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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 this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA November, 1971 In presenting t h i s thes is i n p a r t i a l f u l f i l m e n t of the requirements f o r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the L ibrary 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 and study. I fur ther agree that permission f o r extensive copying of 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 representat ives . It i s understood that copying or p u b l i c a t i o n of t h i s thes is f o r f i n a n c i a l gain s h a l l not be allowed without my wri t ten permission. Department of The U n i v e r s i t y of B r i t i s h Columbia Vancouver 8, Canada Date A/OU 3Q . /f7J - i i -ABSTRACT The photolysis of isogermacrone (68) has been investigated. Exclusive "straight" cycloaddition occurs to form syn (70) and anti (71) 1,7-2 6 dimethyl-4-isopropylidene-tricyclo[ ' ]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-di radica l is postulated in order to account for the stereochemistry of the products. The direct and t r iple t - sensi t ized photochemistry of the three geometric isomers of diethyl deca-2,8-diene-l,10-dioate (79 - 81) has been studied. The t r i p l e t reaction is one of rapid cis , t rans isomerization accompanied by slower 2 + 2 internal cycl izat ion in a "straight" manner to give four of the six possible stereoisomeric diethyl bicyclo[4 .2 .0] -octane-7,8-dicarboxylates (82 - 85). The stereochemistry of these products as well as the t r i p l e t nature of the reaction are indicative of a two step mechanism involving 1 ,4-diradical intermediates. Possible explanations for the direct ion of i n i t i a l bond formation i n these reactions are also discussed. The direct (singlet) reaction of the deca-2,8-diene-l,10-dioates i s one of trans to cis isomerization followed by a,3 to B,y double bond migration from the Cis isomer; the sole deconjugated product i s diethyl trans,trans-deca-3,7-diene-l ,10-dioate. A possible explanation for this stereoselectivity i s advanced. Reasons for an investigation of the photolysis of cyclonona-2,6-dienone (128) and a scheme for i t s synthesis are presented. - i i i -TABLE OF CONTENTS Page INTRODUCTION 1 A) Background 1 B) Cycloaddition Reactions 9 (1) Intermolecular Photochemical Cycloaddition 9 (2) Intramolecular Photochemical Cycloaddition 12 a) Acycl ic l 2 b) Cyclic 2 8 C) Photodeconjugation 39 RESULTS AND DISCUSSION 43 A) Isogermacrone 43 (1) Objectives and Choice of Starting Material 43 (2) Photolysis of Isogermacrone 44 (3) Structure Proof of Photoproducts p_ and E 45 (4) Mechanistic Implications 49 (5) Conclusion 52 B) Acycl ic Diene-diesters 53 (1) Introduction 53 a) Background and Objectives 53 b) Source of Starting Material 54 (2) Irradiation i n the Presence of Tr iple t Energy Sen-s i t i z e r s 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 79, 80, and 115 83 a) Photolysis of 7_9_ 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 Irradiation of Compounds •79, 80 and 115 86 (6) Conclusion 88 C) Cyclonona-2,6-dienone 89 EXPERIMENTAL 92 A) General Procedures 92 B) Isogermacrone 93 C) Acyclic Diene-diesters 99 D) Cyclonona-2,6-dienone 112 BIBLIOGRAPHY 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 Dr. J . R. Scheffer. His effervescent attitude towards chemistry and his personal interest i n his students has made this period of learning, in my l i f e , both profitable 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 inte l l igent and fr iendly men as are found i n the Physical-Organic section of this department. Never once was I refused assistance from anyone I approached. I am deeply indebted to the National Research Council of Canada for f inancia l support during the last four years. F i n a l l y , I wish to express my sincere gratitude to my wife Pat for her untiring patience and her excellent work on the diagrams i n this manuscript. - v i -DEDICATION To my w i f e Pat and To my parents Rose E. (Stacey) B o i r e and Anthony A. B o i r e INTRODUCTION A) Background The need to investigate the photochemistry of organic molecules in solution is both synthetic and mechanistic in nature. In the past ten years, photochemical preparative syntheses of unusual carbocyclic and heterocyclic ring systems have become a respectable and often used method. Usually, these systems are extremely d i f f i c u l t to obtain by conventional modes of synthesis. The syntheses of cubane* (Eq 1), the prostanoic acid 2 3 skeleton (Eq 2), and pinacols (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. OH OH \ R R CHOH | | C=0 i - f ^ R. C C R, Eq 3 / h V 1 I I 1 R 2 R2 2^ In order to use organic photochemical reactions more f u l l y , an understanding of their mechanisms is important. The f i r s t step i n any photochemical reaction is the absorption of a quantum of l ight (E = hv) by a ground state ( S Q ) molecule (Eq 4). The i n i t i a l l y formed electronic S Q > Eq 4 s s . > S ] L Eq 5 •f-species i s the vibrat ional ly excited f i r s t singlet state ( S ^ ) which quickly relaxes (Eq 5) especially i n solution phase. Excitation to higher singlet states ( S 2 > S ^ , etc.) 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 l ived —12 A (10 sec) for any processes to occur except radiationless decay to S ^ . If only unimolecular processes are possible the excited singlet state has four possible modes of reaction. Fluorescence (Eq 6) and internal conversion (Eq 7) help to depopulate the singlet state i n approximately 10 sec. These radiative and non-radiative deactivations are of l i t t l e y S Q + hv Fluorescence Eq 6 - 3 -Internal Conversion Eq 7 P Rearrangement Eq 8 Intersystem Crossing Eq 9 interest to the organic chemist as no new product (P) is formed. The excited or "hot" ground state that is formed in Eq 7 i s capable of rearrangement under low pressures, but usually deactivates quickly to 3 starting material in solution. In order for rearrangement (Eq 8) of the state or for intersystem crossing (Eq 9) to occur, their rates must compete effectively with those of fluorescence and internal conversion 8 - 1 4 (10 sec ). There are three mechanisms suggested for the rearrangement of a molecule in the state to a new product molecule (P). The f i r s t one involves a direct rearrangement which produces the excited singlet state of the product, followed by internal conversion to a "hot" ground state. The second mechanism proposes a continuous rearrangement which eventually produces a ground state product. A third p o s s i b i l i t y , which i s not l i k e l y to occur in solution phase, i s rearrangement from the "hot" ground state of the reactant. The last process of intersystem crossing (Eq 9) produces a vibrationally excited t r i p l e t state. This quickly relaxes to T^. The t r i p l e t state cannot be populated directly from the ground state because i t is a spin forbidden process. Thus i t s existence depends on the intersystem crossing efficiency and a process called sensitization which w i l l be described later. In a manner analogous to the - 4 -singlet state, the t r i p l e t i s capable of radiative decay (phosphorescence, Eq 10), nonradiative decay (intersystem crossing, Eq 11) and rearrange-ment (Eq 12) to a new product (P). The t r i p l e t state has a re la t ive ly -4 long l i fet ime (10-10 sec) and thus has more time in which to undergo T^ > S Q + hv Phosphorescence Eq 10 t T^ > S Q Intersystem Crossing Eq 11 T > P Rearrangement Eq 12 reaction. The mechanism by which the T^ state goes on to product is a l i t t l e more complicated than in the singlet case. The direct rearrange-ment and the "hot" ground state pathways are both possible, but the rearrangement from the t r i p l e t state of the starting material to the ground state of the product would involve a discontinuity due to the spin v io la t ion 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 are considered to proceed v i a an intermediate. The primary processes i n organic photochemical reactions discussed so far are best summarized with the aid of a Jablonski diagram"* presented i n Fig 1. Also indicated in Fig 1 i s the fact that an electronical ly excited species can deactivate i t s e l f by interacting i n a bimolecular fashion. These bimolecular reactions follow the Wigner rules'* of spin conservation. Both excited singlet and t r i p l e t states are capable of transferring - 5 -their energy to a ground state molecule. In the former case, an excited singlet acceptor and a ground state donor are formed (Eq 13). In the Fig 1 b and c I ACS ) D(T,) D(Sn) A - acceptor; D - donor a - excitation b - vibrat ional deactivation c - internal conversion d - fluorescence e - intersystem crossing f - phosphorescence g - t r i p l e t energy transfer from D to A (A is sensitized - D is quenched) - 6 -t r i p l e t case, a t r i p l e t acceptor and a singlet 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 in order that e f f i c i e n t 4 exothermic energy transfer be accomplished. The energy transfer mechanism is not well understood. One mechanism involves the transfer of energy over re la t ive ly long distances via dipolar interactions between donor and acceptor molecules. The other more common mechanism to solution photo-chemists involves transfer of energy by direct o r b i t a l overlap. This generally means c o l l i s i o n of donor and acceptor molecules. Both of these processes are predicted to have l i t t l e effect on the overall geometry of 4 the molecules involved. However, certain distorted geometries are often proposed in cases where endothermic energy transfer** appears to be occurring. These bimolecular energy transfer reactions are referred to as sensitization or quenching depending on whether the donor or acceptor molecules are used as reference. Both of these processes are extremely important to the organic photochemist. In order to narrow the topic of bimolecular energy transfer, only t r i p l e t state quenching and sensit ization w i l l be described. One of the most important aspects of organic - 7 -photochemistry is to determine the m u l t i p l i c i t y of a given reaction. In order to do this i t becomes imperative that one i s able to exclusively populate either the singlet or t r i p l e t states of a molecule. Tr iple t sensit ization is capable of putting a molecule into i t s t r i p l e t state with-out going through i t s singlet state. Ketones, and in particular aromatic ketones, are extremely useful in this regard. They have almost unit 3 intersystem crossing eff ic iencies and have high t r i p l e t energies which are capable of sensit izing a wide variety of unsaturated compounds. In this way, analysis of the direct i r radiat ion versus the sensitized reaction may produce meaningful results as in the case of the i r radia t ion of 3,Y~ unsaturated ketones. Direct^ i r radia t ion of 1_ results only in product J2 Eq 15 Eq 16 1 3 (Eq 15), whereas sensitization of 1 results only in 3_ (Eq 16). This i s a good example showing the different reac t iv i t ies of the singlet and t r i p l e t states. Usually, photochemical reactions are not as clear-cut as - 8 -those mentioned above, and often require detailed kinetic data in order to distinguish the react ivi ty of the two electronic states. The conditions for sensit ization are extremely important. In general, a l l the l ight must be absorbed by the sensit izer , and the sensitizer should not undergo any 3 5 chemical change under the reaction conditions. Common sensitizers ' are: benzene (ET= 85 kcal/mole), acetone (E^= 78 kcal/mole), acetophenone (E ,^= 74 kcal/mole), benzophenone (ET= 69 kcal/mole), and naphthalene (ET= 61 kcal/mole). Quenching is essentially the same as sensit ization except in the opposite sense. In other words, a compound i s added that absorbs no l ight under the reaction conditions and is capable of accepting t r i p l e t energy from an excited molecule. In this case the t r i p l e t energy of the quencher must be lower than that of the reactant. Ideally, i f any t r i p l e t state of the reactant is formed during a photolysis, the quencher w i l l interact with i t immediately. Thus i f any rearrangement occurs i t i s proceeding v i a the singlet state of the reactant. These two techniques are often used indiscriminately as an indication of the m u l t i p l i c i t y of a reaction. There are l imitations to sensitization and quenching techniques, and i f not combined with quantum yie ld studies and kinetic data, should only be looked upon as qualitat ive evidence. They can however, be quite convincing as in 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 reaction, i t i s important to know the mechanism involved. While a considerable amount of excellent work has been done on the mechanisms of gas and solution phase i r radiat ions , there are s t i l l many areas where - 9 -mechanisms are speculative and open to different interpretations and hence many areas that should be investigated. One must not only be able to distinguish 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, charge-transfer complexes, transannular interactions, and through-bond interactions. B) Cycloaddition Reactions 9 Cycloaddition reactions form a large part of the f i e l d of organic photochemistry. Even though a considerable amount of work has been done i n this area, the results are often stereochemically unpredictable and mechanistically obscure. In general, this class of reactions can be divided into two main groupings: (1) intermolecular and (2) intramolecular. (1) 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 ring (Eq 17). They have enjoyed the most synthetic use, but paradoxically, simple mechanisms are not available for these reactions. Recently a review"*"^ has been published on enone annelation which i s quite representative of this class of reactions. Usually, substituted enones are photolysed in the presence of excess o l e f i n under conditions where only the enone is absorbing l i g h t . hv Eq 17 - 10 -The excited enone adds to the ground state o l e f i n and, v ia an undetermined pathway, forms a cyclobutane r i n g . The dimerization of eye lop ent enone'''"'' 12 (Eq 18), the addition of cyclopentenone to cyclopentene (Eq 19), and the 13 addition of cyclohexenone to 1,1-dimethoxyethylene (Eq 20) are c lassic Eq 18 hv Eq 19 3HC0^ ^QCH, hv 0 OMe OMe Eq 20 OMe OMe examples of enone annelation. It is generally accepted 1 0 that i t i s the t r i p l e t state of the enone that i s undergoing cycloaddition. Which t r i p l e t state, as enones have low lying mr* and TTTT* t r i p l e t states, i s the reactive species i s uncertain, as evidence for either or both has been found. The immediate question now is how the excited enone reacts with ground state o l e f i n to form product. DeMayo has presented the following scheme'' (Scheme 1) summarizing the postulates to date. Route c involves a 10 - 11 -Scheme 1 K + 0 hv, $ i c K' .3 + 0 KO competitive reactions concerted formation of product. Due to the complex nature of the products formed (Eq 18 and 20) from enone annelation, this mechanistic route appears to have very l i t t l e relevance. However, in simpler olefin 14 dimerizations there seems to be concrete evidence for this pathway. 