Development, Mechanism, and Scope of the Palladium-Catalyzed Enantioselective Allene Diboration

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• 作者：Heather E. Burks ; Shubin Liu ; James P. Morken
• 刊名：Journal of the American Chemical Society
• 出版年：2007
• 出版时间：July 18, 2007
• 年：2007
• 卷：129
• 期：28
• 页码：8766 - 8773
• 全文大小：208K
• 年卷期：v.129,no.28(July 18, 2007)
• ISSN：1520-5126

文摘

In the presence of a chiral phosphoramidite ligand, the palladium-catalyzed diboration of allenescan be executed with high enantioselectivity. This reaction provides high levels of selectivity with a rangeof aromatic and aliphatic allene substrates. Isotopic-labeling experiments, stereodifferentiating reactions,kinetic analysis, and computational experiments suggest that the catalytic cycle proceeds by a mechanisminvolving rate-determining oxidative addition of the diboron to Pd followed by transfer of both boron groupsto the unsaturated substrate. This transfer reaction most likely occurs by coordination and insertion of themore accessible terminal alkene of the allene substrate, by a mechanism that directly provides the ³-allyl complex in a stereospecific, concerted fashion.