Photochemical dimerization of methyl 2-furyl- and 2-thienylacrylate and related compounds in solution

Abstract

Irradiation of methyl 3-(2-furyl)acrylate 1 in the presence of benzophenone led to the formation of a mixture of t-3, t-4- and c-3,c-4-dimethyl 3,4-di-(2-furyl)cyclobutane-r-1, c-2-dicarboxylates 2 and 3 in 2 : 1 ratio and 90% overall yield. The reaction is an efficient synthetic method when using the corresponding acid 4, the acrylaldehyde derivative 7a and the corresponding methyl ketone 7b as well. On the other hand the presence of a methyl group on the double bond inhibited the reaction, while the presence of a methyl group on the furan ring also depressed the reactivity of the double bond, giving only a 27% yield of the corresponding dimer. Methyl 3-(2-thienyl)acrylate 13 gave a mixture of two dimers 14 and 15 in an overall yield of 25%, while methyl cinnamate showed only E-Z isomerization.