR 12%  6%  28%(82)  0%  f e e l each other (a,a) more than the C^ and C ^ Q carbons as the Cg, C^ carbons begin to bond.  This explains the preference f o r trans  carboethoxy  groups i n both c i s and trans fused bicyelo[4.2.0]®etane systems (Eq 80). The preference f o r c i s fused bicyclo[4.2.0]octane products (R = Et, 72% c i s ; R = Me, 82% c i s ) can be attributed to the r e l a t i v e s t a b i l i t i e s of c i s 82 and trans fused bicyclo[4.2.0]octane systems. These arguments based on a k i n e t i c closure of d i r a d i c a l j)4_ and 95 explain the r e l a t i v e amounts of products j32 - 85_ formed i n the s e n s i t i z e d  - 70 -  photolysis of diene-diesters 7_9 and 80. Up u n t i l now,  the photolysis of diene-diester J51 has been ignored  for the most part.  This i s mainly the r e s u l t of the anomalous product  r a t i o that i s observed when pure 81_ i s used as a s t a r t i n g material.  The  major difference involves the preference f o r formation of c i s - b i c y c l o [4.2.0]octane systems over the corresponding trans fused systems.  Instead  of a c i s / t r a n s r a t i o of almost unity the photolysis of 81_ produces a r a t i o of almost 2 : 1 .  This change i s mainly brought about by the  increase of photoproduct 84_ and the decrease of photoproduct 82.  In order  to explain these r e s u l t s i n a s a t i s f a c t o r y manner i t would be necessary to propose a unique mechanism f o r the cycloaddition from the c i s , c i s isomer 81.  In the photolyses of 7_9_ and 80_, isomer 81_ i s only present to a maximum  of 12% and thus responsible f o r 12% of the f i n a l product mixture.  Thus i t  i s not too f a r wrong to consider the photolyses 79_ and 80_ as being separate from the photolysis of 81.  However, i n the photolysis of pure 81_ an  equilibrium mixture of diene-diesters i s never reached and 8_1_ i s always present as a major component i n the 7_9 - 8_1 mixture.  Since the product  r a t i o s are i n the same d i r e c t i o n as observed i n the photolyses of _79_ and 80 ( i . e . , j*2_ and 84_ are formed i n greater amounts than 8_5 and 8_3_ r e s p e c t i v e l y ) , then i t would seem l i k e l y that i n i t i a l bond formation i s the d i f f e r i n g factor operating.  A ground state complex such as that  shown i n 101 would favor the formation of 9_5 and hence lead to more c i s fused products.  It i s also conceivable that an excited state complex  of s i m i l a r geometry could be formed i n the photolysis of the c i s , c i s isomer  - 71 -  COOEt COOEt  T  / COOEt  \COOEt 102  101 81.  This argument, based on exciplex formation, i s analogous to Corey's 13  explanation  f o r the s t e r e o s p e c i f i c photocycloaddition of cyclohexenone 27  to methoxy ethylene (Eq 21) and White's reasoning of photocycloaddition i n 3-farnesene (Eq 30).  f o r the d i r e c t i o n  While such a complex (101)  explains the r e s u l t s , the reason for such a complex i s unclear.  Molecular  model i n v e s t i g a t i o n does not indicate any obvious preference f o r a conformation such as that i n 101 over a complex such as that i n 102 which would lead to the trans intermediate 94_.  As can be seen, a simple  explanation f o r the preference f o r c i s fusion i n the photolysis of diene—diester 8_1 i s not available at present.  It i s s t i l l f a i r l y certain  however that the photolysis of 81_ i s proceeding v i a a t r i p l e t  diradical  intermediate as i s the case for the photolyses of 7_9_ and 80. b) I n i t i a l Bond Formation There have been many attempts to explain the s e l e c t i v i t y of the i n i t i a l bonding step i n photochemical cycloadditions of a c y c l i c and c y c l i c non-conjugated dienes.  Each of these explanations possesses c e r t a i n  merits i n i n d i v i d u a l examples, but usually cannot be extended to other systems.  The most widely used guide to these cycloadditions i s that a  f i v e membered r i n g i s formed f i r s t .  This was proposed by Srinivasan and  16 Carlough  and i s better known as the "rule of f i v e " .  While t h i s mnemonic  - 72 -  does indicate the d i r e c t i o n of cycloaddition i n 1,4- 1,5- and 1,6 dienes, i t i s inapplicable i n the case of 1,7 dienes.  Furthermore, i t i s  s t r i c t l y empirical and does not indicate why f i v e membered ring formation should be preferred. An often used explanation f o r the d i r e c t i o n of cycloaddition i s based on the supposition that i n i t i a l bond formation occurs i n such a way as to produce the most stable d i r a d i c a l intermediate.  At f i r s t  glance i t could be argued that the photolyses of diene-diesters 79, 80, and 81_ are best described i n this manner.  Intermediate 103 (mixture of  94 and 95) would be expected to be more stable due to the influence of the 32 carboethoxy  groups  than intermediates 104 or 105 (Eq 81). There are two  COOEt  •.  COOEt  104 H  COOEt 82 - 85  79, 80, or 81  COOEt H  103 (94 + 95) :00Et  lOOEt 105  Eq 81  - 73 -  factors which mitigate against t h i s r a d i c a l s t a b i l i t y argument.  Recently,  the importance of the s t a b i l i z i n g influence of the carbonyl group on an a r a d i c a l (103) has been cast i n doubt by the work of King, Golden,  and  83 Benson.  Thermal studies on the bromination of acetone indicate that  there i s no s t a b i l i z a t i o n i n the acetonyl r a d i c a l (106).  0  0  I  II  CH -C-CH «  CH -C=CH  106  107  3  This indicates  2  3  2  that structure 107 does not contribute toward the s t a b i l i t y of 106.  There  i s a s t a b i l i z a t i o n energy of 2.7 kcal/mole i n going from the acetonyl to the methyl acetonyl r a d i c a l but t h i s change i s i n l i n e with the s t a b i l i z a t i o n 19 gained i n going from a primary to a secondary r a d i c a l .  These studies  indicate that there should be very l i t t l e difference among the s t a b i l i t i e s of the d i r a d i c a l s 103, 104, and 105.  Secondly, while a few  photochemical  cycloadditions (e.g., myrcene (Eq 29) and isogermacrone(Scheme 6)) proceed through the formation of t h e i r most stable d i r a d i c a l intermediates most c y c l i z a t i o n s do not.  hv  1 X = 0 or  This i s e s p e c i a l l y so i n the case of 1,5 dienes (Eq 82).  CH  2  »  \  /  >  /  T  \  Eq82  - 74 -  Other systems such as cyclooctadiene (Scheme 2) and  cyclodeca-3,8-diene-  1,6-dione (Eq 51) are capable of i n i t i a l bond formation to give two d i r a d i c a l s which do not d i f f e r s i g n i f i c a n t l y i n s t a b i l i t y and yet i n the case of cyclooctadiene only "crossed" cycloaddition occurs while " s t r a i g h t " c y c l i z a t i o n occurs e x c l u s i v e l y for dione.  cyclodeca-3,8-diene-l,6-  The above observations tend to r u l e out the v a l i d i t y of using  r a d i c a l s t a b i l i t y to explain the d i r e c t i o n of cycloaddition i n the photolyses of the geometric (79  isomers of d i e t h y l  2,8-decadiene-l,10-dioate  81). Another possible explanation for the d i r e c t i o n of i n i t i a l bond  formation i n the photolyses of 7_9_, 8_0, and 81_ may  be obtained by  observing the mode of addition of the t r i p l e t state of an a,3-unsaturated carbonyl species to an o l e f i n .  I n i t i a l e x c i t a t i o n followed by d e r e a l i z a -  t i o n produces an intermediate d i r a d i c a l species which possesses a r a d i c a l 84 centre on  (Eq 83 - 85) and a r a d i c a l centre on the carbonyl oxygen.  The r a d i c a l centre at  i s now  to the ground state o l e f i n . photochemically  capable of adding intramolecularly  I n i t i a l bonding by the 3 carbon (C^) of a  excited a,3-unsaturated carbonyl species has been recently  hv  Eq 83 COOMe  108  109  - 75 -  Is^vrCOOMe  1  •OMe hv  ^COOMe  a  \b I \ l \  Eq 84  1  s^N^vCOOMe  110  96  0  COOEt  ^^OEt  hv j\b  -COOEt  Eq 85  COOEt 111  (79 - 81) 85 established by the work of D i l l i n g pentenone to 1,2-dichloroethylene.  on the mixed cycloaddition of c y c l o 90 79 76 Experimentally,  '  '  the r a d i c a l  centre on C^ i n d i r a d i c a l s 109, 110, and 111 c y c l i z e at the o l e f i n centre v i a path b_ ( f i v e membered r i n g formation), path a_ ( f i v e membered r i n g formation), and path a_ (six membered ring formation) r e s p e c t i v e l y . These c y c l i z a t i o n s ( i . e . , v i a path a_ or b) can be compared to the ground state intramolecular addition of a free r a d i c a l to an o l e f i n i c centre (Scheme 11).  When n (the number of carbon atoms separating the  free r a d i c a l centre from the o l e f i n centre i n 112)  86  i s equal to 2, J u l i a  states that there i s r e l a t i v e l y poor overlap between the free r a d i c a l centre and the o l e f i n centre i n both path a_ and path b_ c y c l i z a t i o n s . Experimentally, t h i s i s supported by the fact that c y c l i z a t i o n of 87—89 4-pentenyl free r a d i c a l s (n = 2) i s only a minor r e a c t i o n pathway compared to competitive intermolecular reactions. When c y c l i z a t i o n does  - 76 -  Scheme 11  (CH ) 9  path a.  \ (CH )  \b \  n  \ \  112  ath b (CH ) 2  R„  n  R-,  (For X, Y, R , R , and n-See Table 3) 2  114  2  87 88 occur  '  (Table 3 ) .  