Highly efficient enantioselective epoxidation of α,β-enones catalyzed by cheap chiral lanthanum and gadolinium alkoxides

Abstract

( S)-6,6′-Dibromo-BINOL and ( S)-6,6′-diphenyl-BINOL have been developed as efficient chiral ligands applicable to lanthanoid catalyzed asymmetric epoxidation of α,β-unsaturated ketones in the presence of cumene hydroperoxide. Excellent chemical yield and enantioselectivity have been achieved for several epoxides at room temperature by using 5 mol% of La( O- i-Pr) 3-( S)-6,6′-dibromo-BINOL and Gd( O- i-Pr) 3-( S)-6,6′-diphenyl-BINOL, respectively. Up to 95% ee was obtained for epoxychalcone with Gd( O- i-Pr) 3-( S)-6,6-diphenyl-BINOL catalyst at room temperature. A plausible catalyst structure as well as the catalytic cycle has also been suggested.