13 Corey found some regiospecificity in the photolysis of cyclohexenone i n isobutylene, vinyl ethers, ac r y l o n i t r i l e , and ketene acetal. He proposed the formation of an excited state charge-transfer complex (exciplex) 3 between excited enone (K ) and ground state olefin (0) (route a) based on the structure of the product (Eq 21). Cyclohexenone adds to methyl vinyl ether 0 0 0 4 - 12 -to form an exciplex 4_. This exciplex explains the orientation of the sub-stituent i n the product. There are, however, many reactions which would be excluded on exciplex theory alone. It would be d i f f i c u l t to explain the equal ratio of head to head and head to t a i l dimerizations of cyclopentenone (Eq 18). These results tend to favor an interpretation based on the formation 3 of the tetramethylene diradical ['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 for the observed kinetics. Other factors, such as the electrophilicity of the excited enone, dipole-dipole interactions, and the possi b i l i t y of a trans enone inter-mediate have a l l been studied and found to play at least a partial role in 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) Acyclic Unlike intermolecular cycloadditions there are two modes of addition open to acyclic dienes. They are able to add in a "straight" (5) manner hv 5 6 - 13 -to form bicyclo[n.2.0] systems, or in a "crossed" (6) manner to form bicyclo[n.l.l] systems.1"' A p r i o r i , i t would appear that either mode of addition i s equally l i k e l y . However, i t can be shown from experimental evidence that the "crossed" versus "straight" nature of cycloaddition depends on the value of n. Srinivasan studied the mercury sensitized photolysis 1^ of a series of non-conjugated dienes at their boiling points under atmospheric pressure. He found that in the case of 1,4 dienes (7_, _8, and 9) and 1,6 dienes (12) "straight" addition predominated and for 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 his results by a common mechanism, Srinivasan postulated the i n i t i a l formation of a five membered ring followed by closure of the diradical species thus formed to the observed product (Eq 22-24). This empirical "rule of f i v e " i s quite useful and few exceptions are Eq 22 Eq 23 Eq 24 - 15 -known. It does, however, disregard the radical and thermodynamic s t a b i l i t i e s of the intermediates and products respectively. A better explanation is needed to account for the observed speci f i c i t y of i n i t i a l 1,5 bonding. 18 Liu 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_ in the presence of a sensitizer converts them into only 8a and 8d respectively. 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 ratio (5.8 : 1.0) of products was formed irrespective of whether pure 7b_ or _7c was used as starting material (Eq 26). Samples of 7b and _7c taken at incomplete conversions showed that they had not lost their geometric purity. Thus i t appears that a common intermediate i s irreversibly formed. This intermediate - 16 -must account for the ratio of products 9_ and 10_. They suggest that a five products. The authors give a variety of reasons why the intermediate diradical should be long lived. F i r s t l y , the Wigner hypothesis^ indicates - 17 -that the diradlcal should have t r i p l e t character as a result of sensitization and secondly, there should be strain involved in the formation of the cyclobutane ring. In order to explain the unusual stereospecificity in the formation of a five-membered ring, Liu and Hammond suggest that i t i s probably due to kinetic 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 radical s t a b i l i t y increases with substitution. Furthermore, they rejected thermodynamic s t a b i l i t y 20 considerations as thermal equilibration studies favor cyclohexane over methylcyclopentane. They state that "the preference for formation of fi v e -membered rings may merely reflect 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 ring". As added proof for this kinetic control they point out that 5-hexenyl free radicals preferentially 21 form cyclopentylmethyl radicals (Eq 27) even though radical and thermodynamic s t a b i l i t y both favor the cyclohexyl free radical. Only when the radical is highly substituted (R, = COOR, R = CN) does cyclohexyl radical formation Eq 27 predominate. 22 Even though this behaviour of 5-hexenyl free radicals i s quite general 21-23 no satisfactory explanation has yet been given. Liu and Hammond's intermediate (11) has drawn the interest of K. Fukui, 24 - 18 -He calculated the energies of the electronic states of two model inter-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 in one plane while the second •11a H b model (lib) has the C^, axis perpendicular to a common plane shared by carbons C_ , C 0, C„, C_, and C,. Model l i b was shown by extended Huckel 1 2. j J o molecular orbital calculations to be of lower energy than model 11a in 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 for the preference of 1,5 bonding in this system. His major concern is with the fate of the intermediate once i t is formed and not why i t is formed. The t r i p l e t nature of these intramolecular cycloadditions has so far been taken for granted as a result 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 is responsible for 25 26 this phenomenom, the direct (Eq 28) and sensitized (Eq 29) irradiation of myrcene (12) has been done. The small amount of "crossed" product formed under direct photolysis conditions probably results from a limited amount of intersystem crossing of the myrcene singlet. - 19 -Eq 28 Another diene system which has been investigated i s 8-farnesene (13). 27 It was photolysed under direct (Eq 30) and sensitized (Eq 31) conditions by White and Gupta. As in the case of myrcene the direct and sensitized irradiation of 8-farnesene yields different products indicating that - 20 -the "crossed" cycloadditions are primarily originating from the t r i p l e t state of B-farnesene and that the low yield of "crossed" products from the direct irradiation i s a good indication of the intersystem crossing efficiency of the B-farnesene singlet state. It is worthwhile to note that "straight" additon occurs to some extent in B-farnesene under direct irradiation conditions. White and Gupta do not feel that kinetic control of the f i r s t step bas on steric reasons i s sufficient to explain the preference for 1,5 bonding. They reason that since the reaction i s essentially quantitative, the kinetic argument would "necessitate a highly oriented ground state of the substrate". In order to explain the observed speci 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 " in much the same manner as Corey's explanation for the observed 13 speci f i c i t y in cyclohexenone annelation. The excited diene moiety can 13 Eq 32 14 + 15 be considered to have molecular orbitals similar to butadiene. Thus i t w i l l have two electrons in the lowest bonding orbital ty^j one in the second bonding orbital ty^, and one in the lowest antibonding level ty^. The correlation diagram (Fig 2) has the electron in ty^ of the diene inter-acting with the bonding orbital ty- of the olefin moiety and the electron - 21 -113.1 Diene Complex Olefin in of the diene interacting with the antibonding level ty^ of the olefin. Although not specifically stated in the above description of the complex, i t s geometry is suggested to be of a one to one fashion as indicated in structure 16. A l l other combinations lead to rings with greater than six 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 radical 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 rationalizes cycloaddition and indicates a preference for "crossed" over "straight" cycloaddition at least in the case of $-farnesene i t s e l f . Appropriate substituents are often used in order to give a non-conjugated diene an ultraviolet absorption in a region easily accessible - 22 -to conventional light 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 activating group. One of the earliest intramolecular photochemical cycloadditions was 28 29 done by Ciamician and Silber in 1908 followed by Buchi and Goldman in 1957. In this experiment carvone (18) was subjected to California sunlight in a Pyrex vessel for 6.5 months. Carvone-camphor (19) was the Eq 33 only product isolated besides polymer. Another more recent example is the photolysis of 1,5-hexadiene-3-one (20) by Scerbo (Eq 34). "Crossed" product 21 is the only product observed. Both of these 1,5 dienes (18 Eq 34 and 20) exhibit their preference for "crossed" addition. While quenching and sensitization work has not been done on these systems i t is generally accepted that they are proceeding via an excited t r i p l e t state. - 23 -Brown ' in his 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 = CH3 obtained identical results under both direct and sensitized irradiations. Again the empirical "rule of f i v e " seems to hold as "straight" 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 olefin (24) i s attacking the 22a ground state of the other to form a five-membered ring (25). Besides - 24 -obeying the "rule of f i v e " Brown feels that increased conjugation in diradical 2_5_ increases i t s s t a b i l i t y . 33 A notable exception to the "rule of f i v e " was observed by Meinwald in his photolysis of 1,8-divinylnaphthalene (26) and 1,8-distyrylnaphthalene (27). Photolysis of a 0.002 M solution of 26 in cyclohexane gave an 80 -90% yield of 28 and 29_ in a ratio of 10 : 1 respectively (Eq 36) . Eq 36 26 28 29 Similarly, photolysis of a 0.001 M solution of 2_7 in ether yielded 40% and 38% of "crossed" products 3_0_ and 31_ and 5% of "straight" cycloaddition product 32 (Eq 37). These results are quite surprising as "crossed" Eq 3 7 27 30 31 32 cycloaddtion has only been observed as a major pathway in 1,5 dienes. Meinwald explains this unusual spec 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 33 is the most favorable in the ground state and i t is from this conformation - 25 -33 CR = Ph or H) 34 (R = Ph or H) that "crossed" cycloaddition occurs. "Straight" cycloaddition products arise from the less preferred conformer 34. 34 In 1963 Cookson et a l . studied the photolysis of c i t r a l (Eq 38) (a 1 : 1 mixture of c is and trans isomers). Although the major product i s not a cycloadded one, the minor product, photocitral B (35) i s formed in an analogous manner to those previously mentioned. Both products can Eq 38 be rationalized on the basis of i n i t i a l 1,5 bonding (36). Photocitral A (37) can then be formed by 1,4 hydrogen migration and photocitral 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 localized n,ir* t ransit ion 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 extinction coefficient for c i t r a l i s 72 whereas that for g-methacrolein is 25. This is almost a three-fold enhancement. 35 Later in 1968 Cookson discussed i n his Tilden lecture to the Chemical Society the various reac t iv i t ies of the different electronic states of d i a l l y l and i t s derivatives. Compound 3_8 best describes the unique behaviour of the ground (Eq 39), excited singlet (Eq 40), and excited t r i p l e t (Eq 41) states. The f i r s t two reactions are the familiar CN Ground Eq 39 Excited Singlet 38 hv Eq 40 Excited Tr iple t 38 hv (sens.) N C : N Eq 41 Cope rearrangement (3,3-sigmatropic shif t ) and the 1,3-sigmatropic s h i f t 37 36 respectively. Both are well documented. ' The t r i p l e t state i s again responsible for cycloaddition and proceeds in the manner predicted by i n i t i a l 1,5 bonding. This specif ic electronic state behaviour prompted Cookson to construct an energy level scheme (Fig 3) for d i a l l y l u t i l i z i n g the four orbitals of the dienes and the two sigma orbitals of the central - 27 -3 , 4 sigma bond. The levels at the l e f t are uncoupled as they would be in an isolated system. In the middle, the 3 , 4 sigma bond is in a plane at right angles to the plane of both double bonds. The sigma bond then effectively s p l i t s the levels of the IT and TT* states. Cookson f e l t that the levels and ty^* ^ 4 a n d ^ 5 ) could be reversed as this was only a zero order approximation. Fig 3 - 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 interaction brings the highest occupied molecular orbital and the lowest unoccupied molecular orbital closer together. This prediction, he claims, is supported by the ultraviolet absorption of molecules possessing the necessary geometry. On the right (Fig 3) Cookson has drawn the molecular orbitals by increasing the number of nodes from zero to five. He points out that the highest occupied molecular orbital T T s explains the observed Cope rearrangement in the thermolysis of d i a l l y l s . He did not, however, extend this argument to include 1,3 sigmatropic shifts or cycloadditions. Acyclic 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 in 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 this in mind i t w i l l now be necessary to investigate cyclic systems to see i f they behave in an analogous manner. b) Cyclic Cyclic nonconjugated dienes are also capable of adding in a "crossed" or "straight" manner (Eq 42). Much less work has been done in this area and as a result, this discussion w i l l be as complete as possible. Since the question of "crossed" versus "straight" cycloaddition is of immediate - 29 -importance, this discussion w i l l not be concerned with non-conjugated dienes which are constrained geometrically to add in a specific manner. The largest group of such compounds can be illustrated by Eq 43. These Eq 43 dienes react via the t r i p l e t state and usually produce caged ring systems by adding in a "straight" manner. In general, cyclic 1,3 dienes close photochemically to give cyclo-butenes rather than bicyclobutanes. Since the intersystem crossing efficiency of dienes i s low, presumably these reactions are proceeding 39 via the excited singlet state. 1,3-Cycloheptadiene closes in a Eq 44 disrotatory fashion to give bicyclo[3.2.0]-6-heptene (Eq 44). The behaviour of 1,3 dienes under irradiation conditions may be best described as electrocyclic reactions. 40 Acyclic 1,4 dienes usually undergo a di-ir-methane rearrangement as 30 the major reaction pathway. In contrast to this, the results of Moon 41 and Ganz concerning the photolysis of 1,4-cyclooctadiene (39) are quite unique. Under direct irradiating conditions they obtained a quantitative yield of syn tricyclooctane (40). The excited species reacting i s probably the singlet state. A p r i o r i , i t could be said that Eq 44 Eq 45 41 40 could arise v i a i n i t i a l 1,5 bond formation but this does not explain the geometry of the f i n a l product unless kinetic closure of the diradical i s proposed. It has been shown that j40_ is converted into i t s anti isomer 41_ (Eq 45) under thermolysis conditions. Thus the mechanism of 42 2 2 this photolysis would best be described as an allowed IT + ir cyclo-s s addition. Of the 1,5 cyclic 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 solution phase photolysis of 1,5-cyclooctadiene and i t s copper chloride complex (44). In the solution phase he was able to determine that the uncomplexed cyclooctadiene was the principle absorber of the light. This was based on the optical 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 this and 44 deuterium labeling studies Srinivasan postulated an intramolecular mechanism in which 4_2_ absorbs the light, bonds in a 1,5 manner, complexes with copper chloride, and then closes to product (Scheme 2). This scheme shows 42 (as opposed to the cis,trans and trans,trans isomers of cyclo-Scheme 2 - 32 -Scheme 2 - cbnt. CuCl 43 octadiene) as the immediate precursor of product 43. 