Photochemical electron-transfer reactions of 1,1-diarylethylenes

Abstract

The dimerizations, nucleophilic additions, and oxygenation reactions of 1,1-diarylethylene (1), induced by photoexcited cyanoanthracenes, have been investigated. 1,1-Diphenylethylene (1a) yields 2 + 2 and 2 + 4 cyclodimers and one dehydrodimer, whereas 1,1-dianisylethylene (1b) gives two dehydrodimers, and 1,1-bis(4-(dimethylamino)phenyl)ethylene (1c) forms no dimers. Formation of the dehydrodimers is accompanied by reduction of the cyanoanthracene sensitizer. For the dimerization of 1b, the quantum yields and product ratios can be altered by the addition of quinones. The hydroquinone then replaces the reduced sensitizer. The reaction constant for nucleophilic addition of methanol to 1a/sup .+/ is 1.6 x 10/sup 9/ M/sup -1/s/sup -1/; for addition to 1b/sup .+/ it is approx.10/sup 7/ M/sup -1/s/sup -1/. Methanol does not add efficiently to 1c/sup .+ / . Photooxygenation of the diarylethylene yields mainly the corresponding 3,3,6,6-tetraaryl-1,2-dioxane in a chain process. In the presence of methanol and oxygen, 1a yields mainly 1-hydroperoxy-2-methyoxy-1,1-diphenylethane.