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TitleElectroreductive intramolecular cyclization of a bromo propargyloxy ester catalyzed by nickel(I) tetramethylcyclam electrogenerated at carbon cathodes in dimethylformamide
Author(s)Esteves, Ana Paula
Goken, Danielle M.
Klein, Lee J.
Lemos, Maria A.
Medeiros, Maria José
Peters, Dennis G.
Issue date2003
PublisherAmerican Chemical Society
JournalThe Journal of Organic Chemistry
Citation"The Journal of Organic Chemistry". ISSN 0022-3263. 68 (2003) 1024-1029.
Abstract(s)Cyclic voltammetry and controlled-potential electrolysis have been employed to investigate and characterize the reductive intramolecular cyclization of ethyl 2-bromo-3-(3′,4′-dimethoxyphenyl)-3-propargyloxy-propanoate (1) 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. Cyclic voltammograms for reduction of [Ni(tmc)]2+ in the presence of 1 reveal that [Ni(tmc)]+ catalytically reduces 1 at potentials more positive than those required for direct reduction of 1. During controlled-potential electrolyses of solutions containing [Ni(tmc)]2+ and 1, catalytic reduction of the latter proceeds via one-electron cleavage of the carbon–bromine bond to form a radical intermediate that undergoes cyclization to afford 2-(3′,4′-dimethoxyphenyl-3-ethoxycarbonyl-4-methylene-tetrahydrofuran (2). In the presence of a base (either electrogenerated or deliberately added as potassium tert-butoxide), 2 rearranges to give 2-(3′,4′-dimethoxyphenyl-3-ethoxycarbonyl-4-methyl-2,5-dihydrofuran (3). A mechanistic scheme is proposed to explain the results obtained by means of cyclic voltammetry and controlled-potential electrolysis.
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