45 In 1967 Cope and Whitesides synthesized the c is , t rans and trans, 46 trans isomers of 1,5-cyclooctadiene (45 and 46 respectively) . They investigated the photolysis of these isomers i n order to shed l ight on 47 the irradiations 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 , t rans (45) isomer and hints at the possible intermediacy of the trans, trans (46) isomer (See Table 2 and Scheme 3). Unlike Srinivasan, they photolysed 44_ in pentane which results in a heterogeneous mixture. On the Table 2 Substrate Irradiation time (hrs) 42(%) 45(%) 46(%) 43(% 42P 24 100 0 0 0 42b 72 Maj or Trace 0 0 44P 3 93 4 <1 3 44p 24 62 13 -\>1 19 4 4 P 48 28 17 'V'l 43 45p 2 19 0 0 0 45b 20 Major Minor 0 Trace 47P 48 32 ^20 ^1 12 46p 1 0 0 0 70 p - photolysis done in pentane b - photolysis done in benzene - 33 -basis of the qualitative observation that a significant fraction of the c i s , c i s isomer present in the pentane solution of the complex is free in solution, and on the basis of the similarity between their system and that of Srinivasan's, they assumed that 42_ is the primary light absorbing species in the photolysis of a pentane suspension of 44_. Thus based on this assumption and on the data in Table 2 the following mechanistic pathways are suggested for the photolysis of 44_ (Scheme 3 ) . This scheme Scheme 3 44 42 + CuCl CuCl J U L . hv hv,^ + ^ CuCl 46 47 presents the cis,trans copper chloride complex 47^  and 4j6 as the immediate precursors of 43. They present 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 cycloaddition. Neither direct nor sensitized photolysis of 42_ in the absence of copper chloride yields detectable quantities of ^3_. Furthermore, the appearance of 45_ and 46_ under the photolysis conditions (photolysis of 44) and the fact that these in turn can be photolysed to 43 (Table 2) strongly suggest that these are intermediates. Secondly, the relat ive yields of 45 and 43 show that the formation of 43_ depends on the concentration of this diene in solution. This suggests that at least part of the cyclo-addition is occurring from the cis , t rans isomer (45). The high steady state concentration of 45_ during the lat ter stages of the photolysis combined with the re la t ive ly high efficiency with which i t i s converted into tricyclooctane (43) in the presence of copper chloride indicates that a major portion comes from 45_. F i n a l l y , photolysis of 4j[ gives 43 cleanly (70%) and photolysis of 47 yields the trans,trans isomer, and despite i t s consistently low concentration, could give r i se to a significant amount of 43. The authors fee l that the intriguing 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 coefficient of the complexes are in the same ratio as that of the dienes. In such a case one would have "at one extreme of inter -pretation the rates of formation of 43_ from 45_ and precursors should be approximately equal; at the other extreme the major fraction of 43_ might be formed from the trans,trans diene". If this were so, a simple 2 2 mechanism of a concerted IT + ir cycloaddition is conceivable from the s s - 35 -Eq 48 twisted conformation (48) of trans,trans-l ,5-cyclooctadiene (Eq 48). A compound which could conceivably add i n a 1,5 manner to give either "straight" or "crossed" addition would be of considerable interest in order to observe which manner of cycloaddition prevails . One such series of compounds would be the 1,5-cyclononadienes. In 1965 Sutherland photolysed^ byssochlamic acid to give a single cycloadded product (Eq 49). Eq 49 The product, however, was not completely identif ied and i t s structure-proof rests solely 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 non-conjugated 1,6-cyclodecadienes. Based on the empirical rule of 1,5-bonding these can be predicted to add i n a "straight" manner. Late i n 1968 and early i n 1969 three separate papers dealt with the photochemistry of c is ,c is-cyclodeca-3 ,8-diene-l ,6-dione t ^ ,50 ,51 Scheffer and Lungle"^ - 36 -established that the c i s , c i s isomer photolyses to the cis,trans isomer and that this i s the immediate precursor of the ariti "straight" product (Eq 50). hv(Pyrex) Benzene Eq 50 A concerted reaction of the cis,trans isomer to the observed product is not possible and thus the authors suggest a diradical mechanism (Eq 51) Eq 51 49 involving 1,5 bonding with subsequent bond rotation and closure to form 49. Exclusive formation of the anti isomer is explained on the basis of unfavorable steric interactions in the formation of the syn isomer. Here again the po s s i b i l i t y of a trans,trans intermediate is conceivable as the 2 2 42 f i n a l product could then be obtained via a concerted ir + ir cycloaddition. s s Attempts to isolate this intermediate under various conditions, however, 52 have not produced positive results. The multiplicity of the reaction is probably the t r i p l e t state as i t has been observed that the reaction 52 proceeds in the same manner under sensitization conditions. 53 A less specific cyclization was observed by Heathcock in his - 37 -attempt to enter the copaene ring system via a cyclodecadienone (50). Photolysis of 50_ (double bond isomers of unknown geometry) in ether led to both "straight" (51 and 52) and "crossed" (53) cycloadded products in Eq 52 - 53C22%) a 35 : 22 ratio respectively. These results are quite unique as a significant amount of product (53) arises via i n i t i a l 1,6 bonding. Germacrene D (54), a naturally occurring sesquiterpene was photolysed"''' by Yoshihara et a l . This compound is potentially 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) in a "straight" or "crossed" manner respectively. Irradiating 54 under direct conditions led mainly to (-)-8-bourbonene (55) and minor amounts - 38 -of a-bourbonene and 6-copaene (Eq 53). Possibly, more copaene would 56 have been formed had the photolysis been done under t r i p l e t conditions. In order to explain the transannular interactions (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 in the ring are situated par a l l e l and face to face with each other. The three substituents are orientated in the same direction 3 to the ring. It is from conformation 5_6 that Yoshihara explains his photolysis and thermolysis results of germacrene D. A closely related system i s the photolysis" 5^ of isabelin (Eq 54). Here we have a 1,5 diene which adds in a "straight" manner but careful analysis of molecular models indicates that the resulting product derived 56 0 Eq 54 57 from "crossed" cycloaddition would be severely strained due to the presence - 39 -of the lactone ring. Sondheimer has reported the photocycloaddition of the largest cyclic 58 diene (58) system. The addition proceeds readily on exposure of 58 2 2 to sunlight and can be looked upon as a concerted photochemical TT + TT s s hv cyclo-hexane ^\ Eq 55 cycloaddition. The structure proof of product 59, however, is not unequivocal and no multiplicity studies were carried out. As can be seen from this survey, very l i t t l e has been accomplished in understanding the mechanisms of cyclic photochemical cycloadditions of non-conjugated dienes. There remains much to be done in this 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 position. While this phenomenon has been observed in acids . . 60,61 , _ 62-65 . « . fc , ketones and esters, only the latter appears to have been 62 studied to any extent. In 1968, Barltrop and Wills"" sought to find a mechanism which would explain deconjugation. Irradiation of the trans compound J5_0 under direct conditions led to a rapid interconversion of cis and trans isomers (Eq 56). - 40 -This was followed by the formation of the 3,Y isomer (62). Photolysis of the c is isomer was almost identical except that no induction period for the formation of 62 was observed. Irradiation under t r i p l e t conditions H COOEt CH 3 COOEt J00Et \ / hv > \ / hv . ^ / A A ^ " A A CH„ H H H — Eq 56 60 61 Cbenzophenone, acetophenone, and acetone) led to c is , t rans isomerization but no photodeconjugation was observed. Barltrop feels that i t i s the 62 n,Tr* singlet that i s responsible for deconjugation whereas i t i s probably the n ,Tr* t r i p l e t state doing the cis 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 3 COOEt C H 2 c _ 0 E t .c \ / hV S > ' v . > ' A A A A A A H H H H H H HO COOEt . v . \ - 41 -This mechanism is supported by the fact that the double bond must be in the cis configuration in order for deconjugation to occur. The mechanism is further supported by the fact that when ethyl crotonate is photolysed in methanol-OD the products contain at least 97% of one deuterium at the carbon atom adjacent to the ester group. There i s also a solvent effect i n which the reaction proceeds faster i n alcoholic solvents. This may either be ah effect on the quantum efficiency of the intramolecular hydrogen abstraction leading to the dienol or the ease of ketonization of the dienol to the 8,y isomer. 63 At the same time Jorgenson confirmed these results by studying the photolysis of 64. Only cis to trans isomerization was observed under Scheme 5 sensitized conditions but under direct i r radiat ion conditions j>6 and 67 were also formed (Scheme 5) . Jorgenson f e l t that j56_ (deconjugation) was coming from the singlet state of the c is 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 feels supports the dienol intermediate formed via an intramolecular hydrogen transfer (Scheme 4). Further support for the dienol intermediate in photodeconjugations comes from the work^1 of Noyori et/al_. on the photolysis of an o t , 3 -unsaturated ketone (Eq 57). Dienols 6_5 and 66 were formed in 80% yield OH C\ ^ C 0 C H 3 J 67 in a ratio of 5 : 1 respectively. Heating the dienol mixture at 100° for 2 hr afforded deconjugated product (67) and starting material (64) in an 83 : 17 ratio respectively. Early in 1968 Rando and Doering studied the photodeconjugation of a 59 series of substituted a,3-unsaturated esters and acids (Eq 58). They R i 0 Rn 0 ^CH-CH=CH-C-0R(H) — * C=CH-CH -C-OR(H) Eq 58 R2 R2 observed, in the case of the acids (R- = n-C-H n„, n-C^H1c, and n-C 1 0H 0 C; R 2 = H), that both cis and trans 8,y-unsaturated products were formed. A trans to cis ratio of 2 : 1 was observed for these reactions. - 43 -RESULTS AND DISCUSSION A) Isogermacrone (1) Objectives and Choice of Starting Material Before 1969 the photochemistry of nonconjugated medium-sized ring dienes was essentially an untouched area of research. With the exception 42-47 of some extensive work done on 1,5-cyclooctadiene and 3,8-cyclodeca-49-51 41 53 diene-l ,6-dione only two other compounds ' were photolysed in which the f i n a l products were characterized. Thus a further investigation in this area promised to be both interesting and useful . The choice of a starting material was based on three properties which i t must possess: 1) a nonconjugated medium ring c y c l i c diene, 2) an easily accessible ul t raviole 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. It has a basic 1,6-cyclodecadiene skeleton, an easily accessible ul t raviole t region (uv max 334 nm, log e 1.923)^ and can be prepared in one step from the 66 naturally occurring sesquiterpenone germacrone (69). Generous samples of germacrone were received from Dr. M. Suchy, Czechoslovak Academy of - 44 -Science, and Fritzsche Brothers, Inc., New York, N.Y. Germacrone was converted to isogermacrone under basic conditions in reasonable yields. A solution of germacrone in 0.5 N alcoholic potassium hydroxide was refluxed for four hours (Eq 59). This gave after conventional workup Ethanol A, 4 hrs • 5 N K 0 H -> I I Eq59 69 68 procedures, followed by column chromatrography, pure crystals of isogermacrone, mp 48° - 50° ( l i t . ^ mp 51° - 52°). The geometry of the C . C and c . C„ double bonds in germacrone have been established 3' 4 7' 8 6 67 by nmr observations to be trans with respect to the cyclodecane ring. However, in isogermacrone while the geometry of the C^, double bond is probably trans only the trans configuration of the C.,, C 0 double bond 7 8 i s known with c e r t a i n t y . ^ Isogermacrone, prepared by the above method, is a single isomer as indicated by various t i c and vpc experiments. The spectral data (mass spectrum, i r , and nmr) are in 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 in 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 purified by preparative vpc. Compounds A, IS, and C_ were found to be too v o l a t i l e to permit isolation. Compounds F_ and G_ were collected in sufficient amounts by preparative vpc to obtain crude spectral data. (3) Structure Proof of Photoproducts D_ and E Spectral data ( i r and nmr) of D_ and E indicated the absence of any vinyl hydrogens and the presence of a ketone and an isopropylidene group. Mass spectra and elemental analyses confirmed their isomeric relation-ship with starting material. On the basis of this preliminary evidence i t was concluded that cycloaddition had taken place between the C^, C^ and the C.,, C Q double bonds. There are two possible modes of cycloaddition available to isogermacrone. "Straight" bonding, derived from i n i t i a l 1,5-bonding, produces two possible isomers 7_0 and 7_1. "Crossed" bonding, derived from i n i t i a l 1,6 bonding gives only the symmetrical structure 72. The poss i b i l i t y of structure 7_2 was discounted on the basis of spectral evidence (mass spectrum, i r , and nmr). The mass spectra of p_ and E showed large peaks at m/e 96 and at m/e 122 corresponding to cleavage of the 450 W Hanovia C (2.4%) + p (48.4%) + E (29.5%) + F (5.2%) + G (9.4%) hv,N2,Pyrex A (0.5%) + B (4.5%) +. Eq 60 68 - 46 -cyclobutane ring in structures 70_ and 7_1. Furthermore, there is no common fragmentation pattern between the mass spectra of p_ and _E, and that of 70 71 72 ylangene and copaene; the latter two have the basic tricyclo[]-decane skeleton as in 72. The infrared spectra of p_ and E_, which were very similar, showed strong absorptions at 5.88 u (carbonyl) and at 6.14 u (isopropylidene). The peak heights of these absorptions are approximately equal and can be attributed to a five-membered ring structure as present in structures 70 and 7_1 (See Fig 4 ) . ^ in structure 77 the carbonyl absorption would Fig_ 4 (a - Intensity of infrared C=0 stretch/Intensity of infrared C=C stretch) be expected on the basis of the data in Fig 4 to be around four times more intense than the isopropylidene stretch. Further confirmation of a five-membered ring 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^2 methyl singlets. 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^2 methyl groups are relatively far from the effects of the carbonyl as determined by molecular model examination. However, in structure 7_1 both the and the methyl groups should be significantly s hielded^ by the anisotropic effect of the carbonyl. On the basis of this observation p_ [partial nmr (CDC13) T 8.81 (s, 3, C 1 2-CH 3), and 8.92 (s, 3, C^-CH^] and E [partial nmr (CDC13) T 9.10 (s, 3, C 1 2 ~ C H 3 ^ ' a n d 9 , 1 7 3 ' C n ~ C H 3 ^ w e r e assigned structures 70_ and 71_ respectively. In both cases the downfield methyl signal was assigned to the more remote C^2 methyl group based on a similar argument of carbonyl shielding. Unequivocal proof of structure was derived from an independant synthesis of 70_ and 71. Use was made of the well known photochemical addition of enones to alkenes (enone annelation).