Electroorganic Reactions Mediated by Vitamin B12 Model Complexes

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Abstract

Vitamin B12-dependent enzymes, involving the cobalt species as a catalytic center, mediate various isomerization reactions accompanied by carbon-skeleton rerragements. In order to simulate the catalytic functions of vitamin B12 as excerted in the hydrophobic active sites of enzymes concerned, we have been dealing with hydrophobic vitamin B12 derivatives which have ester groups in place of the peripheral amide moieties of the naturally occurring vitamin B12. In this work, the carbon-skeleton rearrangements as mediated 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 effectively via formation of anionic intermediates. These reactions can be also applied to the ring-expansin reactins. We have carried out the electrolysis of an alkyl halide having two ester groups and one phenyl group on the β-carbon atom in the presence of a catalytic amount of the hydrophobic vitamin B12. The migration of the pheny group was observed under the conditions forming a radical intermediate. The ester-migrated product was detected under the conditions forming an anionic intermediate. This is the first successful example in selecting a migrating group by electroylsis potential. We have also prepared a strapped hydrophobic vitamin B12 in order to change the enantioselectivity. The controlled-potential electrolysis of a racemic alkyl halide having phenyl, methoxy, and carboxylic ester groups on the same carbon atom was carried out. The simple hydrophobic vitamin B12 tends to bind S-enantiomers more favorably. On the other hand, strapped hydrophobic vitamin B12 acts to bind R-enantiomers more favorably. These results suggested that the stability of alkylated complexes was dominated the enantioselectivity of reduction products.

Original languageEnglish
Pages (from-to)63-71
Number of pages9
JournalYuki Gosei Kagaku Kyokaishi/Journal of Synthetic Organic Chemistry
Volume54
Issue number10
Publication statusPublished - Dec 1 1996

All Science Journal Classification (ASJC) codes

  • Organic Chemistry

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