The Significance of Degenerate Processes to Enantioselective Olefin Metathesis Reactions Promoted by Stereogenic-at-Mo Complexes
- 20 October 2009
- journal article
- research article
- Published by American Chemical Society (ACS) in Journal of the American Chemical Society
- Vol. 131 (45) , 16407-16409
- https://doi.org/10.1021/ja907805f
Abstract
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.Keywords
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