^ In this case Eq 61 74 - 48 -cyclopentenone was photolysed in an excess of 1,2-dimethylcyclopentene to give a 5 : 3 mixture of photoadducts 7_3_ and 7_4 respectively (Eq 61) . The gross structures of 73 and 7_4 were verified by mass spectra, i r , and nmr. The nmr also supplied the information needed in assigning the syn or anti configuration. The major product [partial nmr (CDCl^) T 8.55 (s, 3, C 1 2-CH 3), and 8.93 (s, 3, C^-CH^)] and the minor product [partial nmr (CDC13) T 8.99 (s, 3, C ^ - C H y , and 9.11 (s, 3, C^-CE^] were assigned the structures of _73_ and 74_ respectively. Similarly, based on the argument of the shielding influence of the carbonyl, the downfield singlet was assigned to the more remote C^ 2 methyl group. Two approaches were taken in order to extablish the structures of photoproducts D_ and 15 as 70_ and 7_1_ respectively. The f i r s t of these involved the sodium amide alkylation 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 spectral data ( i r , nmr, and mass spectra) Fig 5 ethyl acetate H 2-Pt0 2 NaNH, D isopropyl bromide 73 75 E ethyl acetate H 2-PtO ? > isopropyl bromide Na NH2 74 76 - 49 -showed the products obtained from each method to be quite similar, there were enough differences to warrant further evidence. These slight differences could arise from the fact that the isopropyl group i s capable of existing in either the endo or exo position. Undoubtably 7_5 and 76 synthesized by the above procedures are a mixture of these two stereoisomers. The second attempt involved the direct synthesis of 70 and 71. Adducts 7_3 and 74_ were condensed with acetone in the presence of excess 72 sodium ethoxide. Compounds 70 and 71 prepared in this manner from Acetone NaOEt-EtOH Acetone NaOEt-EtOH 71 and E 73 and 1J\_ respectively were identical ( i r , nmr, mass spectra, vpc retention times) to photoproducts p_ and 12 isolated from the photolysis of isogermacrone. (4) Mechanistic Implications The major products derived from the photolysis of isogermacrone can be formally explained as arising 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 spectral properties of the minor products (F and G) indicate unsymmetrical type products incompatible with the symmetrical "crossed" compound 72. The poss i b i l i t y of photoproducts 70_ and _71 arising via a concerted 2 2 TT + TT cycloaddition offers no explanation for the formation of both s s syn and anti tricyclodecanes. As there is no evidence of any geometric isomers of ji8_ forming during the photolysis, a concerted pathway appears very unlikely. The formation of both possible "straight" cycloadducts could be interpreted as indicating a two-step mechanism involving a diradical intermediate (77 or 78) which i s capable of closing in two different Scheme 6 70 + 71 ways to yield the observed products _70_ and 71^ (Scheme 6) . Presumably, based on known radical s t a b i l i t i e s , diradical 78_ would be the most li k e l y intermediate energetically. The preference for formation of 7_0_ - 51 -could then be explained on the basis of less steric hindrance in i t s formation. Molecular models support the idea that the two methyl groups in a syn relationship to the cyclopentenone ring involves more steric interactions than the methylene groups of the cyclopentane ring in a similar syn relationship. It appears l i k e l y that both methyl groups are needed to affect the product distribution. Heathcock and Badger find a 53 10 : 1 ratio of anti to syn products in the photolysis of 6-methyl-l,6-cyclodecadien-3-one (Eq 52). Further evidence for the influence of the two methyl groups on product formation comes from the 5 : 3 ratio of syn to anti products formed in the photoaddition of 1,2-dimethylcyclopentene to cyclopentenone (Eq 61). This exclusive "straight" cycloaddition for cyclic 1,6-dienes i s 50 51 54 55 in accord with those reported. ' ' ' The major exception to this is worthy of note. Heathcock and Badger photolysed 6-methyl-l,6-cyclo-decadien-3-one (Eq 52) which is structurally similar to isogermacrone. In ether 5 3 they obtained a mixture of 51 (32%), 52^  (3%), and 53 (22%). In 54 hexane solution they obtained a 51_ to 5_3_ ratio of 2 : 1. However, under the same photolysis conditions cyclodecadienone _50_ yields a _51_ : 5_3_ ratio of 9 : 1. This result strongly indicates a t r i p l e t precursor for "crossed" product 53. This seems to be in accord with multiplicity results obtained 26 27 for "crossed" product formation in the photolysis of 1,5 dienes. ' However i t cannot be concluded on the basis of this data that the t r i p l e t excited state i s not responsible for "straight" cycloaddition products 51 and 5_2. There is ample evidence especially in 1,6 and 1,7 dienes that the t r i p l e t state i s the excited state responsible for "straight" cyclo-- 52 -addition. ' Unfortunately the photolysis of isogermacrone cannot shed any light on this problem as the excited state species responsible for exclusive "straight" addition is at present unknown. (5) Conclusion It i s evident that more work in the area of the photochemistry of cyclic nonconjugated dienes is necessary. Many factors concerning the nature of the cycloaddition are s t i l l in doubt. Why does compound 50_ give a reasonable yield of "crossed" product? Why do a l l other cyclic 1,6 dienes give only "straight" addition products?^"* Are the "straight" and "crossed" products coming from the same excited species? These are only a few of the questions that s t i l l have to be answered. Two things however, remain f a i r l y certain: Cyclic 1,6 dienes in general prefer to cycloadd by i n i t i a l 1,5 bonding and give products indicative of a two-step mechanism. - 53 -B) Acyclic Diene-diesters (1) Introduction a) Background and Obj ectives Acyclic non-conjugated dienes are capable of photochemically cycloadding to form bicyclo[n.2.0] or bicyclofn.1.1] systems, where n is the number of carbon atoms between the double b o n d s . T h e "rule of five"'''^ predicts "straight" bonding for systems with n = 1 and 3, and "crossed" bonding for systems with n = 2 (Eq 62). Experimental results 9 in general support these predictions quite well. Up u n t i l 1969, when the Eq 62 "Straight"(n = 1, 3) "Crossed"(n = 2) present project was begun, no acyclic diene system with n = 4 (i.e., a 1,7-diene) had been studied. By investigating the photochemistry of acyclic 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 olefin moieties, and the s t a b i l i t i e s of the rings formed may be more important as n is increased. In diene systems with n = 5 or greater, however, molecular models indicate that there may be no distinction between a "crossed" or "straight" cycloaddition mechanism. If n is sufficiently large i t would be impossible to determine whether a - 54 -bicycle-[n. 1.1] system was formed via "crossed" or "straight" bonding (Eq 63). In these cases, the olefin moieties would have to be looked Eq 63 upon as isolated double bonds. With n = 4 there are too many non-bonding interactions for a "straight" cycloaddition mechanism for the formation of a bicyclo[n.l.l] system. Thus a 1,7 diene would make an ideal starting material for the investigation of acyclic photochemical cycloadditions where the "rule of fi v e " is inapplicable. The compounds chosen for this investigation were the geometric isomers of diethyl-2,8-decadiene-l,10-dioate (79, 80, and 81). OOEt OOEt 79 OOEt COOEt COOEt COOEt b) Source of Starting Material Diene-diester ]9_ has an easily accessible n,7r* ultraviolet absorption 73 (uv max 241 (e 410) nm) region and can be easily prepared by known 74,75 literature procedures. Sebacic acid (1,10-decanedioic acid) was - 55 -converted into i t s diacid chloride (Scheme 7) by heating at 90 in a slight excess of thionyl chloride. The diacid chloride was photobrominated by the dropwise addition of bromine in the presence of lig h t . The resulting Scheme 7 COOH S0C1. COOH COOEt -COOEt DMF 79 'C0C1 -C0C1 Br 1) hv, 2) Ethtnol 2' 74 mixture was esterified with absolute alcohol (Scheme 7). The dibromo-diester was then converted to 7_9 by refluxing in dimethyl formamide.75 Diene-diester 79, bp 104° at 0.02 mm ( l i t . 7 5 bp 127° at 0.28 mm) was characterized by i t s spectral properties which w i l l be discussed later. A small amount of the cis,trans isomer J50 was also obtained by the above method but i t was found more practical to synthesize this isomer and isomer 81 by photochemical means. (2) Irradiation irt the Presence of Triplet Energy Sensitizers a) Photolysis ©f 79_, 80, and 81 Diethyl trans,trans-deca-2,8-diene-l,10-dioate (79) (5 mmol in 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 sensitizer and solvent (Scheme 8). Under these conditions greater than 98% of the light was absorbed by the acetone (See Experimental). The course of the reaction was followed by analytical 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 ratio of 7_9 : 80 : 8>1 remained constant at 3.8 : 3.5 : 1.0 throughout the photolysis (from 6% to 94% conversion to the f i n a l product mixture). A similar equilibrium mixture of 7_9 - 81_ was formed using acetophenone (E^, = 74 kcal/mole) as sensitizer (benzene solvent, Pyrex f i l t e r ) . Continued irradiation similarly gave 82^  (45%), 83 (16%), 84_ (31%), and 85 (8%). Benzophenone was also found to sensitize cyclization but naphthalene failed to produce any change in 7_9 during irradiation. Diene-diesters 80_ and 81_ were isolated by preparative vpc. Their characterization w i l l be described in the section concerning the direct irradiation of the diene-diesters 7_9 and 80. Diene-diester 80_ was photolysed in the presence of acetone and gave an identical equilibrium mixture of 7_9_ - j?l_ as in the sensitized irradiation of 19_ (Scheme 8). Continued irradiation gave photoproducts 8_2_ - 85_ in the following yields: 82 (44%), 83 (18%), 84 (31%), and 85 (7%). Diene-diester 8JL similarly, upon acetone sensitization, gave a mixture of 79 - 81_ (Scheme 8). However, an equilibrium mixture was never obtained and continued irradiation gave photoproducts S2_ - 85_ in slightly different 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 vinyl hydrogens and the i r spectra showed the presence of a saturated ester carbonyl. In order to determine the specific structures of the photo-products 82, 83, and 84 their independent systhesis was undertaken. By - 58 -the method of de Mayo,77 diethyl maleate was photolysed in the presence of an excess of cyclohexene (Eq 64). The photoadducts corresponding in vpc -COOEt hv 82 + + 83 84 Eq 64 Other products 77 *COOEt retention times to 82, 83, and 84_ were collected by preparative vpc and found to have identical spectral properties to 82_, 83, and 84_ formed in the sensitized photolysis of 7_9_ - 81. Additional support for structures 82, 83, and 84 came from their hydrolysis to the known dicarboxylic a c i d s . 7 7 . The hydrolysis of j$2_ gave trans,anti, trans-bicyclo [4.2.0] octane-7,8-dicarboxylic acid, mp 180°-182° ( l i t . 7 7 mp 181°-182°)(Eq 65). Similarly, 83 afforded cis,trans-bicyclo[4.2.0]octane-7,8-dicarboxylic acid, mp 197°-kC00H 82 NaOH H20 Eq 65 COOH - 59 -84 NaOH H20 COOH COOH Eq 67 198° ( l i t . 7 7 mp 199°-200°) (Eq 66), and 84 gave cis,anti,cis-bicyclo[4.2.0]-octane-7,8-dicarboxyxlic acid, mp 170-172 ( l i t . mp 174 -176 ) (Eq 67). c) Thermodynamic Stab i l i t i e s of Photoproducts 82 - J35_ In order to establish the structure proposed for 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 results of base catalysed epimerization experiments. It 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 catalytic amount of sodium ethoxide in absolute alcohol in a sealed v i a l for 12 hrs at 80°. Four products, corresponding in vpc retention times to j32, 83_, 84_, and 85_ were formed (Eq 68). The ratios of 82 : 85 and 83_ : 84 were 90 : 10 and 85 : 15 respectively. Compounds 82 .COOEt 83(50%) COOEt .COOEt COOEt 85(50%) — I N a°Et > 8 2 ( 4 5 % ) + 83 (42 .5%) EtOH Eq 68 +84 (7.5%) + 85 (5%) - 60 -COOEt 82 (87%) + 85 (10%) + unknown (3%) Eq 69 COOEt 82 COOEt NaOEt EtOH 83 (86%) + 84 (14%) Eq 70 V 'COOEt 84 and 84_ prepared in this manner were identical ( i r , nmr) to those previously observed. Photoproduct 82, under similar basic conditions gave an 87 : 10 : 3 rat io of three products (Eq 69). The f i r s t was shown to be starting material 8_2_ (vpc retention time, i r , nmr) and the second to be isomer 8_5 (vpc retention time and i r ) . The third product was not isolated. Under ident ical conditions 84_ gave an 86 : 14 rat io of two products (Eq 70). These were shown by spectral data ( ir and nmr) and vpc retention times to be compounds 83_ and 84_ respectively. These results from the base catalysed epimerization of 82_ (Eq 69) and 84_ (Eq 70) c learly indicate that in 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_. These conclusions confirm the structure proposed for photo-product 85. These results also established j32_ and 83_ as the most thermodynamically stable isomers in the trans and c is series respectively. Additional support for these s t a b i l i t y results came from the thermolysis of photoproducts 82, 83, and 84. Diester 84 was heated in a sealed tube - 61 -at 250 . After 28 hrs there was no change in the 83_ : 84^  ratio of 81 : 19 (Eq 71). Both products were characterized by their spectral 84 83 .COOEt COOEt .COOEt COOEt 28 hrs — 83 (81%) + 84 (19%) 62 hrs — 83 (82%) Eq 71 84 (18%) Eq 72 82 .COOEt COOEt 88 hrs 5 products in following ratios: 1.1(82) : 1.0 : 3.3 : 1.6 : 1.2 Eq 73 properties ( i r , nmr) and vpc retention times. These were the only two products with the exception of diethyl maleate and cyclohexene (based on vpc retention times) present in less than 1%. Diester 83_ under identical conditions gave a mixture of 83 (82%) and 84 (18%) after 62 hrs (Eq 72). Diester j52_ i n i t i a l l y appeared to give the same products as in i t s base catalysed epimerization (Eq 69) but after 88 hrs gave 5 products in the ratio 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 identified. - 62 -(3_) Discussion of Sensitized Photolyses of 79, 80, and 81 a) Possible Mechanisms The equilibrium mixture of dienes 7_9, J50, and 81_ formed in the sensitized (acetone, acetophenone) photolysis of compounds 7_9 and 80 indicate a cis,trans isomerization that i s faster than cycloaddition. In the case of the photolysis of diene-diester 81_, an equilibrium mixture of _79 - £51 i s not reached as cycloaddition appears to be at least competitive with cis to trans isomerization. Thus i f the geometry of the double bonds affects the products formed, then one would intuitively expect a different ratio of photoproducts in the photolysis of j$l. This i s in fact shown to be true experimentally. There are two general types of mechanisms usually postulated for 42 photochemical reactions. The f i r s t involves a symmetry allowed process resulting in the stereospecific formation of products via a concerted mechanism. The second involves a two or more step process having distinct intermediates. The intermediate may be diradical or ionic, and product formation is often non-stereospecific. In order to determine what one might expect from these two types of mechanisms i t would be helpful 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 (Eq 74) one would expect only products 86_ and 87_. The relative yields of these products may or may not be in line with their thermodynamic s t a b i l i t i e s . More important is the steric hindrance involved in the geometry of approach of the two olefins. 