exclusive f i v e membered r i n g formation (path b) i s observed C l a s s i c a l l y , p r e f e r e n t i a l path b_ c y c l i z a t i o n can be r a t i o n -  a l i z e d on the basis of the r e l a t i v e r a d i c a l and thermodynamic s t a b i l i t i e s of the species involved i n path a_ and path b_ c y c l i z a t i o n s (Scheme 11). These r e s u l t s f o r 4-pentenyl free r a d i c a l s c l o s e l y p a r a l l e l those of the photochemical intramolecular addition of 109 (Eq 83). 90 only f i v e membered r i n g formation  Photochemically,  ( i . e . , "crossed" cycloaddition,  path b)  i s observed. 86 89 When n = 4, molecular model investigations  '  of o r b i t a l s f o r path a_ and poor overlap f o r path b_.  indicate good overlap This indicates  that  s i x membered ring formation (path a) should be favored over seven membered r i n g formation (path b ) .  Furthermore, thermodynamic s t a b i l i t y  of the s i x membered r i n g and p r o b a b i l i t y factors governing the c y c l i z a t i o n  - 77 -  of the r a d i c a l both tend to favor path a_.  Experimentally,  6-heptenyl  free r a d i c a l s c y c l i z e intramolecularly to give p r e f e r e n t i a l l y membered r i n g formation (path a ) . this cyclization ( i . e . ,  86 89 '  six  The photochemical analogue of  c y c l i z a t i o n of 111)  gives products i n d i c a t i v e  of an exclusive path a mechanism ( " s t r a i g h t " c y c l o a d d i t i o n ) . The c y c l i z a t i o n of 5-hexenyl free r a d i c a l s i simple a picture as when n = 2 or 4 (Table  76  (n = 3) does not present 3).  Here molecular models  Table 3_ n  X  Y  1  H  H  2  H  H  2  CN  2  Path a(%)  Path b(%)  R<  *1  *2  H  H  0  0  88  H  H  0  14  88  COOEt  H  Me  0  30  87  CN  COOEt  H  H  0  0  87  2  H  H  H  H  0  0  89  3  H  H  H  H  43  0  89  3  H  H  H  H  84  8  88  3  H  H  H  H  90  3  23  3  CN  COOEt  H  H  16  84  86  3  H  COOEt  H  H  44  56  86  4  H  H  H  H  49  trace  88  4  CN  COOEt  H  H  34  •  86  0  86 89 indicate good overlap o l e f i n moiety.  '  of the free r a d i c a l with both centres of the  Based on the thermodynamic s t a b i l i t i e s of the products  formed (cyclohexane v s . methylcyclopentane) of the intermediates  and on the r a d i c a l  stabilities,  (cyclohexyl r a d i c a l v s . the cyclopentylmethyl radical)  one would expect six membered ring formation to predominate (path b ) . Experimentally, however, just the opposite has been found to be true.  The  - 78 -  work of Brace  21  on the treatment of 1,6-heptadiene with iodoperfluoro-  propane (Rpl) leads exclusively to cyclopentane formation (Eq 86). He 89 o f f e r s no explanation f o r the generality of these reactions.  Walling  has found that the reaction between 5-hexenyl mercaptan and t r i e t h y l phosphite r e s u l t s i n p r e f e r e n t i a l methylcyclopentane formation (Eq 87). CH R ^CH i R I Eq 86 2  F  2  F  +  Eq 87  P(OEt).  0% at 60°  43% at 60°  3% at 120°  50% at 120°  84% d i - t - b u t y l peroxide  s  "Ph  Eq 88 8%  Only when he raises the temperature of the reaction from 60° to 120° does he f i n d any cyclohexane formation.  He comments on the fact that there  i s l i t t l e difference i n the s t e r i c requirement f o r closure at  (path a_)  or at Cg (path b) and indicates that formation of methylcyclopentane i s  - 79 -  probably k i n e t i c i n nature.  Further evidence f o r t h i s s i m i l i a r , unique 88  behaviour of 5-hexenyl free r a d i c a l s comes from the work of Pines the treatment of l-phenyl-6-hexene with di-t-butylperoxide.  on  Here (Eq 88)  some cyclohexane formation occurs but i t i s very minor compared to the amount of methylcyclopentane formed.  I f , as indicated i n the above  examples (Eq 86 - 88), the free r a d i c a l c y c l i z e s k i n e t i c a l l y then the formation of the cyclohexyl and the cyclopentylmethyl r a d i c a l must be irreversible.  This has been shown to be true as the thermal decomposition  of di(cyclohexyl-formyl) peroxide and d i ( c y c l o p e n t y l - a c e t y l ) peroxide 23 give only cyclohexane and methyl cyclopentane r e s p e c t i v e l y . There are several examples, when the free r a d i c a l i s highly s t a b i l i z e d , that s i x 22 86 91 membered r i n g formation i s preferred (Scheme 12). ' ' These r e s u l t s Scheme 12  X = CN, Y = COOEt or X = Y = COOEt  - 80 -  have been explained by J u l i a to be due to the r e v e r s i b l e formation of the cyclohexenyl and cyclopentylmethyl r a d i c a l s , followed by i r r e v e r s i b l e 91 product formation (Scheme 12).  Such an explanation would tend to  favor the most thermodynamically stable product ( i . e . , cyclohexane formation, path b_).  Thus thermodynamic control replaces k i n e t i c control  when the free r a d i c a l i s s t a b i l i z e d .  In order to support h i s scheme f o r  the r e v e r s i b l e path a_ and path b_ c y c l i z a t i o n s (Scheme 12), J u l i a thermolysed the appropriately substituted (R^ = CN and  =  COOEt - Scheme 12) t e r t i a r y -  butyl cyclohexyl performate and t e r t i a r y - b u t y l cyclopentyl peracetate, and found that they both gave mixtures of cyclohexane and methyl cyclopentane products.  The s i m i l a r i t y between the c y c l i z a t i o n of 5-hexenyl free  r a d i c a l s and photocyclization of the 1,6 dienes 96_ probably l i e s i n the k i n e t i c closure to form a f i v e membered r i n g v i a path a_. 18 shown by L i u and Hammond formed i r r e v e r s i b l y .  I t has been  that t h e i r intermediate d i r a d i c a l (11) i s  There i s no reason to expect that the c y c l i z a t i o n  of 110 (Eq 84) would be r e v e r s i b l e .  Experimentally 110 (photochemically  excited 96) c y c l i z e s exclusively v i a path a_ to form " s t r a i g h t " addition j . 79 products. It can be concluded that both ground state and photochemical i n t r a molecular c y c l i z a t i o n s of alkenyl free r a d i c a l s 112 (n = 2 and 4) proceed i n a manner expected on the basis of the r a d i c a l and thermodynamic s t a b i l i t i e s of the species involved.  However, f i v e membered ring formation  i n the c y c l i z a t i o n of 5-hexenyl free r a d i c a l s (n = 3, 112) and i n the analogous photochemical c y c l i z a t i o n s (Eq 84) i s proceeding v i a a k i n e t i c closure.  The reason for such a closure i s not immediately clear but i t 91 has been suggested that entropy factors may play a major part.  - 81 -  A f i n a l highly speculative explanation for the d i r e c t i o n of i n i t i a l bond formation i n photochemical cycloadditions i s based on the p o s s i b i l i t y that the f i r s t step i s controlled by the symmetry of the highest occupied molecular o r b i t a l .  If a n  2 2 + TT geometry of approach of the o l e f i n s i s s s  assumed then the mixing of their bonding  (TT^ ± TT^) and antibonding  ( i r ^ * ± T ^ * ) o r b i t a l s (Fig 5) w i l l produce a set of four new molecular o r b i t a l s .  non-degenerate  If e x c i t a t i o n occurs, the highest occupied molecular  o r b i t a l (ijO predicts that the f i r s t step should proceed i n a " s t r a i g h t "  manner.  Such a molecular o r b i t a l approach explains the d i r e c t i o n of  cycloaddition i n 1,4-  1,6- and 1,7- dienes but f a i l s to explain "crossed"  cycloaddition i n 1,5 dienes (Eq 89 ).  If the o r b i t a l s of the 3,4 sigma  bond i n 1,5 dienes were mixed with the four molecular o r b i t a l s ty - ty.  - 82 -  Eq 89  derived above then a possible crossing of the energy l e v e l s of ty^ and IJ^ and  and  may  occur.  Cookson (See Introduction) has done a s i m i l a r  mixing of the c e n t r a l sigma bond i n order to explain the Cope rearrange35 ment of 1,5 dienes.  If the mixing of the sigma bond i s s u f f i c i e n t l y  large and l e v e l changing does occur then the highest occupied molecular o r b i t a l i n the excited state i s \p. (See F i g 3) and t h i s predicts that  "crossed" i n i t i a l bonding should occur.  These ideas of through-bond  92 coupling are not unique as Hoffmann t h i s topic s p e c i f i c a l l y .  has published a paper dealing with  The a p p l i c a t i o n of through-bond coupling to  1,5 dienes, however, i s very speculative and many factors such as d i f f e r e n t geometries  of approach i n the t r a n s i t i o n state, non-coplanarity of the  sigma and p i systems and s t e r i c interactions probably render such an explanation inconclusive.  It i s hoped that future studies i n photoelectron  - 83 -  spectroscopy w i l l be able to determine the extent of through-bond interactions on the d i r e c t i o n of photocycloaddition of 1,5 dienes.  (4) Direct I r r a d i a t i o n of Compounds 79, 80, and 115 a) Photolysis of 79 Photolysis of _79 i n either methanol or hexane under Corex optics led to a complex mixture of photoproducts 19_, 8>0, {51_, 115, 116, and 117. Continued i r r a d i a t i o n led exclusively to the formation of 117.  As  indicated by a n a l y t i c a l vpc, photoproducts jK), 81_, 115, and 116 b u i l d up i n i t i a l l y and then disappear i n accordance with Scheme 13.  