The Significance of Degenerate Processes to Enantioselective Olefin Metathesis Reactions Promoted by Stereogenic-at-Mo Complexes

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• 作者：Simon J. Meek ; Steven J. Malcolmson ; Bo Li ; Richard R. Schrock ; Amir H. Hoveyda
• 刊名：Journal of the American Chemical Society
• 出版年：2009
• 出版时间：November 18, 2009
• 年：2009
• 卷：131
• 期：45
• 页码：16407-16409
• 全文大小：270K
• 年卷期：v.131,no.45(November 18, 2009)
• ISSN：1520-5126

文摘

The present study provides spectroscopic and experimental evidence demonstrating that degenerate metathesis is critical to the effectiveness of this emerging class of chiral catalysts. Isolation and X-ray characterization of both diastereomeric complexes, as well as an examination of the reactivity and enantioselectivity patterns exhibited by such initiating neophylidenes in promoting ring-closing metathesis processes, are disclosed. Only when sufficient amounts of ethylene are generated and inversion at Mo through degenerate processes occurs at a sufficiently rapid rate is high enantioselectivity achieved, irrespective of the stereochemical identity of the initiating alkylidene (Curtin−Hammett kinetics). With diastereomeric metal complexes that undergo rapid interconversion, stereomutation at the metal center becomes inconsequential, and stereoselective synthesis of a chiral catalyst is not required.