Iron-catalyzed Michael reactions revisited: a synthetically useful process for the preparation of tri-carbonyl compounds and chiral warfarin

The LBAs (Lewis acid-assisted Bronsted acid catalysis) is proposed as possible mechanistic process in the simple FeCl3-catalyzed Michael reactions of chalcones with active methylene compounds in organic solvents. And iron salts were found to be effective promoters in the asymmetric Michael addition of 4-hydroxycoumarin to alpha,beta-unsaturated ketone, which resulted in excellent yield and high level of enantioselectivity (up to 91% ee) in the presence of low catalytic amount of iron and simple chiral primary amine. Crown Copyright (C) 2010 Published by Elsevier Ltd. All rights reserved.