Cu(I)-Catalyzed Asymmetric Michael Addition of Grignard Reagents to α,β-Unsaturated Esters

Abstract

In this article, an extension to the Cu(I)-catalyzed asymmetric Michael addition of various Grignard reagents to α , β-unsaturated ­esters is presented. CuI along with the chiral Tol-BINAP ligand is used as catalyst system in this reaction. A major advantage to previously described methods is the unproblematic addition of bulky alkyl and homoallylic Grignard reagents which still gives high enantioselectivities and good to excellent yields. The authors also report that the absolute stereochemistry of the products resulting from the asymmetric Michael addition can be reversed with equally good enantioselectivities by using either the enantiomer of the chiral ligand or by using the geometrical isomer of the respective unsaturated ester.