PHOTOCHEMISTRY OF CONJUGATED POLYACETYLENES - [2-PHENYL-1,3,5-HEXATRIYNES WITH SOME OLEFINS(2] PHOTOCYCLOADDITION OF 1)

Irradiation of 1-phenyl-1,3,5-hexatriynes with various olefins in meth ylene chloride yields [2+2] type 1:1 photoadducts. The photoreaction p roceeds through a triplet excited state and shows site selectivity and regioselectivity. Olefins with electron-withdrawing substituents, suc h as dimethyl fumarate, fumaronitrile, acrylonitrile, methyl acrylate, and styrene, are more reactive than electron-rich olefins, suggesting that the triplet excited states of 1-phenyl-1,3,5-hexatriynes have a nucleophilic radical character.