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. If the intermediates are sufficiently long lived the products are usually formed in amounts corresponding to their thermodynamic 18 79 s t a b i l i t i e s . Sometimes kinetic control ' in the formation of the inter-mediate or of the product may be an important factor in these reactions. Sometimes both concerted and stepwise mechanisms are operative in the same 80 reaction and detailed kinetic data is 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 photo-2 2 chemically cycloadding in a TT + TT fashion to give two products. Since s s 2 2 the olefins are in a relatively small acyclic chain, TT + TT cycloaddition c l 3-appears to be s t e r i c a l l y unlikely. Diene-diester 7_9_ is capable of giving in a concerted fashion cycloadded products 8_2_ and 8_4. Similarly, 8_0 and 8_1 - 64 -Eq 76 Eq 77 Eq 78 can concertedly give rise to photoadducts 83 and _85 (Eq 77), and 92 and 93 (Eq 78) respectively. If this were the only mechanism operative one would expect a 46% yield of 82 + 84, a 42% yield of 83 + 85, and a 12% yield 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 fact, however, in the photolysis of 79_ and 80, 78% of J32 + 84 and 22% of 83 + 85 are formed. No 92 or 93_ is ever found to be present even when pure 81_ is used as starting material. In this latter case an equilibrium mixture - 65 -of _79_ - 81_ was never achieved and thus a similar prediction of product distributions is impossible. Experimental evidence thus points away from a concerted mechanism. In the case of a di radical or ionic 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 is fused products j$3_ and 84 (95). 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 in nature as equal amounts of c is and trans fused products are formed. Intermediate 94_ can exist i n two different confor-mations ( i . e . , the e,e and a,a conformation). Since bonding is only possible from the e,e conformation only this w i l l be considered i n the following discussion. 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 se to photoproducts 82_, 85_, and _93_ while intermediate 95 can bond to give 83_, 84_, and 92. Each of these p o s s i b i l i t i e s w i l l be considered separately. 81 Intermediate 94_ may be regarded as a vibrat ional ly deactivated t r i p l e t 1,4 di radical which spin inverts to the singlet excited state and then bonds to form trans fused bicyclo[4.2.0]octane systems. As the 94 (e,e + a,a) 95 (e,a) •» +, or -- 66 -radicals approach each other for bonding (i.e., approaching the transition state), non-bonded interactions are encountered between and (a,6 interaction), between C ^ Q and (a,6), and between and C ^ Q (a,a interaction). These interactions (Scheme 9) are expected to determine Scheme 9 82 85 93 the relative 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 in greater amounts than isomers 85_ or 93. Closure of 94_ to give both &5 and 93 involves two steric interactions (a,6 and a,a) (Scheme 9) and the effect of this on their relative distribution should depend on the magnitudes of the a,6 and a,a interactions as the transition state i s 79 approached in each case. Previous work on the photolysis of the geometric isomers of dimethyl-2,7-nonadiene-l,9-dioate indicate that - 67 -a,6 effects are stronger than a,a effects as the 2,8 bond begins to form (Eq 79). Photoproduct 98 whose formation from intermediate diradical 97 COOMe hv i ^-^COOMe .COOMe COOMe COOMe + COOMe C^OOMe Eq 79 COOMe 96 97 98 99 involves one a,a interaction, i s favored by a factor of three over photo-product 99^ , whose formation involves one a,6 interaction. These results tend to support the experimentally observed formation of photoproduct 85 (one a,6 and one a,a interaction) i n preference to isomer 93_ ( two a,6 interactions). Photoproducts 82 and 8_5 are formed in a ratio of 6 : 1 and none of isomer 93 was detected. Fortuitously, the product ratio i s also in line with the relative thermodynamic s t a b i l i t i e s of the various photo-products. Base catalysed epimerizations of 82_ (Eq 69) and 85_ (Eq 68), which only involve avoidance of a,a interactions, both give an 8_2 to 8_5 ratio of approximately 9 : 1 . Intermediate 95_ which i s the immediate precursor of the cis fused 81 bicyclof4.2.0]octanes, can also be looked upon as a vibrationally relaxed t r i p l e t 1,4 diradical which spin inverts to the singlet state and then bonds. The same type of non-bonded interactions (a,6 and a,a) are involved in the transition state as the diradical starts to bond (Scheme 10). Formation of photoproduct £33_ involves one a,6 interaction while the formation of isomer 84 involves one a,a interaction. This i s very similar - 68 -to the formation of 99_ and 98_ respectively in Eq 79. On this basis, formation of photoproduct 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_ ratio in the photolysis of ]9_ and 8 £ was approximately 2 : 1 . Formation of isomer 92 involves two a,6 and one a,a interaction, and thus the activation energy for i t s formation would be expected to be quite high relative to the formation of 83_ and Experimentally, no 92_ is observed. The product ratio in the formation of the cis fused series i s not in line 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_ : ratio becomes approximately 17 : 3. It i s interesting to note that the mixed cycloadditions of diethyl - 69 -and dimethyl maleate to cyclohexene are not governed by the same factors as in the photolyses of _79 and 80 and thus different product ratios are observed (Eq 80). In these cases the a,a interactions are far more important than a,6 interactions i n the closure of diradical species 100. The reason for the increased effect of the a,a interaction stems from the fact that the C^t Cg bond i s already formed and thus the C^ and C ^ Q groups R00C> R00C hv a -~C00R 100 I—^C00R a R = Me or Et 00R 'COOR 12% 28%(82) N-C00R Eq 80 COOR 6% 0% feel each other (a,a) more than the C^ and C ^ Q carbons as the Cg, C^ carbons begin to bond. This explains the preference for trans carboethoxy groups i n both cis and trans fused bicyelo[4.2.0]®etane systems (Eq 80). The preference for cis fused bicyclo[4.2.0]octane products (R = Et, 72% c i s ; R = Me, 82% cis) can be attributed to the relative s t a b i l i t i e s of cis 82 and trans fused bicyclo[4.2.0]octane systems. These arguments based on a kinetic closure of diradical j)4_ and 95 explain the relative amounts of products j32 - 85_ formed in the sensitized - 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 result of the anomalous product ratio that i s observed when pure 81_ i s used as a starting material. The major difference involves the preference for formation of cis-bicyclo-[4.2.0]octane systems over the corresponding trans fused systems. Instead of a cis/trans ratio of almost unity the photolysis of 81_ produces a ratio of almost 2 : 1 . This change is mainly brought about by the increase of photoproduct 84_ and the decrease of photoproduct 82. In order to explain these results in a satisfactory manner i t would be necessary to propose a unique mechanism for 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 for 12% of the f i n a l product mixture. Thus i t is not too far wrong to consider the photolyses 79_ and 80_ as being separate from the photolysis of 81. However, in the photolysis of pure 81_ an equilibrium mixture of diene-diesters is never reached and 8_1_ is always present as a major component in the 7_9 - 8_1 mixture. Since the product ratios are in the same direction as observed in the photolyses of _79_ and 80 (i.e. , j*2_ and 84_ are formed in greater amounts than 8_5 and 8_3_ respectively), then i t would seem l i k e l y that i n i t i a l bond formation is the differing factor operating. A ground state complex such as that shown in 101 would favor the formation of 9_5 and hence lead to more cis fused products. It i s also conceivable that an excited state complex of similar geometry could be formed in the photolysis of the ci s , c i s isomer - 71 -COOEt / COOEt T COOEt \ COOEt 101 102 81. This argument, based on exciplex formation, i s analogous to Corey's 13 explanation for the stereospecific photocycloaddition of cyclohexenone 27 to methoxy ethylene (Eq 21) and White's reasoning for the direction of photocycloaddition in 3-farnesene (Eq 30). While such a complex (101) explains the results, the reason for such a complex i s unclear. Molecular model investigation does not indicate any obvious preference for a conformation such as that in 101 over a complex such as that in 102 which would lead to the trans intermediate 94_. As can be seen, a simple explanation for the preference for cis fusion in the photolysis of diene—diester 8_1 is not available at present. It is s t i l l f a i r l y certain however that the photolysis of 81_ is proceeding via a tr i p l e t diradical intermediate as is 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 selectivity of the i n i t i a l bonding step in photochemical cycloadditions of acyclic and cyclic non-conjugated dienes. Each of these explanations possesses certain merits in individual examples, but usually cannot be extended to other systems. The most widely used guide to these cycloadditions i s that a five membered ring i s formed f i r s t . This was proposed by Srinivasan and 16 Carlough and is better known as the "rule of five". While this mnemonic - 72 -does indicate the direction of cycloaddition in 1,4- 1,5- and 1,6 dienes, i t i s inapplicable in the case of 1,7 dienes. Furthermore, i t is s t r i c t l y empirical and does not indicate why five membered ring formation should be preferred. An often used explanation for the direction of cycloaddition i s based on the supposition that i n i t i a l bond formation occurs in such a way as to produce the most stable diradical 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 in 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 79, 80, or 81 COOEt COOEt 82 - 85 Eq 81 H 103 (94 + 95) lOOEt :00Et 105 - 73 -factors which mitigate against this radical s t a b i l i t y argument. Recently, the importance of the stabilizing influence of the carbonyl group on an a radical (103) has been cast in doubt by the work of King, Golden, and 83 Benson. Thermal studies on the bromination of acetone indicate that there is no stabilization in the acetonyl radical (106). This indicates 0 0 II I CH 3-C-CH 2« CH3-C=CH2 106 107 that structure 107 does not contribute toward the s t a b i l i t y of 106. There is a stabilization energy of 2.7 kcal/mole in going from the acetonyl to the methyl acetonyl radical but this change i s in line with the stabilization 19 gained in going from a primary to a secondary radical. 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 diradicals 103, 104, and 105. Secondly, while a few photochemical cycloadditions (e.g., myrcene (Eq 29) and isogermacrone(Scheme 6)) proceed through the formation of their most stable diradical intermediates most cyclizations do not. This is especially so in the case of 1,5 dienes (Eq 82). hv 1 » \ / > / T \ Eq82 X = 0 or CH2 - 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 diradicals which do not d i f f e r significantly in s t a b i l i t y and yet in the case of cyclooctadiene only "crossed" cycloaddition occurs while "straight" cyclization occurs exclusively for cyclodeca-3,8-diene-l,6-dione. The above observations tend to rule out the v a l i d i t y of using radical s t a b i l i t y to explain the direction of cycloaddition in the photolyses of the geometric isomers of diethyl 2,8-decadiene-l,10-dioate Another possible explanation for the direction of i n i t i a l bond formation in 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 olefin. I n i t i a l excitation followed by d e r e a l i z a -tion produces an intermediate diradical species which possesses a radical 84 centre on (Eq 83 - 85) and a radical centre on the carbonyl oxygen. The radical centre at is now capable of adding intramolecularly to the ground state olefin. I n i t i a l bonding by the 3 carbon (C^) of a photochemically excited a,3-unsaturated carbonyl species has been recently (79 81). hv COOMe Eq 83 108 109 - 75 -Is^vrCOOMe 1 C^OOMe 96 hv •OMe a 1 \b I \ l \ 110 s^N^vCOOMe Eq 84 COOEt COOEt (79 - 81) hv 0 ^ ^ O E t 111 j \ b -COOEt Eq 85 85 established by the work of D i l l i n g on the mixed cycloaddition of cyclo-90 79 76 pentenone to 1,2-dichloroethylene. Experimentally, ' ' the radical centre on C^ in diradicals 109, 110, and 111 cyclize at the olefin centre via path b_ (five membered ring formation), path a_ (five membered ring formation), and path a_ (six membered ring formation) respectively. These cyclizations (i.e., via path a_ or b) can be compared to the ground state intramolecular addition of a free radical to an olefinic centre (Scheme 11). When n (the number of carbon atoms separating the free radical centre from the olefin centre in 112) is equal to 2, Julia states that there i s relatively poor overlap between the free radical centre and the olefin centre in both path a_ and path b_ cyclizations. Experimentally, this i s supported by the fact that cyclization of 87—89 4-pentenyl free radicals (n = 2) is only a minor reaction pathway 86 compared to competitive intermolecular reactions. When cyclization does - 76 -Scheme 11 (CH9) path a. (CH ) n \ \b \ \ \ 112 R„ ath b (CH 2) n (For X, Y, R , R2, and n-See Table 3) R-, 114 2 87 88 occur ' exclusive five membered ring formation (path b) is observed (Table 3). Classically, preferential path b_ cyclization can be ration-alized on the basis of the relative radical and thermodynamic s t a b i l i t i e s of the species involved in path a_ and path b_ cyclizations (Scheme 11). These results for 4-pentenyl free radicals closely parallel those of the photochemical intramolecular addition of 109 (Eq 83). Photochemically, 90 only five membered ring formation (i.e., "crossed" cycloaddition, path b) is observed. 86 89 When n = 4, molecular model investigations ' indicate good overlap of orbitals for path a_ and poor overlap for path b_. This indicates that six membered ring formation (path a) should be favored over seven membered ring formation (path b). Furthermore, thermodynamic s t a b i l i t y of the six membered ring and probability factors governing the cyclization - 77 -of the radical both tend to favor path a_. Experimentally, 6-heptenyl free radicals cyclize intramolecularly to give preferential ly six 86 89 membered ring formation (path a) . ' The photochemical analogue of this cycl izat ion ( i . e . , cycl izat ion of 111) gives products indicative 76 of an exclusive path a mechanism ("straight" cycloaddition). The cycl izat ion of 5-hexenyl free radicals (n = 3) does not present i simple a picture as when n = 2 or 4 (Table 3). Here molecular models Table 3_ n X Y *1 *2 Path a(%) Path b(%) R< 1 H H H H 0 0 88 2 H H • H H 0 14 88 2 CN COOEt H Me 0 30 87 2 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 0 86 86 89 indicate good overlap ' of the free radical with both centres of the o l e f i n moiety. Based on the thermodynamic s t a b i l i t i e s of the products formed (cyclohexane vs. methylcyclopentane) and on the radical s t a b i l i t i e s , of the intermediates (cyclohexyl radical vs . 