Photochemistry of Conjugated Polyacetylenes : [2+2] Photocycloaddition of 1-Phenyl-1,3,5-hexatriynes to Some Olefins

Abstract

Irradiation of 1-phenyl-1,3,5-hexatriynes with various olefins in methylene chloride yields [2+2] type 1:1 photoadducts. The photoreaction proceeds through a triplet excited state and shows site selectivity and regioselectivity. Olefins with electron-withdrawing substituents, such 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.