Compound 7j)  decreases throughout and photoproduct 117 increases throughout.  Vpc  Scheme 13 COOEt  COOEt  COOEt COOEt  COOEt indicates an obvious induction period f o r the formation of 117 and a less obvious one f o r 115 and 116.  - 84 -  b) Characterization of Photoproducts 79 - 81 and 115 - 117 Characterization of the photoproducts was made on the basis of t h e i r nmr and i r spectra as given i n Table 4.  The geometries of the various  double bonds were indicated by c h a r a c t e r i s t i c double bond i r stretches at 10.04 - 10.27 u (trans double bond CH out of plane deformation) and 11.93 - 12.04 y ( c i s double bond CH out of plane deformation), while the positions of the double bonds could be determined by the infrared carbonyl stretching frequencies of 5.74 - 5.79 y (g,y-unsaturated ester) and 5.81 5.83 y (a,3-unsaturated e s t e r ) .  Furthermore the geometry of the double  Table 4 Compound  79  80  81  115  116  117  Double Bond P o s i t i o n and Geometry  CH=CH Coupling Constants (Hz)  IR Double Bond C-H Rock (y)  IR C=(  trans-a,3  15.5  10.15  5.81  trans-a,g  15.5  10.15  5.81  trans-a,3  15.5  10.04  5.81  cis-a,3  11.5  11.97  5.81  cis-a,8  11.6  12.04  5.82  cis-a,3  11.6  12.04  5.82  trans-a,3  15.4  10.18  5.82  trans-3,y  mult  10.18  5.79  cis-a,3  11.5  11.93  5.83  trans-3,y  mult  10.14  5.79  trans-3,y  mult  10.27  5.74  trans-3,Y  mult  10.27  5.74  bonds i n the case of the a,3-unsaturated esters was indicated c l e a r l y by nmr.  The 3 proton always appeared as a doublet of t r i p l e t s with a coupling  -  constant of 15.5  85  -  (trans double bond) or 11.5  Hz  Hz  ( c i s double bond).  a v i n y l hydrogen appeared as a doublet with small a l l y l i c The v i n y l hydrogens of the B,Y unsaturated _  (1.5  The  Hz) coupling  double bonds were complex  m u l t i p l e t s and a s h i f t reagent was used i n order to determine the geometry 93  of  the double bonds i n 117.  i n a CCl^ solution of 117  The use of tris(dipivalomethanato)europium  caused  the equivalent  and Cg v i n y l hydrogens  to appear as two d i s t i n c t t r i p l e t s with a t y p i c a l trans v i n y l coupling constant of 15.7  Hz.  This value could also be obtained from the broad  doublet responsible f o r the C^ and C^ v i n y l hydrogens.  These assignments  were supported by decoupling experiments (See Experimental). Further proof of structure for photoproduct J50 came from an independent synthesis "* while the structure of 117 7  was v e r i f i e d by hydrolysis to the  94  known  trans,trans-deca-3,8-diene-l,10-dicarboxylic acid which was  identical  95  to an authentic sample.  We  thank Dr. C h i u s o l i f o r a generous sample of  trans,trans-deca-3,8-diene-l,10-dicarboxylic a c i d . F i n a l l y , a n a l y t i c a l analyses were obtained on the unknown compounds 81,  115,  and 116 which supported  t h e i r isomeric structures. Mass s p e c t r a l  fragmentation patterns of the photoproducts  are i n agreement with the  structures presented i n Scheme 13. c) The Photolysis of 80 and Scheme 13 was 115.  115  further supported by the d i r e c t photolysis of 8_0 and  Diene-diester 80_ led to photoproducts  81,  115,  being the sole product a f t e r extended i r r a d i a t i o n . appearance of 79 observed. gave compound 116,  116,  and 117 with  At no time was  On photolysis, trans,trans-diester 115  117  the initially  and a f t e r an observable induction period, compound  117.  - 86 -  Compound 117 was  the only product a f t e r continued photolysis.  At  no  time i n the photolysis of 115 were compounds 7_9 - 8JL observed. d_) Quenching  Studies  Photolysis of 79_ (0.001 moles) i n hexane i n the presence of varying amounts of piperylene  (0.005 moles, 0.05  moles, and  a mixture of products i n accord with Scheme 13. was,  however, greatly a f f e c t e d .  present the longer  The  0.2  The  moles) led to  time for the photolyses  larger the amount of  piperylene  i t took for deconjugation to occur.  (5) Discussion of the Direct I r r a d i a t i o n of Compounds 79, 80, and  115  Photodeconjugation of an a,6-unsaturated ester to the corresponding $,Y unsaturated ester i s a f a i r l y w e l l documented reaction (See -  Introduction).  The most generally accepted mechanism involves trans to c i s isomerization followed by y hydrogen abstraction by the n,ir* excited s i n g l e t state of the ester carbonyl. ketonize The  The r e s u l t i n g d i r a d i c a l forms a dienol which can  to give the observed 3>Y  isomer.  intermediacy of the c i s o l e f i n i n the photodeconjugation of 79  i s , i n general, indicated by Scheme 13 and photolysis of 115.  i n p a r t i c u l a r , by  Direct i r r a d i a t i o n of 115 gives at f i r s t 116 and  a f t e r an induction period deconjugated product 117. that the c i s (a,6),trans (3,Y) isomer 115  the  These r e s u l t s i n d i c a t e  isomer 116 and not the trans  i s the immediate precursor  of 117.  The  (a,3),trans  excited state  responsible for the deconjugation observed i n the i r r a d i a t i o n of 79, 62 and  115  i s the  n,Tr*  s i n g l e t state.  then  80,  6A '  The assignment of the excited  state i s supported by photolysis experiments under Corex optics where  (3,Y)  - 87 -  only the  n,Tr*  absorption band of the a,3-unsaturated ester i s absorbing 76  light.  The m u l t i p l i c i t y i s supported by the s e n s i t i z a t i o n  quenching studies.  and  T r i p l e t s e n s i t i z a t i o n f a i l e d to give any deconjugation.  Under these conditions only cycloadded product formation was observed. Quenching experiments with piperylene f a i l e d to prevent photodeconjugation from occurring.  With larger amounts of piperylene present the rate of  the deconjugation was slower but t h i s could be due to a slower rate of trans to c i s isomerization.  The rate of photodeconjugation i s f a s t e r  than c i s to trans isomerization as no 79_ i s observed i n the d i r e c t i r r a d i a t i o n of 80. Unique to t h i s system i s the fact that only the di-3,y-trans,trans isomer 117 i s formed i n the deconjugation of 79, 80, and 115.  Other authors  have found a much less preference f o r the formation of the trans 3,y 59 isomer (See Introduction).  These r e s u l t s may be explained by the  mechanism presented i n Scheme 14.  Trans to c i s isomerization of 79  Scheme 14  120  121  - 88 -  followed by y hydrogen abstraction by the h a l f - f i l l e d n - o r b i t a l on oxygen i n the  n,Tr*  s i n g l e t state (118) leads i n i t i a l l y to a species  119.  This could then undergo r o t a t i o n about the 3,Y~carbon carbon bond to give either the c i s (120) or the trans (121) d i e n o l . be the most favored on s t e r i c grounds. as only the trans deconjugated product  The l a t t e r would  This i s supported  experimentally  i s observed.  These r e s u l t s point out the possible synthetic u t i l i t y of such a deconjugation  process.  Almost any di-3,y-unsaturated ester of s p e c i f i e d  chain length and known geometry can be prepared  i n t h i s manner.  (6) Conclusion Like 3,y-unsaturated  ketones, the photolysis of a c y c l i c 1,7  diene-  d i e s t e r s (79, 80, and 81) show unique properties under d i r e c t and s e n s i t i z e d conditions.  In the presence of t r i p l e t s e n s i t i z e r s  1,7-  dienes cycloadd i n a " s t r a i g h t " manner to give a mixture of c i s and fused bicyclo[4.2.0]octanes.  Under d i r e c t i r r a d i a t i o n ,  occurs to give e x c l u s i v e l y the trans,trans isomer  117.  trans  photodeconjugation  - 89 -  C.) Cyclonona-2 ,6-dienone A l i t e r a t u r e survey of the photochemistry of c y c l i c dienes (See Introduction) quickly demonstrates  non-conjugated  the tendency of the dienes  to give cycloaddition products i n d i c a t i v e of i n i t i a l five-membered r i n g formation.  1,5-Cyclooctadiene  (Scheme 2) and isogermacrone  (Scheme 6) are  t y p i c a l examples of 1,5- and 1,6 dienes respectively, which photochemically cycloadd i n t h i s manner.  Perhaps due to synthetic d i f f i c u l t i e s , homologous  c y c l i c dienes ( i . e . , 1,4-cycloheptadiene;  1,5-cyclononadiene;  1,6-cyclo-  48 58 undecadiene;  etc.) have received very l i t t l e attention.  c y c l i c dienes, 1,5-cyclononadiene  '  Of these  (122) possesses the unique property of  being able to photochemically cycloadd v i a i n i t i a l five-membered ring formation to give both " s t r a i g h t " and "crossed" addition products (Scheme 15). Scheme 15 H  H II  122  Straight II  or  it Crossed I I  - 90 -  The photochemistry of 122 could shed some l i g h t on the mechanism of cycloaddition i n non-conjugated dienes depending on whether  "straight"  or "crossed" product formation predominated. Based on t h i s unusual property of cyclononadiene i t was decided that such a skeleton would become the basis of a photochemical i n v e s t i g a t i o n . Compound 122 i s i n i t s e l f a poor choice for such an i n v e s t i g a t i o n as i t s u l t r a v i o l e t absorption region i s not e a s i l y accessible by conventional l i g h t sources.  