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 tetraalkylammonium 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 (26%). We propose a mechanistic scheme whereby the major products are formed via a combination of one- and two-electron processes.