(The) photochemistry of some polyacetylenes

Abstract

Diacetylene compound, 1,4-diphenyl-1,3-butadiyne, was photolyzed with some olefins such as 2,3-dimethyl-2-butene, methyl crotonate, dimethyl fumarate, 1,4-cyclohexadiene, and 5-fluorouracil as a model reaction of the phototoxic conjugated polyynes with DNA or RNA and obtained [2+2] photocycloadducts except for 1,4-cyclohexadiene. The reaction mixtures were irradiated with 300 nm uv light and isolated by silica gel low pressure preparative liquid chromatography or silica gel preparative thin layer chromatography. The photoreaction of 1,4-di-t-butyl-1,3-butadiyne and some olefins such as 2,3-dimethyl-2-butene and trans-1,2-dichloroethylene afforded [2+2] photoadducts. The structure of the photoadducts was determined by spectral methods and comparing uv and fluorescence spectra of the photoadducts to each other. A mechanism of the photochemical reactions of 1,4-diphenyl-1,3-butadiyne and 1,4-di-t-butyl-1,3-butadiyne with some olefins was proposed involving vinyl biradical intermediate which is the first excited singlet state of acetylene.