Asymmetric catalysis with self‐organized chiral lanthanum complexes: Practical and highly enantioselective epoxidation of α,β‐unsaturated ketones

Abstract

Abstract A highly efficient and practical method for obtaining α,β‐epoxy ketones with high optical purities was developed. The chiral lanthanum complex self‐organized in situ from lanthanum triisopropoxide, ( R )‐BINOL, triarylphosphine oxide, and alkyl hydroperoxide (1:1:1:1) was found to catalyze the epoxidation of α,β‐unsaturated ketones with tert ‐butyl hydroperoxide or cumene hydroperoxide at room temperature to give the corresponding epoxy ketones in high enantioselectivities (up to >99% enantiomeric excess (ee)). A remarkably high asymmetric amplification, a positive nonlinear effect, was observed in the epoxidation of chalcone, which strongly suggests the formation of a dinuclear peroxide‐involved μ‐complex as the active catalyst. Chirality 15:83–88, 2003. © 2002 Wiley‐Liss, Inc.