Photochemistry of Cycloalkenes. 9. Photodimerization of Cyclohexene

Article abstract of DOI:10.1021/jo01310a039

The photodimerization of cyclohexene has been restudied.Either direct or triplet-sensitized irradiation produced a stereoisomeric mixture of <2 + 2> dimers 6-8, respectively, as primary products with the cis,trans isomer 7 predominating.The direct-irradiation process was complicated by the accompanying formation of the radical-derived products 3-5.Dimerization is interpreted in terms of initial light-induced cis-trans isomerization of cyclohexene, followed by a nonstereospecific ground-state<2_s + 2_a>addition of trans-cyclohexene to the cis isomer.By contrast, cycloheptene showed little tendency to undergo photodimerization; attempted p-xylene-sensitized dimerization afforded instead principally the sensitizer-olefin adducts 10 and 11.Comparison is made with the copper(I) triflate catalyzed photodimerization of cyclohexene and cycloheptene.