Two Methods for Catalytic Generation of Reactive Enolates Promoted by a Chiral Poly Gd Complex: Application to Catalytic Enantioselective Protonation Reactions
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- 作者：Masataka Morita ; Ludovic Drouin ; Rie Motoki ; Yasuaki Kimura ; Ikuo Fujimori ; Motomu Kanai* ; Masakatsu Shibasaki*
- 刊名：Journal of the American Chemical Society
- 出版年：2009
- 出版时间：March 25, 2009
- 年：2009
- 卷：131
- 期：11
- 页码：3858-3859
- 全文大小：123K
- 年卷期：v.131,no.11(March 25, 2009)
- ISSN：1520-5126
文摘
A chiral polynuclear Gd complex derived from Gd(OiPr)3 and FujiCAPO (2 or 3) catalytically generated Gd enolates through two distinct methods; transmetalation from enol silyl ethers and conjugate addition of cyanide to α,β-unsaturated N-acyl pyrroles. These chiral enolates can be enantioselectively protonated by a proton in an asymmetric environment in the polynuclear catalyst. Thus, catalytic enantioselective protonation of enol silyl ethers was promoted by the Gd catalyst (5−10 mol %) in the presence of a stoichiometric amount of 2,6-dimethylphenol. Kinetic studies and dependencies of the enantioselectivity on the silyl group structure and the proton source suggest that the reaction proceeds through a Gd enolate generated through transmetalation. Moreover, the same Gd complex (5−10 mol %) promoted conjugate addition of a cyanide−enantioselective protonation sequential reaction from α,β-unsaturated N-acyl pyrroles. Because Gd isocyanide was determined to be the active nucleophile in the conjugate addition catalyzed by the Gd complex, enantioselective protonation likely proceeded through a Gd enolate in this case as well. The products are versatile dual functional chiral building blocks for organic synthesis.