Electrochemical reactions mediated by vitamin B12 derivatives in organic solvents

Vitamin B-12 enzymes, involving the cobalt species as a catalytic center, mediate various isomerization reactions accompanied by carbon-skeleton rearrangements. In order to simulate the catalytic functions of vitamin B-12 as exerted in the hydrophobic active sites of enzymes concerned, we have been dealing with hydrophobic Vitamin B-12 derivatives, which have ester groups in place of the peripheral amide moieties of the naturally occurring vitamin B-12. In this work, the carbon-skeleton rearrangements as mediated by hydrophobic vitamin B-12 derivatives were investigated under electrochemical conditions. The controlled-potential electrolyses of alkyl halides with various electron-withdrawing groups were carried out, and the electrochemical carbon-skeleton rearrangements proceeded effectively via formation of anionic intermediates. These reactions can also be applied to the ring-expansion reactions. We have prepared a novel vitamin B-12 derivative, [Cob(II)7Phe(OBzl)]ClO4, having phenylalanine residues on the peripheral side chains. [Cob(II)7Phe(OBzl)]ClO4 effectively catalyzed 1,2-migration of the carboxylic ester in 1-bromo-2,2-bis(ethoxycarbonyl)propane at - 1.0 V vs. SCE under irradiation conditions. A strapped hydrophobic vitamin B-12 was prepared in order to change the enantioselectivity, and the controlled-potential electrolysis of a racemic alkyl halide was carried out in the presence of vitamin B-12 derivatives. Product analyses and computational calculations suggested that the stability of alkylated complexes dominated the enantioselectivity of reduction products. (C) 2000 Elsevier Science S.A. All rights reserved.