Novel Catalytic Functions of Hydrophobic Vitamin B₁₂ in Electrochemical Carbon-Skeleton Rearrangements

The carbon-skeleton rearrangements as catalyzed by hydrophobic vitamin B₁₂ 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 via formation of anionic intermediates. Substrates with two electron-withdrawing groups placed on the β-carbon atom with combination of one carboxylic ester and one of carboxylic ester, ace-tyl, and cyano moieties readily gave the corresponding rearrangement products which were derived from individual migration of the substituent groups. Substrates with only one of the electron-withdrawing groups, carboxylic ester, acetyl, and cyano, did not give any rearrangement product, but a substrate with one thioester group afforded the corresponding rearrangement product. The apparent migratory aptitude of electron-withdrawing groups was found to decrease in the order: COSR > COR > CO₂R > CN. A hydrophobic vitamin B₁₂ with the cyano moiety at the axial site of cobalt further enhanced the electrochemical carbon-skeleton rearrangement.