1987 Fiscal Year Final Research Report Summary
Catalytic Asymmetric syntheses Using Vitamin B_<12> as a Chiral Catalyst
| Project/Area Number |
61470092
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
Synthetic chemistry
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| Research Institution | Technological University of Nagaoka |
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Principal Investigator |
OGOSHI Hisanobu Professor of Technological University of Nagaoka, 工学部, 教授 (90026188)
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| Co-Investigator(Kenkyū-buntansha) |
SUZUKU Akihiro Assistant Professor of Nagaoka Technical College, 工業化学科, 助手 (60179190)
TOI Hiroo Assustant Professor of Technological University of Nagaoka, 工学部, 助手 (90126475)
AOYAMA Yasuhiro Associate Professor of Technological University of Nagaoka, 工学部, 助教授 (00038093)
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| Project Period (FY) |
1986 – 1987
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| Keywords | VITAMIN B_<12> / MICHAEL ADDITION / CYCLOPROPANES / ASYMMETRIC REDUCTION / 有機金属化合物 |
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| Research Abstract |
Vitamin B_<12> reacts with cyclopropanes having electron-withdrawing substituents such as acetyl, methoxycarbonyl, and cyano groups to give 3-substituted propyl-cobalt complexes. The alkylation with prochiral 1-acetyl-1-aklylcyclopropanes results in an asymmetric induction (ee 24-33%) at carbon 3 in the resulting alkyl ligands. Examination of the ^1H NMR spectra of the alkylation products indicates that (1) two prochiral methyl groups in 3,3-diacetylpropyl- and 3,3-bis(methoxycarbonyl)propyl-cobalt complexes are rendered diastereotopic by the presence of the chiral B_<12> and are observed to be spectroscopically nonequivalent and (2) enantiomeric methyl groups in 3-acetyl-3-alkylpropyl- and 3-acetyl- 3-(methoxycarbonyl)propyl-cobalt complexes having an asymmetric center at carbon 3 are also rendered diastereotopic and spectroscopically distinguishable in a similar manner.
The Co-C derivatives thus obtained undergo photochemical homolysis to give Co(II) and alkyl radicals which abstract a hyrogen atom from isopropanol. Thus, B_<12> catalyzes the ring-cleavage reduction of cyclopropanes in 15% aq. NH_4 Cl-isopropanol (1:1) containg Zn dust under photochemical conditions. When 1-phenyl-1-methoxycarbonylcyclopropane is used as substrate substantial asymmetric reduction is observed. In the presence of Michael olefins (methyl acrylate, methacrylate, or crotonate), B_<12> also catalyzes the Michael addition of cyclopropane-derived C-3 unit. The mechanism involves (1) photochemical homolysis of a Co-C derivative to give Co(II) and an alkyl radical, (2) homolytic Michael addition of the radical to a Michael acceptor, (3) hydrogen abstraction of the resulting ardical from isopropanol, (4) Zn reduction of Co(II) to Co(I), and (5) reaction of Co(I) with the cyclopropane to regenerate Co-C derivative.
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