It was decided then that 2-bromo-cyclonona-2,6-dienone  and cyclonona-2 6-dieneone (128) would make good s t a r t i n g materials. >  (126), These  choices were based on a possible synthetic scheme (Scheme 16) and on the Scheme 16  B  r  Br  - 91 -  fact that the carbonyl has an e a s i l y accessible u l t r a v i o l e t absorption region.  Scheme 16 outlines the synthetic approach taken to obtain  ketones 126 and 128. Cyclooctadiene was converted to 9,9-dibromo-bicyclo99  [6.1.0]non-4-ene (123) by the method of SkattebAl.  Compound 123 was  then subjected to a A g assisted a c e t o l y s i s by s t i r r i n g i t i n a s o l u t i o n +  of s i l v e r acetate i n a c e t i c acid f o r two days. This r e s u l t s i n the s t e r e o s p e c i f i c ^ " ^ formation of 2-bromo-3-acetoxy-cis,trans-cyclonona-1,6diene (124) This was e a s i l y converted to the alcohol (125) by a l k a l i n e hydrolysis of the acetoxy group.  Many attempts to oxidize alcohol 125  -,u various • -A• «. / T with oxidizing reagents (e.g., Jones,  1  Comforth,^^ fruitless.  0  2  Browns,103 _C o... l l i n s104  i,  AgO, and Mn02^^) to the corresponding ketone proved  Equimolar mixtures of oxidizing reagent and alcohol usually  returned s t a r t i n g material unreacted, while excesses of reagents produced inseparable complex mixtures of products.  The f a i l u r e of the oxidation  of 125 could be due to the influence of the bromine group.  In order to  test t h i s hypothesis the removal of the bromine was carried out by s t i r r i n g alcohol 125 i n an excess of sodium i n l i q u i d gave i n good y i e l d trans,cis-2,6-dienol (127).  ammonia.This  Several attempts (MnO^,  Browns oxidation, and C o l l i n s oxidation) at oxidizing 127 to the corresponding ketone also f a i l e d .  Some encouraging r e s u l t s have been obtained  with the use of Jones reagent although the y i e l d of product suspected to be ketone 128 i s quite low (<10%).  Work at characterizing t h i s product  and at improving i t s y i e l d i s presently underway.  - 92 -  EXPERIMENTAL  A) General Procedures Infrared ( i r ) spectra were obtained, unless otherwise stated, on neat l i q u i d samples between sodium chloride plates with a Perkin-Elmer 137 spectrophotometer.  Nuclear magnetic resonance  (nmr) spectra were recorded  by Miss P. Watson and Mr. R. Burton on the following spectrophotometers: Varian Model A-60, T-60, and HA-100, and Jeolco C-60H. tetramethylsilane was used as an i n t e r n a l standard.  In a l l cases  Mass spectra were  obtained on a d i r e c t i n l e t AEI MS-9 instrument at 70 eV, and u l t r a v i o l e t spectra were recorded on a Unicam SP-820 spectrophotometer.  Melting points  were taken on either a Thomas-Hoover (TH) c a p i l l a r y apparatus or a F i s h e r Johns (FJ) melting point block and are corrected unless otherwise indicated.  Elemental analyses were performed by the departmental micro-  analyst, Mr. P. Borda.  Vapour phase chromatography (vpc) was carried out  on either a Varian-Aerograph 90-P3 or a Varian Aerograph Autoprep Model A700.  Both were connected to Honeywell Electronik 15 s t r i p chart recorders.  The c a r r i e r gas i n a l l cases was helium.  The following a n a l y t i c a l (A -  5' x 1/4") and preparative (P - 20' x 3/8") columns were used: on 60/80 Chromosorb W A/W DMCS, (column A - l ) ; W, (column A-2);  20% SE-30  20% DEGS 60/80 Chromosorb  10% Carbowax 60/80 Chromosorb W, (column A-3);  60/80 Chromosorb W, (column A-4);  10% FFAP  30% SE-30 45/60 Chromosorb W, (column P - l ) ;  30% DEGS 45/60 Chromosorb W, (column P-2); and 30% Carbowax 45/60 Chromosorb W, (column P-3).  The column temperature  (°C) and the helium  flow rate (ml/min) are given i n parenthesis a f t e r the column stated.  - 93 -  Thin layer chromotography  ( t i c ) was carried out on plates coated with  E. Merck and Co. S i l i c a Gel G. for column chromotography.  Grace (activated) S i l i c a Gel was used  Large scale photolyses (internal) were  carried out i n a water-cooled Quartz immersion w e l l apparatus.  Small  scale photolyses (external) were performed by placing the s o l u t i o n to be photolysed i n a 50 ml Quartz tube and strapping t h i s to the outside of the water-cooled immersion w e l l .  In either case, a Hanovia 450 W type L  lamp with a Pyrex, Corex, or Vycor f i l t e r was used.  A l l solvents were  d i s t i l l e d , the methanol being d i s t i l l e d from a s o l u t i o n of sodium and dimethyl p h t h a l a t e . ^  methoxide  A l l organic reagents used were reagent grade  unless otherwise indicated.  Photolysis solutions were degassed p r i o r to  i r r a d i a t i o n with Canadian Liquid A i r argon or L grade nitrogen.  B)  Isogermacrone Source of Germacrone (68).  The author i s indebted to Dr. M. Suchy,  Czechoslovak Academy of Science, and to Fritzsche Brothers, Inc., New York, N.Y.  for generous samples of J>8_.  In the l a t t e r case, i t was  necessary to i s o l a t e germacrone from Zdravetz o i l .  The contents from a  one ounce b o t t l e of zdravetz o i l were f i l t e r e d to y i e l d 2.2 g of crude yellow c r y s t a l s , mp 50-53" uncor.  One r e c r y s t a l l i z a t i o n from methanol  (15 ml) yielded 1.9 g of needle-like white c r y s t a l s of 68, mp 55 —55.5 uncor ( l i t . ^ ^ 55.5°-56°).  A small amount of t r i a c o n t a i n e , ^ mp 66° was  present as an impurity and could be e f f e c t i v e l y removed by e l u t i o n on S i l i c a Gel with hexane.  Germacrone i s o l a t e d i n t h i s manner had the  following s p e c t r a l c h a r a c t e r i s t i c s :  uv max  (MeOH) 246 nm;  i r (CHC1,)  - 94 -  5.97  (C=0), and sh 6.02  (C=C) u; nmr  v i n y l H), 6.55-7.33 (m, 4, C 8.23  (s, 3, C  8.60  (s, 3, C^  1 4  2  CH ), 8.30  and C  (s, 3, C  3  CH ) .  2  (CC1.) T 4.45-5.00 (m, 2, C. and C CH ), 7.88  g  2  1 5  CH ), 8.42 3  (broad s, 4, C (s, 3, C  5  and C  g  0  CH >, 2  CHg), and  These spectra are i n f u l l agreement with those  reported by V. G. O h l o f f .  6 6  Synthesis of Isogermacrone.  A s o l u t i o n of germacrone (1.92 g,  0.0088 mole) i n 50 ml of ethanolic 0.5 N potassium hydroxide was refluxed under nitrogen for 4 hrs. A f t e r t h i s period, t i c (10% ether-benzene) indicated the presence of s t a r t i n g material and one new product; the l a t t e r being the most intense spot under iodine development.  The solvent was  removed i n vacuo and the residue neutralized with 5% aqueous hydrochloric acid.  The mixture was then extracted with chloroform (3 x 50 ml).  The  combined chloroform extracts were washed with water (2 x 50 ml) and dried (sodium s u l f a t e ) .  The chloroform was removed i n vacuo to y i e l d  approximately 2 g of clear o i l .  Vpc column A-1 (200°, 60 ml/min) indicated  the presence of four products, isogermacrone being the major one. P u r i f i c a t i o n by column chromatography afforded 0.550 g of 60-80% pure isogermacrone (benzene as eluant), and 1.30 g of 90-95% pure isogermacrone (5% ether-benzene as eluant).  Purity of chromatography fractions was  determined by vpc column A-1 (200°, 60 ml/min).  C r y s t a l l i z a t i o n of the  clear o i l , obtained from column chromatography, from methanol gave white c r y s t a l s , mp 48°-50° uncor ( l i t . ^ 51°-52°). following s p e c t r a l c h a r a c t e r i s t i c s : ir  (CHC1 ) 6.00 3  v i n y l H), 4.82  (C=0), and 6.14  uv max  (C=C) u; nmr  Isogermacrone exhibited the (hexane) 203, 252, and 330 nm; (CDC1 ) x 3.99 3  ( t , 1, Cg v i n y l H), 6.82-7.20 (m, 2, C  g  (s, 1, C  2  CH ), 7.40-8.60 2  - 95 -  (m, 6, C , C , and C 4  C  15  C H  3^'  5  a n d  8  "^  CH ) , 8.19  g  >  8  (d, 3,  2  3  C  i 2 3^* CH  T  n  e  s  CHg) , 8.32  (m, 6, C  and  s p e c t r a l c h a r a c t e r i s t i c s are  e  66 i n f u l l agreement with those previously reported f o r isogermacrone. Photolysis of Isogermacrone  (69).  A solution of 69_ (0.454 g,  0.00208 mole) i n 500 ml of benzene was photolysed i n t e r n a l l y through a Pyrex f i l t e r  for 55 min.  T i c (10% ether-benzene) indicated the  disappearance of s t a r t i n g material.  Removal of the benzene i n vacuo  gave a quantitative recovery of yellow o i l .  Vpc column P - l (200°,  60 ml/min) showed that the crude photolysis mixture contained seven products (A - G).  Their retention times were as follows (compd, ret  time, r e l amount): 4.86;  A, 2.9 min, 1.00; B_, 13.4 min, 9.07;  C_, 58.3 min,  D, 79.5 min, 96.8; E_, 86 min, 59.0; F, 96 min, 10.47; G,  min, 18.81.  122  Retention times were taken r e l a t i v e to the a i r peak.  The  major products at retention times 79.5 min (70, D) and 86 min (71, E) accounted f o r 78% of the t o t a l product mixture. crude mixture indicated the absence of v i n y l I s o l a t i o n of Photoproducts 70 and 71.  Nmr  (CDCl^) of this  hydrogens. The above photomixture  was subjected to preparative vpc column P - l (200°, 60 ml/min). Photoproducts 70_ and 71 were c o l l e c t e d i n this manner and found to be colorless liquids. Photoproduct 70 exhibited the following s p e c t r a l c h a r a c t e r i s t i c s : ir  (CHC1 ) 5.88 3  m, 4), 7.78 8.81 m/e  (C=0), and 6.14  (broad t , 3), 8.17  (s, 3, C -CH ), and 8.92 7  3  (C=C) y; nmr  (CDC1 ) T 7.25-7.61 (broad 3  (broad s, 3), 7.92-9.0 (broad m,  6)  (s, 3, C^-CH^); mass spectrum (70 eV)  ( r e l i n t e n s i t y ) 218(63), 207(37), 123(37), 122(50), 96(67), 91(37),  81(100), 79(57), 77(40), 68(63), and 67(47).  - 96 -  Anal. Calcd f o r C^H^O:  C, 82,51; H, 10.16.  Found:  C, 82.39;  H, 10.21. Photoproduct 7_1 had the following s p e c t r a l properties:  i r (CHCl^)  5.88 (C=0), and 6.13 (C=C) y; nmr CCDC1 ) x 7.18-7.97 (broad m, 6 ) , 3  7.97-9.0 (broad m, 7), 8.12 (broad s, 3), 9.10 (s, 3, C -CH ), 9.17 ?  3  (s, 3, C^-CR" ) ; mass spectrum (70 eV) m/e ( r e l i n t e n s i t y ) 218(12), 3  123(21), 122(52), 96(99), 95(80), 91(20), 81(100), 79(24), 77(20), 68(14), and 67(17). Anal. Calcd f o r C^H^O:  C, 82.51; H, 10.16.  Found:  C, 82.31;  H, 9.98. I s o l a t i o n of Photoproducts F and G.  Although present i n small  amounts, s u f f i c i e n t quantities of F_ and G_ needed f o r crude s p e c t r a l analyses were obtained by preparative vpc (column P - l , 200°, 60 ml/min) separation of an isogermacrone photolysis mixture. Photoproduct 1? c o l l e c t e d i n this manner gave the following spectral characteristics:  i r (CHC1 ) 5.95 (C=0), and 6.16 (C=C) y; 3  nmr (CDC1 ) x 7.00-9.30 (featureless broad multiplet with large 3  multiplet centres at x 7.80(1), 8.25(3) and 8.90(2). Photoproduct (2 c o l l e c t e d under i d e n t i c a l conditions showed the following spectral properties:  i r (CHC1 ) 5.90 (C=0), 6.13 (C=C) y; 3  nmr (CDC1 ) x 6.6-9.4 (broad multiplet with broad s i n g l e t s centred 3  at x 7.80(2), 8.17(2), 8.27(2), 9.13(1) and 9.25(1); mass spectrum (70 eV) m/e ( r e l i n t e n s i t y ) 218(100), 203(38), 175(27), 161(23), 147(32), 121(44), 119(32), 105(32), 96(47), 93(51), 91(66), 79(64), 77(44), 68(67), and 67(53).  - 97 -  Hydrogenation of Photoproduct 70 and 71. A solution of 7_0 (.200  g,  0.00092 mole) i n 15 ml ethyl acetate was hydrogenated over 8 mg of Adams Catalyst for 5 hrs. solvent  i n vacuo afforded  F i l t r a t i o n through C e l i t e and removal of 0.154  g of clear o i l .  Vpc column A-4  60 ml/min) indicated that the product was 90% pure. p u r i f i e d by c o l l e c t i o n on the same column. following spectral c h a r a c t e r i s t i c s :  This was  further  Hydrogenated 13  i r (CHCl^) 5.82  (165°,  gave the  (C=0) y; nmr  (CDC1 ) T 7.3-8.65 (featureless broad m, 10), 8.65-9.3 (featureless 3  m u l t i p l e t , 14); mass spectrum (70 eV) m/e  ( r e l i n t e n s i t y ) 220(26),  178(25), 121(54), 122(32), 109(50), 107(39), 96(84), 95(61), 93(44), 81(100), 79(36), and 68(27). Anal.Calcd f o r C^H^O:  C, 81.73; H, 11.00.  Found:  C, 81.36;  H, 11.18. In an analogous manner 71_ (50 mg, to give 40 mg of crude product.  0.227 mmoles) was  hydrogenated  Vpc column A-1 indicated that at  least 80% of the mixture was one product.  The following  c h a r a c t e r i s t i c s were taken on this crude mixture:  spectral  i r (CHCl^)  (C=0) y; mass spectrum ( p u r i f i e d by vpc c o l l e c t i o n ) (70 eV)  5.82  m/e  ( r e l i n t e n s i t y ) 220(7), 178(22), 136(19), 121(26), 109(21), 107(24), 96(90), 95(37), 93(27), 81(100), 79(29), and 68(25). Synthesis of syn (73) and a n t i (74) 1,7-Dimethyltricyclo decane97 3-one.  A s o l u t i o n of 1,2-dimethyl cyclopentene (Chemical Samples,  99% pure) (22.43 g, 0.233 mole) i n absolute ether (175 ml) was photolysed through Corex f o r 8 hours. Chemical Co.)  Cyclopentenone (Aldrich  (13.00 g, 0.158 mole) was added dropwise to t h i s  solution at various times throughout the photolysis.  The  photolysis  - 98 -  was followed by vpc column A-1  (150°, 60 ml/min).  The ether and the  majority of the s t a r t i n g materials were removed i n vacuo to give 15.92 g of a yellow-orange l i q u i d .  According to column A-1, 57%  of the crude product mixture was _73 and 74 i n a 5:3 r a t i o respectively. The two desired products were i s o l a t e d and p u r i f i e d by preparative vpc  column P-3  (210°, 60 ml/min).  The following s p e c t r a l properties were obtained f o r 73_: 5.83  (C=0) ; nmr  (CDC1 ) x 6.33  u  3  11, C , C , Cg, C , C 4  8.93  5  g  CH  1 0  2  (s, 1, C  and C  CH),  g  i r (CHCl^)  CH), 7.30-9.00 (broad m,  2  8.85  (s, 3, C ~ C H ) , and  (s, 3, C^^-CH ); mass spectrum (70 eV) m/e 3  12  3  ( r e l intensity)  178(24), 121(30), 109(26), 107(30), 96(65), 95(36), 93(38), 91(37), 81(100), and 79(40). Anal. Calcd f o r C^H^O:  C, 80.81; H, 10.12.  Found:  C, 80.84;  H, 10.25. Photoproduct _7_4 exhibited the following s p e c t r a l properties: ir  (CHC1 ) 5.83 3  (m, 5, C , C 4  8.99 m/e  5  CH  (C=0) y; nmr 2  and C  &  (CDC1 ) x 6.38  (s, 1, C  2  CH), 7.45-8.05  CH), 8.05-8.80 (m, 6, C , C  g  and C  g  (s, 3, C - C H ) , and 9.11 12  3  3  1 Q  CH ), 2  (s, 3, C^-CH^ ; mass spectrum (70 eV)  ( r e l i n t e n s i t y ) 178(24), 136(20), 121(20), 107(18), 96(72), 95(27),  93(20), 81(100), and 79(24). Anal. Calcd for C H 0 : 1 0  H,  1 0  C, 80.81; H, 10.12.  Found:  C, 80.59;  9.99. 2 6 Condensation of syn-1,7-Dimethyltricyco[5.3.0.0 ' ]decane-3-one 72  (73) with Acetone.  A solution of 73_ (0.088 g, 0.00049 mole),  acetone (0.440 g, 0.0076 mole), and sodium metal (0.0644 g, 0.0028 mole) i n absolute ethanol (15 ml) was refluxed under nitrogen with s t i r r i n g  - 99 -  for four hrs.  A f t e r t h i s p e r i o d , t i c (10% e t h e r - b e n z e n e )  the d i s a p p e a r a n c e of s t a r t i n g m a t e r i a l and the f o r m a t i o n product. acid.  indicated of a s i n g l e  The s o l u t i o n was n e u t r a l i z e d w i t h d i l u t e aqueous h y d r o c h l o r i c  The e t h a n o l was  removed i n vacuo and t h e r e s i d u e was  i n 10 ml of e t h e r and 10 m l of w a t e r .  t a k e n up  The l a y e r s were s e p a r a t e d and  the aqueous l a y e r was e x t r a c t e d w i t h e t h e r  (1 x 10 m l ) .  The  ether  e x t r a c t s were combined, washed w i t h w a t e r (1 x 10 m l ) , and d r i e d (Na2S0^). oil.  The e t h e r was removed i n vacuo t o y i e l d 0.095 g o f  Vpc column A-3  was  compound 70.  was  identical  of  (170°, 40 ml/min) i n d i c a t e d t h a t 95% o f t h i s o i l  P u r i f i c a t i o n by vpc (column A-3)  a f f o r d e d _7_P_ w h i c h  (nmr, i r , mass spectrum) t o 7_0 o b t a i n e d  i n the p h o t o l y s i s  isogermacrone. C o n d e n s a t i o n of a n t i - l , 7 - D i m e t h y l t r i c y c l o [ 5 . 3 . 0 . 0  (74) w i t h A c e t o n e . was  yellow  2 6 72 ' ]decane-3-one  I n a s i m i l a r manner 74_ (0.131 g, 0.00074 mole)  condensed w i t h acetone (1.4 g, 0.0242 mole) i n an e t h a n o l i c  s o l u t i o n (15 ml) c o n t a i n i n g sodium m e t a l (0.0856 g, 0.00372 m o l e ) . Workup i n the u s u a l manner y i e l d e d 0.170 column A-3 71.  g of y e l l o w o i l .  Vpc  (170°, 40 ml/min) i n d i c a t e d t h a t 88% o f t h e o i l was  compound  P u r i f i c a t i o n by vpc y i e l d e d pure 71^ w h i c h was i n d i s t i n g u i s h a b l e  (nmr, i r , mass spectrum) from 71_ i s o l a t e d i n the " p h o t o l y s i s o f isogermacrone.  C)  ACYCLIC DIENE-DIESTER 74 Preparation  of D i e t h y l t r a n s , t r a n s - d e c a - 2 , 8 - d i e n e - l , 1 0 - d i o a t e .  75 *  A m i x t u r e o f 1 , 1 0 - d e c a n e d i o i c a c i d (Eastman O r g a n i c C h e m i c a l s , t e c h n i c a l grade)  (120 g, 0.59  mole) and t h i o n y l c h l o r i d e (BDH)  (171 g, 1.43  mole) i n  a flame d r i e d t h r e e - n e c k e d 1 l i t r e round bottom f l a s k f i t t e d w i t h a  - 100 -  condenser and drying tube was refluxed at 90° f o r 2 hrs.  Heating was  discontinued, and bromine (AnalaR) (229 g, 1.43 mole) was added 74 dropwise to the clear yellow s o l u t i o n .  During the addition the  complete apparatus was i r r a d i a t e d with a 275W sun lamp.  After the  addition was complete (1 h r ) , the dark brown s o l u t i o n was heated i n the dark between 90 and 100° f o r 5 hrs.  The solution was then cooled  to 0° and absolute ethanol (165 ml) was added dropwise followed by a s o l u t i o n of sodium bicarbonate (25.84 g water.  Chloroform  separated.  0.308 mole) i n 205 ml of  }  (200 ml) was added and the two layers were  The aqueous layer was extracted with chloroform (2 x 100 ml).  The combined chloroform extracts were washed with saturated sodium bicarbonate solution (2 x 200 ml), water (2 x 200 ml) and saturated sodium bicarbonate s o l u t i o n (2 x 200 ml), decolorized (Norit), and dried (MgSO^).  The chloroform was removed i n vacuo to y i e l d 210 g  of a l i g h t yellow l i q u i d .  The following s p e c t r a l data confirmed  l i q u i d to be diethyl-2,8-dibromodecane-l,10-dioate:  i r (neat) 5.78  (C=0) u; nmr (CC1 ) x 5.78 (q, 4, C00CH_ CH ) , 4.00 ( t , 2, J 4  2  this  3  2 3  = 7.2 Hz,  CHBr-COOEt), 8.00 (m, 4, CH CHBr-C00Et), and 8.70 (m, 8, C., C , C,, o  —  c  —Z  and Cj CH ). 2  H  J  O  The crude yellow o i l (210 g, 0.504 mole) was refluxed  i n dimethyl formamide (420 ml) f o r 4 h r s .  7 5  The s o l u t i o n was cooled  and to i t were added 800 ml of water and 300 ml of ether. was then separated.  The mixture  The aqueous layer was extracted with ether  (2 x 100 ml) and the ether extracts were combined.  These were washed  with water (2 x 200 ml) and saturated sodium chloride solution (2 x 200 ml), decolorized (Norit), and dried (MgSO^).  