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 -21 work of Brace on the treatment of 1,6-heptadiene with iodoperfluoro-propane (Rpl) leads exclusively to cyclopentane formation (Eq 86). He 89 offers no explanation for the generality of these reactions. Walling has found that the reaction between 5-hexenyl mercaptan and tr i e t h y l phosphite results in preferential methylcyclopentane formation (Eq 87). R FI CH2RF ^ C H 2 i Eq 86 + P(OEt). Eq 87 0% at 60° 3% at 120° 43% at 60° 50% at 120° di-t-butyl peroxide s 84% "Ph 8% Eq 88 Only when he raises the temperature of the reaction from 60° to 120° does he find any cyclohexane formation. He comments on the fact that there is l i t t l e difference in the steric requirement for closure at (path a_) or at Cg (path b) and indicates that formation of methylcyclopentane i s - 79 -probably kinetic in nature. Further evidence for this similiar, unique 88 behaviour of 5-hexenyl free radicals comes from the work of Pines on the treatment of l-phenyl-6-hexene with di-t-butylperoxide. Here (Eq 88) some cyclohexane formation occurs but i t is very minor compared to the amount of methylcyclopentane formed. If, as indicated in the above examples (Eq 86 - 88), the free radical cyclizes kinetically then the formation of the cyclohexyl and the cyclopentylmethyl radical must be irreversible. This has been shown to be true as the thermal decomposition of di(cyclohexyl-formyl) peroxide and di(cyclopentyl-acetyl) peroxide 23 give only cyclohexane and methyl cyclopentane respectively. There are several examples, when the free radical i s highly stabilized, that six 22 86 91 membered ring formation i s preferred (Scheme 12). ' ' These results 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 reversible formation of the cyclohexenyl and cyclopentylmethyl radicals, followed by irreversible 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 kinetic control when the free radical i s stabilized. In order to support his scheme for the reversible path a_ and path b_ cyclizations (Scheme 12), J u l i a thermolysed the appropriately substituted (R^ = CN and = COOEt - Scheme 12) tertiary-butyl cyclohexyl performate and tertiary-butyl cyclopentyl peracetate, and found that they both gave mixtures of cyclohexane and methyl cyclopentane products. The similarity between the cyclization of 5-hexenyl free radicals and photocyclization of the 1,6 dienes 96_ probably l i e s in the kinetic closure to form a five membered ring via path a_. It has been 18 shown by Liu and Hammond that their intermediate diradical (11) is formed irreversibly. There is no reason to expect that the cyclization of 110 (Eq 84) would be reversible. Experimentally 110 (photochemically excited 96) cyclizes exclusively via path a_ to form "straight" addition j . 79 products. It can be concluded that both ground state and photochemical intra-molecular cyclizations of alkenyl free radicals 112 (n = 2 and 4) proceed in a manner expected on the basis of the radical and thermodynamic s t a b i l i t i e s of the species involved. However, five membered ring formation in the cyclization of 5-hexenyl free radicals (n = 3, 112) and in the analogous photochemical cyclizations (Eq 84) is proceeding via a kinetic 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 direction of i n i t i a l bond formation in photochemical cycloadditions is based on the possibility that the f i r s t step i s controlled by the symmetry of the highest occupied 2 2 molecular orbital. If a n + TT geometry of approach of the olefins i s s s assumed then the mixing of their bonding (TT^ ± T T^) and antibonding ( i r ^ * ± T^*) orbitals (Fig 5) w i l l produce a set of four new non-degenerate molecular orbitals. If excitation occurs, the highest occupied molecular orbital (ijO predicts that the f i r s t step should proceed in a "straight" manner. Such a molecular orbital approach explains the direction of cycloaddition in 1,4- 1,6- and 1,7- dienes but f a i l s to explain "crossed" cycloaddition in 1,5 dienes (Eq 89 ). If the orbitals of the 3,4 sigma bond in 1,5 dienes were mixed with the four molecular orbitals ty - ty. - 82 -Eq 89 derived above then a possible crossing of the energy levels of ty^ and IJ^  and and may occur. Cookson (See Introduction) has done a similar mixing of the central sigma bond in order to explain the Cope rearrange-35 ment of 1,5 dienes. If the mixing of the sigma bond is sufficiently large and level changing does occur then the highest occupied molecular orbital i n the excited state is \p. (See Fig 3) and this 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 has published a paper dealing with this topic speci f i c a l l y . The application of through-bond coupling to 1,5 dienes, however, i s very speculative and many factors such as different geometries of approach in the transition state, non-coplanarity of the sigma and pi systems and steric interactions probably render such an explanation inconclusive. It i s hoped that future studies in photoelectron - 83 -spectroscopy w i l l be able to determine the extent of through-bond interactions on the direction of photocycloaddition of 1,5 dienes. (4) Direct Irradiation of Compounds 79, 80, and 115 a) Photolysis of 79 Photolysis of _79 in either methanol or hexane under Corex optics led to a complex mixture of photoproducts 19_, 8>0, {51_, 115, 116, and 117. Continued irradiation led exclusively to the formation of 117. As indicated by analytical vpc, photoproducts jK), 81_, 115, and 116 build up i n i t i a l l y and then disappear in 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 for the formation of 117 and a less obvious one for 115 and 116. - 84 -b) Characterization of Photoproducts 79 - 81 and 115 - 117 Characterization of the photoproducts was made on the basis of their nmr and i r spectra as given in Table 4. The geometries of the various double bonds were indicated by characteristic 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 (cis 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 ester). Furthermore the geometry of the double Table 4 Compound Double Bond Position and Geometry CH=CH Coupling Constants (Hz) IR Double Bond C-H Rock (y) IR C=( 79 trans -a ,3 15.5 10.15 5.81 trans-a,g 15.5 10.15 5.81 80 trans-a,3 15.5 10.04 5.81 cis - a , 3 11.5 11.97 5.81 81 cis - a , 8 11.6 12.04 5.82 cis - a , 3 11.6 12.04 5.82 115 trans -a ,3 15.4 10.18 5.82 trans-3,y mult 10.18 5.79 116 cis - a , 3 11.5 11.93 5.83 trans-3,y mult 10.14 5.79 117 trans-3,y mult 10.27 5.74 trans-3,Y mult 10.27 5.74 bonds in the case of the a,3-unsaturated esters was indicated clearly by nmr. The 3 proton always appeared as a doublet of tr i p l e t s with a coupling - 85 -constant of 15.5 Hz (trans double bond) or 11.5 Hz (cis double bond). The a vinyl hydrogen appeared as a doublet with small a l l y l i c (1.5 Hz) coupling The vinyl hydrogens of the B,Y_unsaturated double bonds were complex multiplets and a shift reagent was used in order to determine the geometry 93 of the double bonds in 117. The use of tris(dipivalomethanato)europium in a CCl^ solution of 117 caused the equivalent and Cg vinyl hydrogens to appear as two distinct triplets with a typical trans vinyl coupling constant of 15.7 Hz. This value could also be obtained from the broad doublet responsible for the C^ and C^ vinyl hydrogens. These assignments were supported by decoupling experiments (See Experimental). Further proof of structure for photoproduct J50 came from an independent synthesis 7"* while the structure of 117 was verified 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. Chiusoli for a generous sample of trans,trans-deca -3 ,8-diene-l,10-dicarboxylic acid. Finally, analytical analyses were obtained on the unknown compounds 81, 115, and 116 which supported their isomeric structures. Mass spectral fragmentation patterns of the photoproducts are in agreement with the structures presented in Scheme 13. c) The Photolysis of 80 and 115 Scheme 13 was further supported by the direct photolysis of 8_0 and 115. Diene-diester 80_ led to photoproducts 81, 115, 116, and 117 with 117 being the sole product after extended irradiation. At no time was the appearance of 79 observed. On photolysis, trans,trans-diester 115 i n i t i a l l y gave compound 116, and after an observable induction period, compound 117. - 86 -Compound 117 was the only product after continued photolysis. At no time in the photolysis of 115 were compounds 7_9 - 8JL observed. d_) Quenching Studies Photolysis of 79_ (0.001 moles) in hexane in the presence of varying amounts of piperylene (0.005 moles, 0.05 moles, and 0.2 moles) led to a mixture of products in accord with Scheme 13. The time for the photolyses was, however, greatly affected. The larger the amount of piperylene present the longer i t took for deconjugation to occur. (5) Discussion of the Direct Irradiation of Compounds 79, 80, and 115 Photodeconjugation of an a,6-unsaturated ester to the corresponding $,Y -unsaturated ester is a f a i r l y well documented reaction (See Introduction). The most generally accepted mechanism involves trans to cis isomerization followed by y hydrogen abstraction by the n ,ir* excited singlet state of the ester carbonyl. The resulting diradical forms a dienol which can ketonize to give the observed 3>Y isomer. The intermediacy of the cis olefin in the photodeconjugation of 79 i s , in general, indicated by Scheme 13 and in particular, by the photolysis of 115. Direct irradiation of 115 gives at f i r s t 116 and then after an induction period deconjugated product 117. These results indicate that the cis (a,6),trans (3,Y) isomer 116 and not the trans (a,3),trans (3,Y) isomer 115 i s the immediate precursor of 117. The excited state responsible for the deconjugation observed in the irradiation of 79, 80, 62 6A and 115 is the n ,Tr* singlet state. ' The assignment of the excited state is supported by photolysis experiments under Corex optics where - 87 -only the n , T r * absorption band of the a,3-unsaturated ester i s absorbing 76 light. The multiplicity i s supported by the sensitization and quenching studies. Triplet sensitization failed to give any deconjugation. Under these conditions only cycloadded product formation was observed. Quenching experiments with piperylene failed to prevent photodeconjugation from occurring. With larger amounts of piperylene present the rate of the deconjugation was slower but this could be due to a slower rate of trans to cis isomerization. The rate of photodeconjugation i s faster than cis to trans isomerization as no 79_ is observed in the direct irradiation of 80. Unique to this system i s the fact that only the di-3,y-trans,trans isomer 117 is formed in the deconjugation of 79, 80, and 115. Other authors have found a much less preference for the formation of the trans 3,y 59 isomer (See Introduction). These results may be explained by the mechanism presented in Scheme 14. Trans to cis 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-orbital on oxygen in the n ,Tr* singlet state (118) leads i n i t i a l l y to a species 119. This could then undergo rotation about the 3,Y~carbon carbon bond to give either the cis (120) or the trans (121) dienol. The latter would be the most favored on steric grounds. This is supported experimentally as only the trans deconjugated product is observed. These results 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 specified chain length and known geometry can be prepared in this manner. (6) Conclusion Like 3,y-unsaturated ketones, the photolysis of acyclic 1,7 diene-diesters (79, 80, and 81) show unique properties under direct and sensitized conditions. In the presence of t r i p l e t sensitizers 1,7-dienes cycloadd i n a "straight" manner to give a mixture of cis and trans fused bicyclo[4.2.0]octanes. Under direct irradiation, photodeconjugation occurs to give exclusively the trans,trans isomer 117. - 89 -C.) Cyclonona-2 ,6-dienone A literature survey of the photochemistry of cyclic non-conjugated dienes (See Introduction) quickly demonstrates the tendency of the dienes to give cycloaddition products indicative of i n i t i a l five-membered ring formation. 1,5-Cyclooctadiene (Scheme 2) and isogermacrone (Scheme 6) are typical examples of 1,5- and 1,6 dienes respectively, which photochemically cycloadd in this manner. Perhaps due to synthetic d i f f i c u l t i e s , homologous cyclic 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. ' Of these cyclic dienes, 1,5-cyclononadiene (122) possesses the unique property of being able to photochemically cycloadd via i n i t i a l five-membered ring formation to give both "straight" and "crossed" addition products (Scheme 15). Scheme 15 H H 122 or I I Straight I I it Crossed I I - 90 -The photochemistry of 122 could shed some light on the mechanism of cycloaddition in non-conjugated dienes depending on whether "straight" or "crossed" product formation predominated. Based on this unusual property of cyclononadiene i t was decided that such a skeleton would become the basis of a photochemical investigation. Compound 122 is in i t s e l f a poor choice for such an investigation as i t s ultraviolet absorption region i s not easily accessible by conventional light sources. It was decided then that 2-bromo-cyclonona-2,6-dienone (126), and cyclonona-2>6-dieneone (128) would make good starting materials. 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 easily accessible ultraviolet absorption region. Scheme 16 outlines the synthetic approach taken to obtain ketones 126 and 128. Cyclooctadiene was converted to 9,9-dibromo-bicyclo-9 9 [6.1.0]non-4-ene (123) by the method of SkattebAl. Compound 123 was then subjected to a Ag + assisted acetolysis by s t i r r i n g i t in a solution of silver acetate in acetic acid for two days. This results in the stereospecific^"^ formation of 2-bromo-3-acetoxy-cis,trans-cyclonona-1,6-diene (124) This was easily converted to the alcohol (125) by alkaline hydrolysis of the acetoxy group. Many attempts to oxidize alcohol 125 -,u • -A- • «. / T 1 0 2 i , 103 _ ... 104 with various oxidizing reagents (e.g., Jones, Browns, Collins Comforth,^^ AgO, and Mn02^^) to the corresponding ketone proved f r u i t l e s s . Equimolar mixtures of oxidizing reagent and alcohol usually returned starting material unreacted, while excesses of reagents produced inseparable complex mixtures of products. The failure of the oxidation of 125 could be due to the influence of the bromine group. In order to test this hypothesis the removal of the bromine was carried out by sti r r i n g alcohol 125 in an excess of sodium in liquid a m m o n i a . T h i s gave in good yield trans,cis-2,6-dienol (127). Several attempts (MnO^, Browns oxidation, and Collins oxidation) at oxidizing 127 to the correspond-ing ketone also failed. Some encouraging results have been obtained with the use of Jones reagent although the yield of product suspected to be ketone 128 is quite low (<10%). Work at characterizing this product and at improving i t s yield is presently underway. - 92 -EXPERIMENTAL A) General Procedures Infrared (ir) spectra were obtained, unless otherwise stated, on neat liquid 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. In a l l cases tetramethylsilane was used as an internal standard. Mass spectra were obtained on a direct inlet AEI MS-9 instrument at 70 eV, and ultraviolet spectra were recorded on a Unicam SP-820 spectrophotometer. Melting points were taken on either a Thomas-Hoover (TH) capillary apparatus or a Fisher-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 strip chart recorders. The carrier gas in a l l cases was helium. The following analytical (A -5' x 1/4") and preparative (P - 20' x 3/8") columns were used: 20% SE-30 on 60/80 Chromosorb W A/W DMCS, (column A - l ) ; 20% DEGS 60/80 Chromosorb W, (column A-2); 10% Carbowax 60/80 Chromosorb W, (column A-3); 10% FFAP 60/80 Chromosorb W, (column A-4); 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 in parenthesis after the column stated. - 93 -Thin layer chromotography (tic) was carried out on plates coated with E. Merck and Co. S i l i c a Gel G. Grace (activated) S i l i c a Gel was used for column chromotography. Large scale photolyses (internal) were carried out in a water-cooled Quartz immersion well apparatus. Small scale photolyses (external) were performed by placing the solution to be photolysed in a 50 ml Quartz tube and strapping this to the outside of the water-cooled immersion well. 