Chiral cyclopropenimine-catalyzed enantioselective Michael additions between benzophenone-imine of glycine esters and α,β-unsaturated pyrazolamides

Abstract

A highly enantioselective Michael addition between benzophenone-imine of glycine esters and β-substituted α,β-unsaturated pyrazolamides has been realized by using 10 mol% of a chiral cyclopropenimine (Lambert catalyst, CSB-1) as an organosuperbase catalyst under very mild conditions to afford Michael adducts in up to 95% yield and 99% ee. The pyroglutamic acid esters with two adjacent stereocenters are obtained through subsequent lactamization in quantitative yields and excellent enantioselectivities.