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The significance of degenerate processes to enantioselective olefin metathesis reactions promoted by stereogenic-at-Mo complexes.

Authors
Type
Published Article
Journal
Journal of the American Chemical Society
1520-5126
Publisher
American Chemical Society
Publication Date
Volume
131
Issue
45
Pages
16407–16409
Identifiers
DOI: 10.1021/ja907805f
PMID: 19842640
Source
Medline
License
Unknown

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.

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