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 solution of sodium methoxide and dimethyl phthalate.^ A l l organic reagents used were reagent grade unless otherwise indicated. Photolysis solutions were degassed prior to irradiation with Canadian Liquid Air 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 latter case, i t was necessary to isolate germacrone from Zdravetz o i l . The contents from a one ounce bottle of zdravetz o i l were f i l t e r e d to yield 2.2 g of crude yellow crystals, mp 50-53" uncor. One recrystallization from methanol (15 ml) yielded 1.9 g of needle-like white crystals of 68, mp 55 —55.5 uncor ( l i t . ^ ^ 55.5°-56°). A small amount of triacontaine,^ mp 66° was present as an impurity and could be effectively removed by elution on S i l i c a Gel with hexane. Germacrone isolated in this manner had the following spectral characteristics: uv max (MeOH) 246 nm; i r (CHC1,) - 94 -5.97 (C=0), and sh 6.02 (C=C) u; nmr (CC1.) T 4.45-5.00 (m, 2, C. and C 0 v i n y l H), 6.55-7.33 (m, 4, C 2 and C g CH 2), 7.88 (broad s, 4, C 5 and C g CH2>, 8.23 (s, 3, C 1 4 CH 3), 8.30 (s, 3, C 1 5 CH 3), 8.42 (s, 3, C CHg), and 8.60 (s, 3, C^2 CH ) . These spectra are in f u l l agreement with those reported by V. G. Oh l o f f . 6 6 Synthesis of Isogermacrone. A solution of germacrone (1.92 g, 0.0088 mole) in 50 ml of ethanolic 0.5 N potassium hydroxide was refluxed under nitrogen for 4 hrs. After this period, t i c (10% ether-benzene) indicated the presence of starting material and one new product; the latter being the most intense spot under iodine development. The solvent was removed in 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 sulfate). The chloroform was removed in vacuo to yield 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. Purification 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). Crystallization of the clear o i l , obtained from column chromatography, from methanol gave white crystals, mp 48°-50° uncor ( l i t . ^ 51°-52°). Isogermacrone exhibited the following spectral characteristics: uv max (hexane) 203, 252, and 330 nm; i r (CHC13) 6.00 (C=0), and 6.14 (C=C) u; nmr (CDC13) x 3.99 (s, 1, C 2 v i n y l H), 4.82 (t, 1, Cg vinyl H), 6.82-7.20 (m, 2, C g CH 2), 7.40-8.60 - 95 -(m, 6, C 4, C 5, and C g CH2) , 8.19 (d, 3, CHg) , 8.32 (m, 6, C and C15 C H3^' a n d 8 " ^ 8 3> C i 2 C H3^* T n e s e spectral characteristics are 66 in f u l l agreement with those previously reported for isogermacrone. Photolysis of Isogermacrone (69). A solution of 69_ (0.454 g, 0.00208 mole) in 500 ml of benzene was photolysed internally through a Pyrex f i l t e r for 55 min. Tic (10% ether-benzene) indicated the disappearance of starting material. Removal of the benzene in 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): A, 2.9 min, 1.00; B_, 13.4 min, 9.07; C_, 58.3 min, 4.86; D, 79.5 min, 96.8; E_, 86 min, 59.0; F, 96 min, 10.47; G, 122 min, 18.81. Retention times were taken relative to the air peak. The major products at retention times 79.5 min (70, D) and 86 min (71, E) accounted for 78% of the total product mixture. Nmr (CDCl^) of this crude mixture indicated the absence of vinyl hydrogens. Isolation of Photoproducts 70 and 71. The above photomixture was subjected to preparative vpc column P-l (200°, 60 ml/min). Photoproducts 70_ and 71 were collected in this manner and found to be colorless liquids. Photoproduct 70 exhibited the following spectral characteristics: i r (CHC13) 5.88 (C=0), and 6.14 (C=C) y; nmr (CDC13) T 7.25-7.61 (broad m, 4), 7.78 (broad t, 3), 8.17 (broad s, 3), 7.92-9.0 (broad m, 6) 8.81 (s, 3, C 7-CH 3), and 8.92 (s, 3, C^-CH^); mass spectrum (70 eV) m/e (rel intensity) 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 for C^H^O: C, 82,51; H, 10.16. Found: C, 82.39; H, 10.21. Photoproduct 7_1 had the following spectral properties: i r (CHCl^) 5.88 (C=0), and 6.13 (C=C) y; nmr CCDC13) x 7.18-7.97 (broad m, 6), 7.97-9.0 (broad m, 7), 8.12 (broad s, 3), 9.10 (s, 3, C ?-CH 3), 9.17 (s, 3, C^-CR"3) ; mass spectrum (70 eV) m/e (rel intensity) 218(12), 123(21), 122(52), 96(99), 95(80), 91(20), 81(100), 79(24), 77(20), 68(14), and 67(17). Anal. Calcd for C^H^O: C, 82.51; H, 10.16. Found: C, 82.31; H, 9.98. Isolation of Photoproducts F and G. Although present i n small amounts, sufficient quantities of F_ and G_ needed for crude spectral analyses were obtained by preparative vpc (column P - l , 200°, 60 ml/min) separation of an isogermacrone photolysis mixture. Photoproduct 1? collected i n this manner gave the following spectral characteristics: i r (CHC13) 5.95 (C=0), and 6.16 (C=C) y; nmr (CDC13) x 7.00-9.30 (featureless broad multiplet with large multiplet centres at x 7.80(1), 8.25(3) and 8.90(2). Photoproduct (2 collected under identical conditions showed the following spectral properties: i r (CHC13) 5.90 (C=0), 6.13 (C=C) y; nmr (CDC13) x 6.6-9.4 (broad multiplet with broad singlets centred at x 7.80(2), 8.17(2), 8.27(2), 9.13(1) and 9.25(1); mass spectrum (70 eV) m/e (rel intensity) 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) in 15 ml ethyl acetate was hydrogenated over 8 mg of Adams Catalyst for 5 hrs. F i l t r a t i o n through Celite and removal of solvent in vacuo afforded 0.154 g of clear o i l . Vpc column A-4 (165°, 60 ml/min) indicated that the product was 90% pure. This was further purified by collection on the same column. Hydrogenated 13 gave the following spectral characteristics: i r (CHCl^) 5.82 (C=0) y; nmr (CDC13) T 7.3-8.65 (featureless broad m, 10), 8.65-9.3 (featureless multiplet, 14); mass spectrum (70 eV) m/e (rel intensity) 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 for C^H^O: C, 81.73; H, 11.00. Found: C, 81.36; H, 11.18. In an analogous manner 71_ (50 mg, 0.227 mmoles) was hydrogenated to give 40 mg of crude product. Vpc column A-1 indicated that at least 80% of the mixture was one product. The following spectral characteristics were taken on this crude mixture: i r (CHCl^) 5.82 (C=0) y; mass spectrum (purified by vpc collection) (70 eV) m/e (rel intensity) 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 anti (74) 1,7-Dimethyltricyclo decane-97 3-one. A solution of 1,2-dimethyl cyclopentene (Chemical Samples, 99% pure) (22.43 g, 0.233 mole) in absolute ether (175 ml) was photolysed through Corex for 8 hours. Cyclopentenone (Aldrich Chemical Co.) (13.00 g, 0.158 mole) was added dropwise to this 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 starting materials were removed in vacuo to give 15.92 g of a yellow-orange liquid. According to column A-1, 57% of the crude product mixture was _73 and 74 i n a 5:3 ratio respectively. The two desired products were isolated and purified by preparative vpc column P-3 (210°, 60 ml/min). The following spectral properties were obtained for 73_: i r (CHCl^) 5.83 (C=0) u ; nmr (CDC13) x 6.33 (s, 1, C 2 CH), 7.30-9.00 (broad m, 11, C 4, C 5, Cg, C g, C 1 0 CH2 and C g CH), 8.85 (s, 3, C 1 2~CH 3), and 8.93 (s, 3, C^^-CH3); mass spectrum (70 eV) m/e (rel intensity) 178(24), 121(30), 109(26), 107(30), 96(65), 95(36), 93(38), 91(37), 81(100), and 79(40). Anal. Calcd for C^H^O: C, 80.81; H, 10.12. Found: C, 80.84; H, 10.25. Photoproduct _7_4 exhibited the following spectral properties: i r (CHC13) 5.83 (C=0) y; nmr (CDC13) x 6.38 (s, 1, C 2 CH), 7.45-8.05 (m, 5, C 4, C 5 CH2 and C & CH), 8.05-8.80 (m, 6, C g, C g and C 1 Q CH 2), 8.99 (s, 3, C 1 2-CH 3), and 9.11 (s, 3, C^-CH^ ; mass spectrum (70 eV) m/e (rel intensity) 178(24), 136(20), 121(20), 107(18), 96(72), 95(27), 93(20), 81(100), and 79(24). Anal. Calcd for C 1 0H 1 00: C, 80.81; H, 10.12. Found: C, 80.59; H, 9.99. 2 6 Condensation of syn-1,7-Dimethyltricyco[ ' ]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) in absolute ethanol (15 ml) was refluxed under nitrogen with sti r r i n g - 99 -f o r f o u r h r s . A f t e r t h i s p e r i o d , t i c (10% ether-benzene) i n d i c a t e d the disappearance of s t a r t i n g m a t e r i a l and the formation of a s i n g l e product. 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 a c i d . The ethanol was removed i n vacuo and the residue was taken up i n 10 ml of ether and 10 ml of water. The l a y e r s were separated and the aqueous l a y e r was e x t r a c t e d w i t h ether (1 x 10 m l ) . The ether e x t r a c t s were combined, washed w i t h water (1 x 10 m l ) , and d r i e d (Na2S0^). The ether was removed i n vacuo to y i e l d 0.095 g of y e l l o w o i l . Vpc column A-3 (170°, 40 ml/min) i n d i c a t e d that 95% of t h i s o i l was compound 70. 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_ which was i d e n t i c a l (nmr, i r , mass spectrum) to 7_0 obtained i n the p h o t o l y s i s of isogermacrone. 2 6 72 Condensation 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 ' ]decane-3-one (74) w i t h Acetone. In a s i m i l a r manner 74_ (0.131 g, 0.00074 mole) was 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 metal (0.0856 g, 0.00372 mole). Workup i n the u s u a l manner y i e l d e d 0.170 g of y e l l o w o i l . Vpc column A-3 (170°, 40 ml/min) i n d i c a t e d that 88% of the o i l was compound 71. P u r i f i c a t i o n by vpc y i e l d e d pure 71^ which 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 "photolysis of isogermacrone. C) ACYCLIC DIENE-DIESTER 74 75 P r e p a r a t i o n of D i e t h y l trans,trans-deca-2,8-diene-l,10-dioate. * A mixture of 1,10-decanedioic a c i d (Eastman Organic Chemicals, 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 three-necked 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° for 2 hrs. Heating was discontinued, and bromine (AnalaR) (229 g, 1.43 mole) was added 74 dropwise to the clear yellow solution. During the addition the complete apparatus was irradiated with a 275W sun lamp. After the addition was complete (1 hr), the dark brown solution was heated in the dark between 90 and 100° for 5 hrs. The solution was then cooled to 0° and absolute ethanol (165 ml) was added dropwise followed by a solution of sodium bicarbonate (25.84 g } 0.308 mole) in 205 ml of water. Chloroform (200 ml) was added and the two layers were separated. 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 solution (2 x 200 ml), decolorized (Norit), and dried (MgSO^). The chloroform was removed i n vacuo to yield 210 g of a light yellow liquid. The following spectral data confirmed this liquid to be diethyl-2,8-dibromodecane-l,10-dioate: i r (neat) 5.78 (C=0) u; nmr (CC14) x 5.78 (q, 4, C00CH_2CH3) , 4.00 (t, 2, J 2 3 = 7.2 Hz, CHBr-COOEt), 8.00 (m, 4, CHoCHBr-C00Et), and 8.70 (m, 8, C., C c, C,, — —Z H J O and Cj CH 2). The crude yellow o i l (210 g, 0.504 mole) was refluxed in dimethyl formamide (420 ml) for 4 h r s . 7 5 The solution was cooled and to i t were added 800 ml of water and 300 ml of ether. The mixture was then separated. 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 in vacuo to give 124 g (97%) of an orange li 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 ci s , trans isomer J50. D i s t i l l a t i o n through a Vigreux column resulted in a colorless l i q u i d , bp 104° at 0.02 mm (reported7"* bp 127° at 0.28 mm). 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 in this manner showed the following spectral 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> J 2 3 = J8 9 = 15.5 Hz, J_ . = J , 0 = 6.8 Hz, trans CH=CH-C00Et) , 4.22 (d, 2, J„ = J Q _ = 15.5 Hz, trans CH=CH-C00Et), 5.85 (q, 4, C00CH_CH_), 7.78 o, y — —z j (broad d, 4, J_ . = J., Q = 6.8 Hz, C. and C, CH0) , 8.50 (m, 4, C,. and C 6 CH 2), and 8.73 (t, 6, C00CH2CH3); mass spectrum (70 eV) m/e (rel intensity) 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,10- dioate (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 irradiated through Vycor and the course of the reaction followed by analytical vapour phase chromatography using column A-2 (170°, 120 ml/min). Five new peaks in addition to starting material were observed corresponding to photoproducts 80, 81, 115, 116 and 117 the 98 latter being the ultimate sole product after 2.5 hrs of irradiation. 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 -Isolation and Identification of Photoproducts 80, 81, 115, 116,  and 117. Irradiation as above for 90 min led to near-maximum amounts of photoproducts 80_, 8^, 115 and 116. These products were separated and isolated by vpc column P-2 ( 1 7 5 ° , 200 ml/min). Photoisomer 117, was isolated 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 colorless l i q u i d s . The structure of 80_ was deduced to be diethyl cis,trans^-deca-2,8-diene-1,10-dioate from the following data: 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 0 _ » 15.5 Hz, J , 0 = H o, y / , o 6.8 Hz, trans CH=CH-C00Et), 3.92 (d of t , 1, J = 11.5 Hz, J_ , = 7.3 Hz, cis CH=CH-C00Et), 4.32 Cd, 1, J g g = 15.5 Hz, trans CH=CH-C00Et), 4.36 (d, 1, J 2 3 = 11.5 Hz, cis 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 ? CH2) , 8.52 (m, 4, C 5 and C g CH2) , and 8.76 (t, 6, COOCH2CH_3); mass spectrum parent (70 eV) m/e 254. Photoproduct 1_ was identical to an independently prepared sample of diethyl cis , trans-deca-2,8-diene-1 ,10-dioate . 7 5 Photoisomer J31_ was shown to be diethyl cis ,cis-deca-2 ,8-diene-1,10-dioate from the following: i r (neat) 5.82 (C=0), 6.07, and 12.04 y; nmr (CC1.) x3.91 (d of t, 2, J_ „ = J . n = 11.6 Hz, J . . = J , - = 7.3 Hz, ^ Z , J o,y J,4 / ,o cis CH=CH-C00Et), 4.38 (d, 2, J = J = 11.6 Hz, cis CH=CH-C00Et), z, J o, y 5.95 (q, 4, C00CH CH.) , 7.37 (broad d, 4, J . . = 0 = 7.3 Hz, C. and C ? CH 2 ) , 8.53 (m, 4, C 5 and C& CH2) , and 8.78 (t, 6, C00CH2CH_3) ; mass spectrum (70 eV) m/e (rel intensity) 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 for C 1 4 H 2 2 ° 4 : C» 6 6' 1 2'* H ' 8 , 7 2 # F o u n d : c» 65.94; H, 8.59. Photoisomer 115 was shown to have the structure diethyl trans,trans-deca-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 (CC14) x 3.18 (d of t, 1, J Q n = 15.4 Hz, J., _ = 6.8 Hz, trans CH=CH-C00Et), 4.32 (d, 1, J Q _ = o,y /,o — o,y 15.4 Hz, trans CH=CH-C00Et), 4.50 (m, 2, CH=CH), 5.90 (q, 2, COOCH^CH^, 5.92 (q, 2, C00CH2CH3), 7.07 (m, 2, C 2 CH2) , 7.85 (m, 4, C 5 and C y CH 2), 8.38 (m, 2, C g CH 2), and 8.70 (t, 6, C00CH2CH_3) ; mass spectrum (70 eV) m/e (rel intensity) 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 for C..Ho,,0. : C, 66.12; H, 8.72. Found: C, 65.94; 14 22 4 H, 8.80. Photoproduct 116 was proved to be diethyl deca-trans-3-cis-8-diene-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 g g = 11.5 Hz, J ? g = 7.2 Hz, cis CH=CH-C00Et), 4.37 (d, 1, J g g = 11.5 Hz, cis 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-, Q = 7.2 Hz, — Z J L i . I , O C-, CH„), 7.93 (m, 2, C c CH.) , 8.43 (m, 2, Z, CH0) , 8.75 and 8.78 (t, 6, / Z _> Z D z C00CH2CH_3) ; mass spectrum parent (70 eV) m/e 254. Anal.Calcd for C^H^O^: C, 66.12; H, 8.72. Found: C, 66.14; H, 8.55. Compound 117 was identified as diethyl trans,trans-deca-3,7-diene-I, 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_2CH3) , 6.97 (m, 4, C 2 and C g CH2) , 7.87 (broad s, 4, C 5 and C & CH2) , and 8.73 (t, 6, COOC^CH^) , mass spectrum (70 eV) m/e (rel intensity) 254 ( 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), 79 ( 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)3 showed the following signals attributable to the vinyl hydrogens at C 3 and C g: T 3.30 (d of t, 2, J 3 ^  = J 7 g = 15.7 Hz, J2 3 = J8 9 = 6 , 8 H z ' t r a n s CH=CH-CH 2-C00Et). The and vinyls appeared as: T 3.68 (broad d, 2, J „ . = 0 = 15.7 Hz, trans 3,h /,» CH=CH-CH 2-C00Et). Irradiation at C 2 and C g caused the C 3 and C g vinyl hydrogens to appear as a doublet, J = 15.5 Hz. Irradiation at C,. and Cg caused sharpening of the C^ and C^ doublet. A 60% aqueous dioxane solution of 117 (150 mg) containing 0.3 ml of cone HCl was refluxed under nitrogen for 22 hrs. Removal of the solvent i n vacuo afforded a wet white solid residue which was recrystallized from water, f i l t e r e d , and dried over R2^5 i n vacuo to yield 35 mg of yellow crystals. Norit decolorization followed by a further recrystallization from water afforded 25 mg of pure trans,trans-deca-3,7-diene-l ,10-dioic acid, mp 118 ° - 1 2 0 ° ( l i t . 