A. Esteves, D. M. Goken, L. Klein
Nov 1, 2005
Citations
0
Influential Citations
21
Citations
Journal
European Journal of Organic Chemistry
Abstract
Reductive intramolecular cyclization of ethyl 2-bromo-3-(3′,4′-methylenedioxyphenyl)-3-(propargyloxy)propanoate(1) and ethyl 3-allyloxy-2-bromo-3-(3′,4′-dimethoxyphenyl)propanoate (2) promoted by (1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane)nickel(I), [Ni(tmc)]+, electrogenerated at glassy-carbon cathodes in dimethylformamide containing tetraalkylammonium salts, has been investigated. Cyclic voltammograms for reduction of [Ni(tmc)]2+ in the presence of 1 and 2 reveal that [Ni(tmc)]+ catalytically reduces these two compounds at potentials significantly more positive than those required for direct reduction of the bromo esters. During controlled-potential electrolyses of solutions of [Ni(tmc)]2+ in the presence of 1 and 2, catalytic reduction of each substrate proceeds by one-electron cleavage of the carbon–bromine bond to form a radical intermediate that undergoes cyclization to afford, respectively, ethyl 2-(3′,4′-methylenedioxyphenyl)-4-methylenetetrahydrofuran-3-carboxylate (3) and ethyl 2-(3′,4′-dimethoxyphenyl)-4-methyltetrahydrofuran-3-carboxylate (6). A mechanistic Scheme is proposed to account for the formation of each major product. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)