The ether was  removed i n vacuo to give 124 g (97%) of an orange l i q u i d .  Vpc column  - 101 -  A-2 (170°, 120 ml/min) indicated that 60% of the crude product mixture was 79 and that 20% of i t was the c i s , trans isomer J50.  Distillation  through a Vigreux column resulted i n a c o l o r l e s s l i q u i d , bp 104° at 0.02 mm  (reported "* bp 127° at 0.28 mm). 7  Further d i s t i l l a t i o n s were  necessary to completely separate 7_9_ from the product mixture.  Compound  79 prepared i n this manner showed the following s p e c t r a l data:  uv max  (hexane) 207 nm (e 23,000), and sh 241 nm (E 410); i r (neat) 5.81 (C=0), 6.06, and 10.15 y; nmr (CCl^) T 3.06 (d of t , > 2  15.5 Hz, J_ . = J , J  0  J 2  3  =  J  8 9  =  = 6.8 Hz, trans CH=CH-C00Et) , 4.22 (d, 2, J„  =  _ = 15.5 Hz, trans CH=CH-C00Et), 5.85 (q, 4, C00CH_CH_), 7.78 o, y — —z j Q  (broad d, 4, J_ . = J.,  Q  C  6  = 6.8 Hz, C. and C, CH ) , 8.50 (m, 4, C,. and 0  CH ), and 8.73 ( t , 6, C00CH CH ); mass spectrum 2  2  3  (70 eV) m/e ( r e l  i n t e n s i t y ) 254(9), 209(24), 208(23), 182(28), 181(70), 163(57), 16237), 152(14), 140(24), 135(97), 134(75), 108C26), 107(100), 106(45), 93(30), 89(29), 81(66), 79(51), 68(47), and 67(58). Direct Photolysis of Diethyl trans,trans-deca-2,8-diene-l,10dioate (79).  This photolysis could be carried out i n either methanol  or hexane with no observed differences; the following description i s typical.  Diene-diester 79_ (2.54 g, 10 mmole) i n 1 1. of methanol was  i r r a d i a t e d through Vycor and the course of the reaction followed by a n a l y t i c a l vapour phase chromatography 120 ml/min).  using column A-2 (170°,  Five new peaks i n addition to s t a r t i n g material were  observed corresponding to photoproducts 80, 81, 115, 116 and 117 the 98 l a t t e r being the ultimate sole product a f t e r 2.5 hrs of i r r a d i a t i o n . The retention times were as follows (ret time, compound):  10.5 min,  81; 11.7 min, 116; 12.9 min, 117; 16.2 min, 80; 17.5 min, 115; and 28.2 min, 79.  - 102 -  I s o l a t i o n and I d e n t i f i c a t i o n of Photoproducts 80, 81, 115, 116, and 117.  I r r a d i a t i o n as above f o r 90 min led to near-maximum amounts  of photoproducts 80_, 8^, 115 and 116.  These products were separated  and i s o l a t e d by vpc column P-2 ( 1 7 5 ° , 200 ml/min).  Photoisomer 117,  was i s o l a t e d by preparative vpc column P - l ( 2 0 0 ° , 60 ml/min) of the f i n a l (2.5 hr) photolysis mixture.  A l l the products were c o l o r l e s s  liquids. The structure of 80_ was deduced to be d i e t h y l diene-1,10-dioate  from the following data:  cis,trans^-deca-2,8-  uv max (isooctane) 208 nm  (e 22,000), and sh 241 nm (e 425); i r (neat) 5.81 (C=0), 6.07, 10.04, and 11.97 y; nmr (CC1.) x 3.20 (d of t , 1, J  _ » 15.5 Hz, J ,  0  o, y  H  6.8 Hz, trans CH=CH-C00Et), 3.92 (d of t , 1, J 7.3 Hz, c i s CH=CH-C00Et), 4.32 Cd, 1, J 4.36 (d, 1, J  2  3  g  g  0  =  /,o = 11.5 Hz, J_ , =  = 15.5 Hz, trans CH=CH-C00Et),  = 11.5 Hz, c i s CH=CH-C00Et), 5.94 (q, 4, COOCH^CH^,  7.37 (broad d, 2, J_ . = 7.3 Hz, C. CH„), 7.80 (broad d, 2,  „ = 6.8  Hz, C CH ) , 8.52 (m, 4, C and C CH ) , and 8.76 ( t , 6, COOCH CH_ ); ?  2  5  mass spectrum parent  g  2  (70 eV) m/e 254.  2  3  Photoproduct 1_ was i d e n t i c a l  to an independently prepared sample of d i e t h y l diene-1,10-dioate. Photoisomer J31_ was shown to be d i e t h y l  cis,trans-deca-2,8-  75  1,10-dioate from the following:  cis,cis-deca-2,8-diene-  i r (neat) 5.82 (C=0), 6.07, and 12.04 y ;  nmr (CC1.) x3.91 (d of t, 2, J_ „ = J . = 11.6 Hz, J . . = J , - = 7.3 Hz, ^ Z,J o,y J,4 /,o n  c i s CH=CH-C00Et), 4.38 (d, 2, J  = J z, J  o, y  = 11.6 Hz, c i s CH=CH-C00Et),  5.95 (q, 4, C00CH C H . ) , 7.37 (broad d, 4, J . . = C  ?  0  = 7.3 Hz, C. and  C H ) , 8.53 (m, 4, C and C CH ) , and 8.78 (t, 6, C00CH CH_ ) ; mass 2  5  &  2  2  3  spectrum (70 eV) m/e ( r e l i n t e n s i t y ) 254(2), 209(10), 181(14), 173(16), 149(36), 135(19),,107(15), 95(17), 91(30), 81(100), and 67(21).  - 103 -  Anal. Calcd f o r 4 C  H  1  2  2°4  :  C  »  66  ' '* 12  H  '  8 , 7 2 #  F  o  u  n  d  :  c  » 65.94;  H, 8.59. Photoisomer 115 was shown to have the structure d i e t h y l trans,transdeca-3,8-diene-l,10-dioate from the following data:  i r (neat) 5.79  (C=0), 5.82 (C=0), 6.07, and 10.18 y; nmr (CC1 ) x 3.18 (d of t , 1, 4  J  o,y Q  n  = 15.4 Hz, J., _ = 6.8 Hz, trans CH=CH-C00Et), 4.32 (d, 1, J _ = /,o — o,y Q  15.4 Hz, trans CH=CH-C00Et), 4.50 (m, 2, CH=CH), 5.90 (q, 2, COOCH^CH^, 5.92 (q, 2, C00CH CH ), 7.07 (m, 2, C 2  8.38 (m, 2, C  g  3  2  CH ) , 7.85 (m, 4, C 2  5  and C CH ), y  2  CH ), and 8.70 ( t , 6, C00CH CH_ ) ; mass spectrum (70 eV) 2  2  3  m/e ( r e l i n t e n s i t y ) 254(2.5), 2090-5), 208(14), 179(18), 163(19), 162(22), 140(34), 135(58), 134(50), 114(58), 107(62), 99(30), 93(43), 86(45), 81(79), 79(41), 68(76), and 67(100). Anal. Calcd f o r C..H ,,0. : 14 22 4  C, 66.12; H, 8.72. Found:  o  C, 65.94;  H, 8.80. Photoproduct 116 was proved to be d i e t h y l deca-trans-3-cis-8diene-1,10-dioate from the following:  i r (neat) 5.79 (C=0), 5.83  (C=0), 6.12, 10.14, and 11.93 y; nmr (CCl^) x 3.91 (d of t , 1, J 11.5 Hz, J  ?g  = 7.2 Hz, c i s CH=CH-C00Et), 4.37 (d, 1, J  gg  =  = 11.5 Hz,  gg  c i s CH=CH-C00Et) , 4.53 (m, 2, CH=CH) , 5.95 (q, 2, COOCH^CH^ , 5.97 (q, 2, C00CH„CH_), 7.09 (m, 2, C„ CH_) , 7.38 (broad d, 2, J-, = 7.2 Hz, Q  J  —Z  C-, CH„), 7.93 (m, 2, C /  Z  I,O  L i . c  _>  CH.) , 8.43 (m, 2, Z, CH ) , 8.75 and 8.78 ( t , 6, 0  Z  D  z  C00CH CH_ ) ; mass spectrum parent (70 eV) m/e 254. 2  3  Anal.Calcd for C^H^O^:  C, 66.12; H, 8.72. Found:  C, 66.14;  H, 8.55. Compound 117 was i d e n t i f i e d as d i e t h y l trans,trans-deca-3,7-dieneI, 10-dioate on the basis of the following information:  uv max (hexane)  - 104 -  208 nm (e 1300); i r (neat) 5.74 (C=0), and 10.27 y; nmr (CCl^) T 4.45 (m, 4, CH=CH), 5.87 (q, 4, COOCH_ CH ) , 6.97 (m, 4, C 2  7.87 (broad s, 4, C  and C  5  3  and C  2  CH ) ,  g  2  CH ) , and 8.73 ( t , 6, COOC^CH^) , mass  &  2  spectrum (70 eV) m/e ( r e l i n t e n s i t y ) 2 5 4 ( 2 1 ) , 209(57), 208(50), 181(69), 179(50), 162(35), 135(91), 134(53), 127(67), 108(59), 107(78), 99(53), 93(78), 91(60), 85(72), 81(83), 7 9 ( 1 0 0 ) , and 67(86). The nmr (HA-100) of a CCl^ solution containing 70 mg of 117 plus 93 30 mg of Eu(DPM)  showed the following signals a t t r i b u t a b l e to the  3  v i n y l hydrogens at C 2 3 8 9 ' J  =  J  =  6  ,  8 H z  t  r  a  3 n  and C : T 3.30 (d of t , 2, J ^ = J = 15.7 Hz, CH=CH-CH -C00Et). The and vinyls g  s  3  appeared as: T 3.68 (broad d, 2, J „ . = 3,h  CH=CH-CH -C00Et).  I r r a d i a t i o n at C  2  7g  2  2  and C  = 15.7 Hz, trans  0  /,» g  caused the C  hydrogens to appear as a doublet, J = 15.5 Hz.  and C  3  g  vinyl  I r r a d i a t i o n at C,. and  Cg caused sharpening of the C^ and C^ doublet. A 60% aqueous dioxane s o l u t i o n of 117 (150 mg) containing 0.3 ml of cone HCl was refluxed under nitrogen f o r 22 hrs.  Removal of the  solvent i n vacuo afforded a wet white s o l i d residue which was r e c r y s t a l l i z e d from water, f i l t e r e d , and dried over R ^5 i  vacuo to  n  2  y i e l d 35 mg of yellow c r y s t a l s .  Norit d e c o l o r i z a t i o n followed by a  further r e c r y s t a l l i z a t i o n from water afforded 25 mg of pure trans,transdeca-3,7-diene-l,10-dioic acid, mp 1 1 8 ° - 1 2 0 ° ( l i t . ir  9 5  118°-120°).  (KBr) 3.56 (OH), 5.91 (C=0), and 10.37 y; nmr (DMSO d ) &  (m, 4, CH=CH), 7.03 (m, 4, C CH2)•  2  and C CT^), and 7.90 (s, 4, C g  4.47  T  5  and Cg  This material was i d e n t i c a l (mixed mp, i r , and nmr) to an  authentic  sample.  95  - 105 -  Anal. Calcd f o r C^H^O^:  C, 60.59;  H, 7.12.  Found:  C, 60.63;  H, 7.21. Direct Photolysis of Diethyl cis,trans-deca-2,8-diene-l,10dioate (80).  Compound J50 (211 mg) i n 200 ml of hexane was i r r a d i a t e d  through a Vycor f i l t e r and the course of the reaction followed by vpc column A-2 (160°, 180 ml/min).  Peaks a t t r i b u t a b l e to photoproducts  81, 115, and 116 grew and then diminished while s t e a d i l y decreased  the peak due to j$0  and that due to 117 steadily increased.  After  98 30 min, 117 was the only product detectable by vpc. corresponding  to _79_ was not observed  A peak  at any time during the photolysis.  A preparative vpc-collected (column P - l , 200°, 60 ml/min) sample of 117 from this run was i d e n t i c a l to previous samples. Direct Photolysis of D i e t h y l dioate (115).  trans,trans-deca-3,8-diene-l,10-  Compound 115 (62 mg) i n 45 ml of hexane was  photolysed  externally through Corex and the reaction followed by vpc column A-2 (159°, 150 ml/min).  For the f i r s t hour the disappearance  the appearance of 116 was observed.  of 115 and  At this point a peak  corresponding  to 117 appeared, u n t i l a f t e r 2.15 hrs there were  approximately  equal amounts of 115, 116 and 117.  was the sole product  (> 95%) detectable by vpc.  photolysis were peaks corresponding  After 3.6 hrs, 117 At no point during the  to isomers 79, 80 or  observed.  