HYDROPHOBIC VITAMIN-B-12 .14. RING-EXPANSION REACTIONS CATALYZED BY HYDROPHOBIC VITAMIN-B-12 UNDER ELECTROCHEMICAL CONDITIONS IN NONAQUEOUSMEDIUM

The electrolysis of alicyclic ketones (5, 6, 7, and 8-membered rings) with a carboxylic ester and a bromomethyl group was carried out in N,N -dimethylformamide in the presence of a catalytic amount of heptamethy l cobyrinate perchlorate under various reaction conditions. The ring-e xpansion reaction largely proceeded at -2.0 V vs sce for all the subst rates. The electrolysis plausibly proceeds as follows: the Co(II) comp lex as a catalyst is electrochemically reduced to the Co(I) species; t he corresponding alkylated complex is generated by reaction of the sup ernucleophilic Co(I) species with an alicyclic bromide; the alkylated complex is subsequently decomposed by electrolysis to afford the final products; and the cobalt complex acts as a mediator repeatedly. (C) 1 997 Elsevier Science Ltd.