Enantioselective Epoxidation of α,β‐Enones by Electrophilic Activation with a BINOL–Zinc Catalyst

Abstract

AbstractThe combination of BINOL and a dialkylzinc reagent R2Zn affords, in situ, a catalyst for homogeneous epoxidation of (E)‐α,β‐enones to the corresponding trans‐epoxy ketones. tert‐Butyl hydroperoxide (TBHP) and cumene hydroperoxide (CMHP) are effective terminal oxidants for this process. Enantiomeric excesses of up to 96 % can be achieved conveniently at room temperature. Mechanistic investigations point towards an electrophilic activation of the substrates by the chiral BINOL–zinc catalyst and a subsequent nucleophilic attack of the oxidant. This mechanistic proposal is supported additionally by a non‐linear effect, the absolute product configuration as well as NMR studies. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)