A sample of 117 from t h i s run, collected by preparative vpc (column P-l,  200°, 60 ml/min) was i d e n t i c a l to previous samples. Acetone-Sensitized Photolysis of Diethyl  diene-1,10-dioate  trans,trans-deca-2,8-  (79). Diene-diester 79 (1.27 g, 5 mmole) i n 400 ml of  acetone was i r r a d i a t e d through Corex (X > 260 nm) and the course of the  - 106 -  reaction followed by a n a l y t i c a l vpc using column A-2  (170°, 120 ml/min).  The percentage of the incident i r r a d i a t i o n absorbed by the acetone at various wavelengths was absorbed by s e n s i t i z e r = C  calculated using the r e l a t i o n : c  e /C c  Q  E„ + C  e  % light  i n which S refers to the  s e n s i t i z e r (acetone), D i s the substrate being s e n s i t i z e d  (diene-diester),  C i s the molar concentration, and e i s the e x t i n c t i o n c o e f f i c i e n t at the wavelength  i n question.  (wavelength, %) :  255 nm,  The calculated percentages are as follows 97.7%; 260 nm,  98.7%;  265 nm,  99.2%.  After  40 min a photostationary state mixture of products 79_, 80, and 81_ (94%) was  formed i n the r a t i o of 3.8 : 3.5 : 1.0.  by column P-2  These products were i s o l a t e d  (170°, 200 ml/min) and i d e n t i f i e d by i r , nmr,  and vpc  retention time. In a separate experiment, 0.51'g acetone was  (2 mmole) of 79^ i n 500 ml of  i r r a d i a t e d through Corex u n t i l vpc column A-2  indicated  the presence of products 82_ - 85_ and the disappearance of geometric isomers 79^ - J50 (8.5 h r s ) .  The 79 : 80 : 81^ r a t i o remained  constant at  3.8 : 3.5 : 1.0 during the transformation into c y c l i z e d products 82_ - 85. Compounds J32_ - J55_ had the following retention times on column A-2 200 ml/min):  (150°,  11.8 min, 82; 15.1 min, 83; 16.2 min, 85; and 19.7 min, 84.  The products were formed i n the following r e l a t i v e amounts (average of three runs):  82 (42%), 83 (15%), 84 (36%), and 85_ ( 7 % ) ; further  i r r a d i a t i o n l e d to loss of y i e l d and eventual loss of any i s o l a b l e products. I s o l a t i o n and I d e n t i f i c a t i o n of Cyclized Products 82 - 85. crude photolysate from above (525 mg) was on column P-2  The  subjected to preparative vpc  (165°, 200 ml/min) and the i s o l a t e d products 82_ - 85_ further  p u r i f i e d by Kugelrohr d i s t i l l a t i o n ; a l l were c o l o r l e s s l i q u i d s .  On  - 107 -  larger scale photolyses the crude photolysate was i n i t i a l l y p u r i f i e d by e l u t i o n on s i l i c a g e l with 10% ether-benzene.  This e f f e c t i v e l y  removed any acetone by-products and any polymers which may have formed. The p u r i f i e d photolysate was then subjected to vpc separation as described above. Photoproduct 82 had the following s p e c t r a l c h a r a c t e r i s t i c s : i r (neat) 5.97 (C=0) ; nmr (CC1 ) u  J = 9.5 Hz, 2,  4  x  5.88  (q, 4, COOCH^CR^), 6.80 (d,  CH-COOEt), 7.57 (m, 2, CH-CH-COOEt), 8.43 (m, 8,  cyclohexane ring CH^), and 8.70 ( t , 6, COOCH^CH^); mass spectrum (70 eV) m/e_ ( r e l intensity) 255(.67), 254(.80), 225(1.1), 210(2.5) , 209(17), 208(4.2), 182(13), 181(100), 180(4.6), 173(4.1), 153(5.1), 145(3.5), 136(5.9), 135(45), 134(4.8), 127(9.5), 117(5.2), 105(4.5), 107(19), 99(7.9), 93(6.3), 91(6.0), 81(8.7), 79(17), 77(5.7), and 67(14). Photoproduct 83 exhibited the following spectral data:  i r (neat)  5.79 (C=0) y; nmr (CCl^) x 5.88 (q, 4, COOCH^CK^, 6.80 (d, J = 9.5 Hz, 2, CH-COOEt), 7.57 (m, 2, CH-CH-COOEt), 8.43 (m, 8, cyclohexane ring CH ) , and 8.70 ( t , 6, COOCH CH_ ) ; mass spectrum (70 eV) m/e ( r e l 2  2  3  intensity) 254(6), 209(20), 208(9.5), 181(31), 182(11), 173(54), 149(30), 145(21), 135(35), 134(11), 127(34), 117(15), 107(25), 99(19), 96(16), 93(14), 91(20), 81(100), 79(30), 77(20), and 67(29). Photoisomer 8_4_ had the following spectral c h a r a c t e r i s t i c s : i r (neat) 5.78 (C=0) y; nmr (CC1 ) x 5.95 (q, 4, COOCH CH ), 7.05 (m, 2, 4  2  3  CH-COOEt), 7.34 (m, 2, CH-CH-COOEt), 8.52 (m, 8, cyclohexane r i n g CH ), 2  and 8.80 ( t , 6, COOCH CH_ ) ; mass spectrum (70 eV) m/e ( r e l i n t e n s i t y ) 2  3  255(2.3), 254(2.6), 209(45), 208(31), 182(14), 181(100), 180(15),  - 108 -  173(9), 153(13), 136(9), 135(72), 134(13), 127(23), 117(13), 107(31), 105(12), 99(35), 93(15), 81(20), 79(49), 77(18), and 67(40). Photoproduct 85_ could not be obtained free of isomer j5_3 due to t h e i r s i m i l a r vpc retention times.  Spectra of 85_ s l i g h t l y contaminated  with 8^3 were i n accord with the structure proposed: u ; nmr (CC± ) 4  T  i r (neat) 5.80 (C=0)  5.90 (q, 2, COOCH^CH^), 5.93 (q, 2, C00CH_ CH ), 6.402  3  9.00 (m, 12, CH-CH-(CH ) -CH-CH) , 8.72 and 8.73 ( t , 6, C00CH CH_ ) ; 2  4  2  3  mass spectrum (70 eV) m/e ( r e l i n t e n s i t y ) 254(1.6), 225(1.1), 210(6.1), 209(38), 208(10), 182(13), 181(100), 180(7.4), 173(6.8), 153(5.8), 136(6.3), 135(50), 134(5.8), 127(15), 117(4.5), 107(15), 99(12), 93(7.1), 91(5.8), 81(12), 79(13), and 67(14).  The structure of 85 was  proved by sodium ethoxide-catalyzed epimerization (vide i n f r a ) to the more stable trans-fused isomer 82_ i n d i r e c t analogy to r e s u l t s obtained 78 with the corresponding dimethyl esters. The structures of photoproducts J32_ -  were proved by d i r e c t compar-  ison (retention time, i r , and nmr) with authentic samples obtained by the photoaddition of d i e t h y l maleate to cyclohexene.  77  A solution of  d i e t h y l maleate (26.6 g, 0.155 mole) i n cyclohexene (200 ml, 162 g, 1.98 mole) was i r r a d i a t e d through Vycor f o r 9 hrs.  Removal of the  cyclohexene i n vacuo afforded 32.5 g of crude product mixture.  This  yellow o i l was d i s t i l l e d (0.05 mm) and then subjected to preparative vpc column P-2 (163°, 120 ml/min).  Four peaks corresponding i n  retention times to J32_ - 85_ were c o l l e c t e d .  Three of these proved to  be i d e n t i c a l (retention times, i r , and nmr) to J32_, 8_3, and J34.  The  remaining compound corresponding i n retention time to 85_ was found to be unsaturated.  - 109 -  Further evidence for the structures of j52_, 83_ and 8h_ came from t h e i r hydrolyses  to the known dicarboxylic acids.  In general one mmole of  diester was refluxed i n 5 ml of aqueous 2 N NaOH under nitrogen for 2 hrs.  The s o l u t i o n was a c i d i f i e d  centrifuged.  (aqueous HC1) to litmus, cooled, and  The white s o l i d was washed twice with cold water.  trans,anti,trans-Bicyclo[4.2.0]octane-7,8-dicarboxylic  acid  obtained from the hydrolysis of 82_ was r e c r y s t a l l i z e d once from ethyl acetate-petroleum  ether to give the pure d i a c i d , mp 180°-182°  (lit.  7 7  181°-182°); nmr (DMSO-dg) x 7.17 (m, 2, CH-C00H), 8.53 (m, 10, -CH-(CH ) -CH). 2  4  S i m i l a r l y j$3 afforded, a f t e r two r e c r y s t a l l i z a t i o n s from 20% acetonebenzene, pure cis,trans-bicyclo[4.2.0]octane-7,8-dicarboxylic a c i d , mp 197°-198° ( l i t .  7 7  mp 199°-200°); nmr (acetone d ) x 6.70 (d, 2, g  CHCOOH), 7.47 (m, 2, CH-CH-COOH), and 8.43 (m, 8, cyclohexane ring CH ). 2  Hydrolysis of 84_ gave cis,anti,cis-bicyclo[4.2.0]octane-7,8dicarboxylic acid.  Three r e c r y s t a l l i z a t i o n s from e t h y l  ether gave a mp of 170°-172° ( l i t .  7 7  acetate-petroleum  174°-176°); nmr (acetone d ) x 6.87 fi  (m, 2, CH-COOH), 7.30 (m, 2, CH-CH-COOH), and 8.43 (m, 8, cyclohexane ring CH ). 2  Acetone-Sensitized 1,10-dioate (80).  Photolysis of Diethyl-cis,trans-deca-2,8-diene-  Diene-diester 80 (0.16 g, 0.63 mmole) i n 200 ml of  acetone was i r r a d i a t e d through Corex to give an i n i t i a l 3.8 : 3.5 : 1.0 mixture of products 7_9_, 80_, and 81_ respectively.  Further photolysis  (2.8 hrs) caused the disappearance of geometric isomers 7_9_ - j?l with the concommitant formation r e l a t i v e amounts:  of c y c l i z e d products 82_ - 85_ i n the following  82 (44%), 83 (18%), 84 (31%), and 85 (7%).  These  - 110 -  photoproducts were i d e n t i c a l i n vpc retention times and s p e c t r a l c h a r a c t e r i s t i c s to those previously observed. Acetone-Sensitized 1,10-dioate (81).  Photolysis of Diethyl-cis,cis-deca-2,8-diene-  Diene-diester  81 (89 mg, 0.35 mmole) i n 50 ml of  acetone was i r r a d i a t e d externally through Corex u n t i l only photoproducts 82 - 85_ were present (5.5 h r s ) . of yellow o i l .  Removal of the acetone y i e l d e d 0.144 g  The products were separated by preparative vpc column  P-2 (170°, 150 ml/min) and were i d e n t i c a l i n a l l respects to those obtained i n the photolysis of 7_9_ and J50.  The i n i t i a l l y formed geometric  isomers never reached an equilibrium state as i n the photolysis of 79_ and  80_, and the f i n a l 82_ - j35_ photostationary  follows:  state mixture d i f f e r e d as  82 (26%), 83 (17%), 84 (49%), and 85 ( 8 % ) .  Acetophenone-Sensitized Photolysis of 79.  trans,trans-Diene-diester  79 (0.254 g, 1 mmole) and acetophenone (0.240 g, 2 mmole) i n 200 ml of benzene were i r r a d i a t e d through Pyrex and the reaction c a r e f u l l y by column A-2 (168°, 200 ml/min).  followed  I n i t i a l l y the r a t i o s of  79, 80, and j31_ were i d e n t i c a l to those found i n the acetone-sensitized photolysis of ]9_ and 80.  A f t e r 24 hrs, only products 82_ - j$5_ remained  i n the following r e l a t i v e amounts (obtained ml/min):  from column P-2, 170°, 180  82 (45%), 83 (16%), 84 (31%), and 85 ( 8 % ) .  