Butadienes 4 + 4-photocycloaddition

Many examples of photocycloaddition reactions of olefins and polyenes yielding cyclobutane derivatives have been reported. Irradiation of mixtures of butadiene and 1,1-dichloroethylene in the presence of a... 

Similar effects were observed in the photocycloaddition of isoprene and a-acetoxyacrylonitrile(55b,56) but not in the cross-addition of the acrylonitrile and cyclopentadiene.[Pg.230]

Tetramethylbenzoquinone undergoes photocycloaddition with butadiene to yield a 2 1 adduct (95)(108) ... 

Chloranil, photocycloaddition with butadiene, 474 Chlorophylls, 552 Chu, N. Y. C 439 Ciamician, G., 1, 2,459 Cinnamic acid, solid state photodimerization, 476... 

Molecular mechanics-valence bond dynamics have been used to study the model 4 + 4-photocycloadditions of butadiene with butadiene. The photoirradiation of t-butyl 9-anthroate and furan produces a mixture of 4 + 4-cycloadduct and 4 - - 4-cyclodimers. 

An interesting extension of the forementioned generalizations has recently been reported.43 When a dilute solution of 2,3-dimethyl-l,3-butadiene 11a is irradiated in the presence of a large excess of benzo-phenone, a product 16 arising from the photocycloaddition reaction is observed. This anomalous result has been explained as involving the 77,77- triplet of the diene, formed by triplet-triplet transfer from the n,n triplet of benzophenone, which then reacts with ground-state benzophenone. The critical steps are shown in structures 14-16. 

Bishop and Hamer found that acyclic a,/8-unsaturated 1,2-diketones form cyclopentanol derivatives in high yield, while / ,y-unsaturated derivatives form oxetanes by internal cycloaddition.114 Unexpectedly, the y,S-unsatu-rated derivatives also gave oxetanes after an initial migration of the double bond to the /8,y position. The formation of oxetanes such as 38 was observed in the camphorquinone sensitized dimerization of butadiene.115 Photocycloadditions of a-diketones to various olefins have been studied by several groups.116... 

With conjugated dienes, photocycloaddition of carbonyl compounds occurs at one of the double bonds to give vinyloxetanes. An interesting example is the reaction of acetone with 2-methyl-l,3-butadiene, which gave the two oxetanes (60) and (61) in a ratio of 3 1 and a total yield of about 20% (72JA8761). Other alkenes which have been used for photosynthesis of oxetanes include enol ethers, ketene acetals, enamines, allenes and diketene, with the reaction of the last compound with benzaldehyde illustrated in equation (105) (75CPB365). 

Albini et al. investigated the photocycloadditions of 1- and 2-cyanonaph-thalenes with 1,3-dienes [137]. Irradiation of 1-cyanonaphthalene in the presence of 2,3-dimethyl-l,3-butadiene in cyclohexane gave a complex mixture containing... 

Photoreactions of 9,10-dicyanophenanthrene with 1,3-butadiene gave a novel (3 + 2) photocycloadduct at the 1,10-position of the phenanthrene ring (403) to one double bond of 1,3-butadiene and a (2 + 2) cycloadducts at the 9,10-position (404,405) [366] (Scheme 108). Compound 403 was formed from the singlet excited state of 9,10-dicyanophenanthrene, and 404-405 were from triplet state of 9,10-dicyanophenanthrene. This is the first example of the (3 + 2) photocycloaddition to the phenanthrene ring. 

The utility of dioxopyrrolines in [2 + 2]-photocycloaddition reactions was comprehensively demonstrated by Sano et al. [66]. Substrate 55, for instance, underwent a clean reaction with 2-trimethylsilyloxy-butadiene to provide bicyclic HTproduct 56 as a single diastereoisomer (Scheme 6.22). Inline with previous observations [67], the vinyl group was positioned exo relative to the five-membered ring, and the silyloxy... 

Achiral butadienes 143 and 144 formed chiral mixed crystals (substitutional solid solutions) of space group P2 l lx by cooling the melts of both components or on crystallization from ethanol solution. A single large-sized mixed crystal 143144 was pulverized and irradiated resulting in [2 + 2] photocycloaddition, thereby giving the optically active heterodimers 145 as well as the achiral homodi-... 

Scheme 33 Absolute asymmetric [2 + 2] photocycloaddition in the mixed crystals of butadienes.

A theoretical study of the Diels-Alder reactions between 1,3-butadiene and, respectively, cyclopentadiene and 2H-phosphole, has revealed a remarkable similarity between the two reactions. Further studies of photocycloaddition reactions of phosphole moieties have also been reported. Transition metal complexes of phospholide anions continue to attract attention, and in particular the chemistry of phosphaferrocene systems remains a major interest . The past year has also seen significant activity in the chemistry of di- and tri-phospholes, related polyphospholide anions, and also heterodiphosphole systems. Routes have been developed to the diphosphonio-l,2-diphospholes 356,... 

Nur wenige der hier behandelten Reaktionen sind von teehnischuin Interesse - als Beispiel 3ei die Photoaddition von Chlor an Benzol genannt - einige sind jedoeh von hohem theoretischen Interesse wie etwa die Photocycloaddition von Benzol an Butadien-(], 3) zum stark gcspaimtciiBicj/c/o[4..2.2]rf [Pg.472]

The inverse electron demand Diels-Alder reaction of 1-oxa-l,3-butadiene 1 (a tautomer of triformylmethane) to dihydrofuran 2. obtained by photocycloaddition of benzaldehyde to furan, gives a mixture of two diastereomeric adducts with moderate yields and a d.r. (exolendo) 87 135. 

Photocycloadditions of 2-Trimethylsilyloxy-1,3-butadiene to 2-Cycloalkenones General Procedure46 ... 

The major effect in the photolysis of 3,4-polyisoprene is photocycloaddition of the 3,4-units analogous to that mentioned earlier for 1,2-poly butadiene [54]. 

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