Direct electrochemical reduction of a bromo-propargyloxy ester at vitreous carbon cathodes in dimethylformamide

Cyclic voltammograms for the reduction of ethyl 2-bromo-3-(3', 4'-dimethoxyphenyl)-3-(propargyloxy)propanoate (1) at glassy carbon electrodes in dimethylformamide containing tetraalkylammoniurn salts exhibit three prominent waves corresponding to cleavage of the carbon-bromine bond and to subsequent reduction of ethyl trans-3-(3', 4'-dimethoxyphenyl)-prop-2-enoate (4). Controlled-potential electrolyses of 1 at potentials corresponding to reduction of the carbon-bromine bond afford 4 as the major product with an average yield of 56%. In the presence of a proton donor (1,1,1,3,3,3-hexafluoro-2-propanol), the quantity of 4 decreases slightly, and 2-(3',4'-dimethoxyphenyl)-3-(ethoxycarbonyl)-4-methyl-2,5-dihydrofuran (3) is obtained in moderate amount (similar to26%). We propose a mechanistic scheme whereby the major products are formed via a combination of one- and two-electron processes. (C) 2003 Elsevier B.V. All rights reserved.