9 5 118 ° - 1 2 0 ° ) . i r (KBr) 3.56 (OH), 5.91 (C=0), and 10.37 y; nmr (DMSO d &) T 4.47 (m, 4, CH=CH), 7.03 (m, 4, C 2 and C g CT^), and 7.90 (s, 4, C 5 and Cg C H 2 ) • This material was identical (mixed mp, i r , and nmr) to an authentic sample. 9 5 - 105 -Anal. Calcd for 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,10-dioate (80). Compound J50 (211 mg) in 200 ml of hexane was irradiated 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 attributable to photoproducts 81, 115, and 116 grew and then diminished while the peak due to j$0 steadily decreased and that due to 117 steadily increased. After 98 30 min, 117 was the only product detectable by vpc. A peak corresponding to _79_ was not observed at any time during the photolysis. A preparative vpc-collected (column P-l, 200°, 60 ml/min) sample of 117 from this run was identical to previous samples. Direct Photolysis of Diethyl trans,trans-deca-3,8-diene-l,10- dioate (115). 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 of 115 and the appearance of 116 was observed. At this point a peak corresponding to 117 appeared, u n t i l after 2.15 hrs there were approximately equal amounts of 115, 116 and 117. After 3.6 hrs, 117 was the sole product (> 95%) detectable by vpc. At no point during the photolysis were peaks corresponding to isomers 79, 80 or observed. A sample of 117 from this run, collected by preparative vpc (column P-l, 200°, 60 ml/min) was identical to previous samples. Acetone-Sensitized Photolysis of Diethyl trans,trans-deca-2,8- diene-1,10-dioate (79). Diene-diester 79 (1.27 g, 5 mmole) in 400 ml of acetone was irradiated through Corex (X > 260 nm) and the course of the - 106 -reaction followed by analytical vpc using column A-2 (170°, 120 ml/min). The percentage of the incident irradiation absorbed by the acetone at various wavelengths was calculated using the relation: % light absorbed by sensitizer = C c e c/C Q E„ + C e in which S refers to the sensitizer (acetone), D is the substrate being sensitized (diene-diester), C is the molar concentration, and e is the extinction coefficient at the wavelength in question. The calculated percentages are as follows (wavelength, %) : 255 nm, 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 in the ratio of 3.8 : 3.5 : 1.0. These products were isolated by column P-2 (170°, 200 ml/min) and identified by i r , nmr, and vpc retention time. In a separate experiment, 0.51'g (2 mmole) of 79^  in 500 ml of acetone was irradiated 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 hrs). The 79 : 80 : 81^ ratio remained constant at 3.8 : 3.5 : 1.0 during the transformation into cyclized products 82_ - 85. Compounds J32_ - J55_ had the following retention times on column A-2 (150°, 200 ml/min): 11.8 min, 82; 15.1 min, 83; 16.2 min, 85; and 19.7 min, 84. The products were formed in the following relative amounts (average of three runs): 82 (42%), 83 (15%), 84 (36%), and 85_ (7%); further irradiation led to loss of yield and eventual loss of any isolable products. Isolation and Identification of Cyclized Products 82 - 85. The crude photolysate from above (525 mg) was subjected to preparative vpc on column P-2 (165°, 200 ml/min) and the isolated products 82_ - 85_ further purified by Kugelrohr d i s t i l l a t i o n ; a l l were colorless liquids. On - 107 -larger scale photolyses the crude photolysate was i n i t i a l l y purified by elution on s i l i c a gel with 10% ether-benzene. This effectively removed any acetone by-products and any polymers which may have formed. The purified photolysate was then subjected to vpc separation as described above. Photoproduct 82 had the following spectral characteristics: i r (neat) 5.97 (C=0) u ; nmr (CC14) x 5.88 (q, 4, COOCH^CR^), 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_ (rel 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 CH2) , and 8.70 (t, 6, COOCH2CH_3) ; mass spectrum (70 eV) m/e ( r e l 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 characteristics: i r (neat) 5.78 (C=0) y; nmr (CC14) x 5.95 (q, 4, COOCH2CH3), 7.05 (m, 2, CH-COOEt), 7.34 (m, 2, CH-CH-COOEt), 8.52 (m, 8, cyclohexane ring CH 2), and 8.80 (t, 6, COOCH2CH_3) ; mass spectrum (70 eV) m/e (rel intensity) 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 their similar vpc retention times. Spectra of 85_ slig h t l y contaminated with 8^3 were in accord with the structure proposed: i r (neat) 5.80 (C=0) u ; nmr (CC±4) T 5.90 (q, 2, COOCH^CH^), 5.93 (q, 2, C00CH_2CH3), 6.40-9.00 (m, 12, CH-CH-(CH2)4-CH-CH) , 8.72 and 8.73 (t, 6, C00CH2CH_3) ; mass spectrum (70 eV) m/e (rel intensity) 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 infra) to the more stable trans-fused isomer 82_ in direct analogy to results obtained 78 with the corresponding dimethyl esters. The structures of photoproducts J32_ - were proved by direct compar-ison (retention time, i r , and nmr) with authentic samples obtained by the photoaddition of diethyl maleate to cyclohexene. 7 7 A solution of diethyl maleate (26.6 g, 0.155 mole) in cyclohexene (200 ml, 162 g, 1.98 mole) was irradiated through Vycor for 9 hrs. Removal of the cyclohexene in 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 in retention times to J32_ - 85_ were collected. Three of these proved to be identical (retention times, i r , and nmr) to J32_, 8_3, and J34. The remaining compound corresponding in retention time to 85_ was found to be unsaturated. - 109 -Further evidence for the structures of j52_, 83_ and 8h_ came from their 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 solution was acidified (aqueous HC1) to litmus, cooled, and centrifuged. The white solid 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 recrystallized once from ethyl acetate-petroleum ether to give the pure diacid, mp 180°-182° ( l i t . 7 7 181°-182°); nmr (DMSO-dg) x 7.17 (m, 2, CH-C00H), 8.53 (m, 10, -CH-(CH2)4-CH). Similarly j$3 afforded, after two recrystallizations from 20% acetone-benzene, pure cis,trans-bicyclo[4.2.0]octane-7,8-dicarboxylic acid, mp 197°-198° ( l i t . 7 7 mp 199°-200°); nmr (acetone d g) x 6.70 (d, 2, 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-7,8-dicarboxylic acid. Three recrystallizations from ethyl acetate-petroleum ether gave a mp of 170°-172° ( l i t . 7 7 174°-176°); nmr (acetone dfi) x 6.87 (m, 2, CH-COOH), 7.30 (m, 2, CH-CH-COOH), and 8.43 (m, 8, cyclohexane ring CH 2). Acetone-Sensitized Photolysis of Diethyl-cis,trans-deca-2,8-diene- 1,10-dioate (80). Diene-diester 80 (0.16 g, 0.63 mmole) in 200 ml of acetone was irradiated 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 of cyclized products 82_ - 85_ in the following relative amounts: 82 (44%), 83 (18%), 84 (31%), and 85 (7%). These - 110 -photoproducts were identical in vpc retention times and spectral characteristics to those previously observed. Acetone-Sensitized Photolysis of Diethyl-cis,cis-deca-2,8-diene- 1,10-dioate (81). Diene-diester 81 (89 mg, 0.35 mmole) i n 50 ml of acetone was irradiated externally through Corex u n t i l only photoproducts 82 - 85_ were present (5.5 hrs). Removal of the acetone yielded 0.144 g of yellow o i l . The products were separated by preparative vpc column P-2 (170°, 150 ml/min) and were identical in 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 in the photolysis of 79_ and 80_, and the f i n a l 82_ - j35_ photostationary state mixture differed as follows: 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) in 200 ml of benzene were irradiated through Pyrex and the reaction followed carefully by column A-2 (168°, 200 ml/min). I n i t i a l l y the ratios of 79, 80, and j31_ were identical to those found in the acetone-sensitized photolysis of ]9_ and 80. After 24 hrs, only products 82_ - j$5_ remained in the following relative amounts (obtained from column P-2, 170°, 180 ml/min): 82 (45%), 83 (16%), 84 (31%), and 85 (8%). The photoproducts were identified by their vpc retention times and i r spectra which were identical to previously isolated samples. Benzophenone was also found to sensitize the cycloaddition, but because of i t s retention time, the ratios of 82 - 85_ could not be obtained. Naphthalene failed to sensitize the photocycloaddition. - I l l -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) in 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 removed in vacuo, water added, and the mixture acidified (aqueous HC1) to litmus. The aqueous layer was extracted with chloroform ( 5 x 2 ml). The combined chloroform extracts were washed with water ( 1 x 4 ml) and dried (MgSO^). The chloroform was removed in vacuo to yield 0.036 g of o i l . Analytical vpc column A-2 (168°, 200 ml/min) indicated the presence of three products in the ratio 87 : 10 : 3. The f i r s t of these was identical to starting material (vpc, i r , nmr), and the second was shown to be stereo-isomer 85_ by vpc retention time and i r . The third product, present in minute quantities, was not isolated. cis,anti,cis-Diester 84 (0.068 g, 0.28 mmole) under identical conditions gave 0.054 g of o i l . Column A-2 (168°, 200 ml/min) showed two products in an 86 : 14 ratio. 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 in retention times to j}2_, 83_, 84, and J35_ after being subjected to the basic conditions previously described. The ratios of 82 : 85 and j$3 : 814 were 90 : 10 and 85 : 15 respectively. Compounds 82 and 84_ prepared i n this manner had identical spectral 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 thermolysed to d i e s t e r 83. 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 was observed. This r a t i o c o n s i s t e d of 81% 83 and 19% 84_; the i d e n t i t y of both was a u t h e n t i c a t e d by vpc and i r . With the exception of two low r e t e n t i o n time products ( d i e t h y l maleate and cyclohexene on the b a s i s of r e t e n t i o n times, sum < 1%), these were the only two products 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 mixture 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 to give the same products as i n i t s base-catalyzed e p i m e r i z a t i o n , but upon in c r e a s e d thermolysis times (88 h r s ) , 82_ was converted to a mixture of f i v e products i n the r a t i o of 1.1 : 1.0 : 3.3 : 1.6 : 1.2. The f i r s t of these i s d i e s t e r 82. The remaining products were not i d e n t i f i e d . D) CYCL0N0NA-2,6-DIENONE 99 Synthesis of 9,9-Dibromobicyclo[6.1.0]non-4-ene (123). Dry t-BuOH (1 1.) was poured i n t o a flame 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 mechanical 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. Potassium metal (50 g, 1.28 mole) was added w i t h s t i r r i n g to the t-BuOH. R e f l u x i n g proved necessary to completely react l a s t t r a c e s of potassium. The c l e a r pale y e l l o w s o l u t i o n was then d i s t i l l e d to remove the t-BuOH at a pot temperature of 90°C. When the potassium t-butoxide came out of s o l u t i o n , 200 mis of pentane were added and then removed by d i s t i l l a t i o n . T h i s was repeated s i x times. Heating 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 in pentane was cooled i n a salt-ice bath. To this cooled suspension was added cyclooctadiene (107 g, 1.0 moles). Then, with s t i r r i n g , a pentane (200 ml) solution of bromoform (253 g, 1.0 mole) was added dropwise over a period of 5 hrs. The mixture was then stirred over-night at room temperature. It 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[ ' ]-decane, mp 179°-182° uncor ( l i t . mp 174°-180°). The f i l t r a t e was separated into an aqueous layer and a pentane layer. The aqueous layer was extracted once with ether (200 mis). 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 in vacuo to give 181.4 g of a clear dark orange-red li q u i d , bp 51.5°-52.5° at 0.008 mm. Tic (20% benzene-pentane) indicated the presence of only one product. Compound 123 showed the following spectral characteristics: i r (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 0, C,, and C, CH.). — — 1 O — / j D / —i. Synthesis of 2-Bromo-3-acetoxy-trans,cis-cyclonona-1,6-diene (124). An acetic acid (675 ml) of compound 123 (142 g, 0.507 mole) and AgOAc (87 g, 0.52 mole) was stirred 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 precipitated AgBr formed, and diluted with 400 ml of water and 400 ml of ether. The layers were separated and the aqueous layer was extracted with ether (2 x 400 ml). 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 solution (2 x 100 ml). The - 114 -ether was dried (MgSO^) and removed in vacuo to give 112 g of light yellow liquid. Tic (benzene) indicated that a l l the starting material (123) was gone and only the acetate (124) was present. Compound 124 was found to possess the following spectral properties: i r (neat) 5.77 (C=0) and 6.08 (HC=CBr) y ; nmr (CC±4) T 4.00 (t, 1, CH=CHBr), 4.67 (m, 2, CH=CH), 4.97 (m, 1, CHOAc), 7.97 (s, 3, 0C0CH_3), and 7.53-8.53 (m, 8, C 4, C 5, C g, and C g 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) in 700 ml of methanol was stirred at room tempera-ture under nitrogen for 6 hrs. After this period t i c (10% ether-benzene) indicated the absence of starting material and the appearance of one new product. The methanol was removed in vacuo, water added, and the mixture extracted with 200 ml of ether. The aqueous layer was neutralized 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 (MgS04). The ether was removed in vacuo to give 85 g of a wet yellow solid. This was recrystallized from ether-hexane, after treatment with Norit, to give 49.5 g of white crystals, mp 80°-83°. A second recrystallization raised the mp to 88.5°-89°. Compound 125 gave the following spectral data: i r (CHC13) 2.94 (OH) and 6.12 (C=C) u; nmr (CC14) x 4.20 (t, 1, CH=CHBr), 4.70 (m, 2, CH=CH), 6.03 (m, 1, CHOH), and 7.50-8.70 (m, 9, C,, C , C R, and C q CH„ and C„ OH). 101 Synthesis of trans,cis-Cyclonona-2,6-dienol (127). A solution of 125 (6 g, 0.0276 mole) in ether (200 ml) was added dropwise over a - 115 -period of 20 min to a stirred, refluxing solution of sodium (11.3 g, 0.492 mole) in liquid NH^ (200 ml). The mixture was stirred for an additional 40 min. 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^). The ether was removed in vacuo to give 3.181 g (85%) of a colorless liquid. Tic (20% ether-benzene) indicates that there i s only one new product present. After Kugelrohr d i s t i l l a t i o n compound 127 gave the following spectral data: i r (neat) 2.97 (OH), 6.03 (C=C) y; nmr (CC14) x 4.14-5.12 (m, 4, CH=CH), 5.80-6.18 (m, 1, CHOH), 6.76 (s, 1, C OH), and 7.56-8.84 (m, 8, C^, C 5 > C g and C g CH 2). Anal. Calcd for CgH^O: C, 78.28; H, 10.14. Found: C, 78.19; H, 10.04. - 116 -BIBLIOGRAPHY 1. P. E. Eaton and T. W. Cole, J r . , J . Amer. Chem. S o c , 86, 962 (1964). 2. J . F . Bagli and T. Bogri, Tetrahedron L e t t . , 1639 (1969). 3. N. J . Turro, "Molecular Photochemistry," W. A. Benjamin, Inc . , New York, New York 10016, 1967. 4. E . F . UlLman, Acc. Chem. Res. , 1, 353 (1968). 5. J . G. Calvert and J . N. 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