Hydrophobic vitamin B₁₂. X.^F steric effect in electrochemical carbon-skeleton rearrangement catalyzed by hydrophobic vitamin B₁₂in nonaqueous media

A steric effect in the carbon-skeleton rearrangement catalyzed by heptamethyl cobyrinate perchlorate, [Cob(II)7C₁ester]ClO₄, was investigated under electrochemical conditions. The controlled-potential electrolyses of alkyl halides having two carboxylic ester groups of different bulkiness on the same carbon atom, such as 2, 2-bis(ethoxycarbonyl)-l-bromopropane, I-bromo-2-tert-butoxycarbonyl-2-ethoxycarbonylpropane l-bromo-2-cyclohexyloxycarbonyl-2-ethoxycarbonylpropane, and l-bromo-2-ethoxy-carbonyl-2-phenoxycarbonylpropane, were carried out in N, N-dimethylformamide, as catalyzed by [Cob(II)7C₁ester]ClO4 to give the corresponding ester-migrated products in the dark at — 1.5 V vs SCE in the presence of acetic acid and at —2.0 V vs SCE without acetic acid. As regards a correlation between bulkiness of an ester group and a migration aptitude, a smaller ester group tends to migrate to the adjacent carbon atom more readily than a larger one. The origin of such a steric effect is discussed with attention to the rate-determining step.