The photoproducts  were i d e n t i f i e d by t h e i r vpc retention times and i r spectra which were i d e n t i c a l to previously i s o l a t e d samples.  Benzophenone was also  found to s e n s i t i z e the cycloaddition, but because of i t s retention time, the r a t i o s of 82 - 85_ could not be obtained. to s e n s i t i z e the photocycloaddition.  Naphthalene f a i l e d  - Ill -  Base-Catalyzed Epimerization of Cyclized Products 82 - 85.  Diethyl  trans,anti,trans-bicyclo[4.2.0]octane-7,8-dicarboxylate (82) (0.052 g, 0.21 mmole) and sodium (5 mg)  i n 1.5 ml of abs ethanol were sealed i n  a v i a l and heated for 12 hrs at 80°.  The ethanol was  water added, and the mixture a c i d i f i e d (aqueous HC1) aqueous layer was extracted with chloroform ( 5 x 2 chloroform extracts were washed with water ( 1 x 4 The chloroform was vpc column A-2  removed i n vacuo, to litmus.  ml).  The  The combined  ml) and dried (MgSO^).  removed i n vacuo to y i e l d 0.036 g of o i l .  Analytical  (168°, 200 ml/min) indicated the presence of three  products i n the r a t i o 87 : 10 : 3.  The f i r s t of these was  s t a r t i n g material (vpc, i r , nmr), and the second was isomer 85_ by vpc retention time and i r .  i d e n t i c a l to  shown to be stereo-  The t h i r d product, present  i n minute q u a n t i t i e s , was not i s o l a t e d . c i s , a n t i , c i s - D i e s t e r 84 (0.068 g, 0.28 mmole) under i d e n t i c a l conditions gave 0.054 g of o i l . two products i n an 86 : 14 r a t i o .  Column A-2  (168°, 200 ml/min) showed  Spectral data and vpc retention times  proved the major product to be photoproduct 83_ and the minor product to be 84. A 50 : 50 mixture of isomers j8_3 and 85_ (0.047 g, 0.19 mmole) gave four products corresponding i n retention times to j}2_, 83_, 84, and J35_ after being subjected to the basic conditions previously described.  The r a t i o s of  82 : 85 and j$3 : 814 were 90 : 10 and 85 : 15 respectively.  Compounds 82  and 84_ prepared i n t h i s manner had i d e n t i c a l s p e c t r a l properties to those previously observed. Thermolysis of Diesters 82, 83, and 84.  Diester 84 (0.030 g,  0.11 mmole) was heated i n a sealed tube at 250° for 88 hrs.  Vpc column  - 112  A-2  (168°, 100 ml/min) i n d i c a t e d t h a t the d i e s t e r s l o w l y  to d i e s t e r 83. was  -  observed.  of b o t h was  thermolysed  A f t e r 28 h r s , no f u r t h e r change i n the j53_ : 8_4 r a t i o T h i s r a t i o c o n s i s t e d o f 81% 83 and 19% 84_; the i d e n t i t y  a u t h e n t i c a t e d by vpc and i r .  With the e x c e p t i o n of  two  low r e t e n t i o n time p r o d u c t s ( d i e t h y l m a l e a t e and c y c l o h e x e n e on the b a s i s of r e t e n t i o n t i m e s , sum  < 1 % ) , t h e s e were the o n l y two p r o d u c t s  observed. D i e s t e r 83_ (0.030 g, 0.11 mmole) under i d e n t i c a l c o n d i t i o n s gave a m i x t u r e of 83 (82%) and 84 (18%) a f t e r 62 h r s . D i e s t e r 8_2_ i n i t i a l l y appeared  t o g i v e the same p r o d u c t s as i n i t s  b a s e - c a t a l y z e d e p i m e r i z a t i o n , but upon i n c r e a s e d t h e r m o l y s i s times (88 h r s ) , 82_ was of 1.1  : 1.0  c o n v e r t e d t o a m i x t u r e of f i v e p r o d u c t s i n the r a t i o  : 3.3  : 1.6  : 1.2.  The r e m a i n i n g p r o d u c t s were not  D)  The f i r s t of t h e s e i s d i e s t e r  82.  identified.  CYCL0N0NA-2,6-DIENONE 99 S y n t h e s i s of 9,9-Dibromobicyclo[6.1.0]non-4-ene  (123).  Dry  t-BuOH (1 1.) was poured i n t o a f l a m e d r i e d 2 1. 3-necked f l a s k , f i t t e d w i t h an overhead m e c h a n i c a l s t i r r e r , a n i t r o g e n i n l e t , and a condenser equipped w i t h a d r y i n g tube. mole) was to  added w i t h s t i r r i n g t o t h e t-BuOH.  completely react l a s t traces of potassium.  s o l u t i o n was of  P o t a s s i u m m e t a l (50 g,  90°C.  1.28  R e f l u x i n g proved n e c e s s a r y The c l e a r p a l e y e l l o w  t h e n d i s t i l l e d to remove t h e t-BuOH a t a p o t  temperature  When the p o t a s s i u m t - b u t o x i d e came out o f s o l u t i o n , 200  of pentane were added and t h e n removed by d i s t i l l a t i o n . repeated s i x times.  mis  T h i s was  H e a t i n g was d i s c o n t i n u e d and an a d d i t i o n a l 300  mis  - 113 -  of pentane were added.  This white suspension of potassium t-butoxide  i n pentane was cooled i n a s a l t - i c e bath.  To this cooled suspension  was added cyclooctadiene (107 g, 1.0 moles). pentane  Then, with s t i r r i n g , a  (200 ml) solution of bromoform (253 g, 1.0 mole) was added  dropwise over a period of 5 hrs. night at room temperature.  The mixture was then s t i r r e d over-  I t was then poured into 800 mis of water •I  Q  and f i l t e r e d to give 63.5 g of 9,9,10,10-tetrabromotricycl0[7.1.0.0 ' ]decane, mp 179°-182° uncor ( l i t .  mp 174°-180°).  The f i l t r a t e  separated into an aqueous layer and a pentane layer. layer was extracted once with ether (200 mis).  was  The aqueous  This was then combined  with the pentane layer and washed with water (6 x 200 ml), saturated sodium chloride solution (2 x 200 ml), dried (MgSO^) and removed i n vacuo to give 181.4 g of a c l e a r dark orange-red l i q u i d , bp 51.5°-52.5° at 0.008 mm.  T i c (20% benzene-pentane) indicated the presence of only  one product. ir  Compound 123 showed the following s p e c t r a l c h a r a c t e r i s t i c s :  (neat) 3.46,  6.74,  and 6.69  u; nmr  (CCl^) T 4.47  (broad s, 2,  CH=CH), 7.30-8.53 (m, 10, C. and C_ CH and C_, C , C,, and C, CH.). — — 1 O — / j D / —i. 0  Synthesis of 2-Bromo-3-acetoxy-trans,cis-cyclonona-1,6-diene  (124).  An a c e t i c acid (675 ml) of compound 123 (142 g, 0.507 mole) and AgOAc (87 g, 0.52 mole) was s t i r r e d at room temperature under nitrogen for 48 hrs.  After this period the mixture was f i l t e r e d to remove the  p r e c i p i t a t e d AgBr formed, and diluted with 400 ml of water and 400 ml of ether.  The layers were separated and the aqueous layer was  with ether (2 x 400 ml).  extracted  The combined ether extracts were washed with  water (5 x 400 ml), saturated aqueous NaHCO^ solution (5 x 400 ml), water  (2 x 400 ml) and saturated NaCl s o l u t i o n (2 x 100 ml).  The  - 114 -  ether was  dried (MgSO^) and removed i n vacuo to give 112 g of l i g h t  yellow l i q u i d .  T i c (benzene) indicated that a l l the s t a r t i n g  material (123) was 124 was 5.77  gone and only the acetate (124) was  present.  found to possess the following s p e c t r a l properties:  (C=0)  and 6.08  (HC=CBr) ; nmr y  (CC± ) 4  (m, 2, CH=CH), 4.97  (m, 1, CHOAc), 7.97  8.53  C,  (m, 8, C , 4  C, 5  g  and C  g  4.00  T  Compound  i r (neat)  ( t , 1, CH=CHBr),  (s, 3, 0C0CH_ ), and  4.67  7.53-  3  CH ). 2  Synthesis of 2-Bromo-3-hydroxy-trans,cis-cyclonona-1,6-diene ( 1 2 5 ) . A  solution of 124  (112 g, 0.432 mole) and sodium hydroxide  (18 g, 0.450 mole) i n 700 ml of methanol was ture under nitrogen for 6 hrs.  s t i r r e d at room tempera-  A f t e r t h i s period t i c (10% ether-  benzene) indicated the absence of s t a r t i n g material and the appearance of one new product.  The methanol was  removed i n vacuo, water added,  and the mixture extracted with 200 ml of ether.  The aqueous layer  was n e u t r a l i z e d and extracted with ether (200 ml).  The combined  ether extracts were washed with water (2 x 200 ml) and saturated sodium chloride solution (2 x 200 ml), and dried (MgS0 ). 4  The ether  removed i n vacuo to give 85 g of a wet yellow s o l i d .  This  was  was  r e c r y s t a l l i z e d from ether-hexane, a f t e r treatment with N o r i t , to give 49.5  g of white c r y s t a l s , mp  raised the mp ir  to 88.5°-89°.  (CHC1 ) 2.94 3  CH=CHBr), 4.70 C,, C , C , R  (OH) and 6.12  80°-83°.  Compound 125 (C=C)  (m, 2, CH=CH), 6.03  and C  q  CH„ and C„  A second r e c r y s t a l l i z a t i o n  u; nmr  gave the following s p e c t r a l data: (CC1 ) x 4.20 4  ( t , 1,  (m, 1, CHOH), and 7.50-8.70 (m,  9,  OH). 101  Synthesis of trans,cis-Cyclonona-2,6-dienol of 125  (6 g, 0.0276 mole) i n ether (200 ml) was  (127).  A solution  added dropwise over a  - 115 -  period of 20 min to a s t i r r e d , r e f l u x i n g solution of sodium (11.3 g, 0.492 mole) i n l i q u i d NH^ (200 ml). a d d i t i o n a l 40 min.  The mixture was s t i r r e d  f o r an  Ammonium chloride (30 g, 0.561 mole) was added  followed by 200 ml water.  The layers were separated and the aqueous  layer was extracted with ether (2 x 100 ml).  The combined ether  extracts were washed with water (4 x 100 ml) and dried (MgSO^). ether was removed i n vacuo to give 3.181 g (85%) of a c o l o r l e s s Tic  The liquid.  (20% ether-benzene) indicates that there i s only one new product  present.  A f t e r Kugelrohr  s p e c t r a l data:  d i s t i l l a t i o n compound 127 gave the following  i r (neat) 2.97 (OH), 6.03 (C=C) y; nmr (CC1 ) x 4.144  5.12 (m, 4, CH=CH), 5.80-6.18 (m, 1, CHOH), 6.76 (s, 1, C 7.56-8.84 (m, 8, C^, C  5 >  C  g  Anal. Calcd f o r CgH^O: H, 10.04.  and C  g  OH), and  CH ). 2  C, 78.28; H, 10.14.  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