Reductive intramolecular cyclization of D-glucose-based unsaturated substrates by indirect electrochemical approach in “Green” media

摘要

Radical cyclisation continues to be a central methodology for the preparation of natural products containing heterocyclic rings.Hence, some electrochemical results obtained by cyclic voltammetry and controlled-potential electrolysis in the study of electroreductive intramolecular cyclisation of ethyl (2S, 3R)-2-bromo-3-propargyloxy-3-(2’,3’,4’,6’-tetra-O-acetyl-β-D-glucopyranosiloxy) propanoate (1) promoted by (1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetra-decane)nickel(I), [Ni(tmc)]+,electrogenerated at glassy carbon cathodes in ethanol and ethanol/water mixtures containing tetraalkylammonium salts, arepresented.During controlled-potential electrolyses of solutions containing [Ni(tmc)]2+ and acetylated D-glucose-based bromo propargyl ester (1) catalytic reduction of the latter proceeds via one-electron cleavage of the carbon–bromine bond to form a radicalintermediate that undergoes cyclization to afford the substituted tetrahydrofurans.