Recyclable chiral Cu(II) macrocyclic salen complex catalyzed enantioselective aza-Henry reaction of isatin derived N-Boc ketimines and its application for the synthesis of β-diamine

Abstract

Recyclable chiral Cu(II) macrocyclic salen complex Cu(II)-7 generated in situ efficiently catalyzed asymmetric aza-Henry reaction of various isatin derived N-Boc ketimines with nitromethane as nucleophile at RT to give a high yield (88%) of β-nitro amines with excellent chiral induction (ee, up to 99%) with the added advantage of six times catalyst recyclability. This catalytic system also worked well with nitroethane and nitropentane to furnish the corresponding products in moderate yields with high enantioselectivities for major diastereomers. This protocol is also used for the synthesis of enantiomerically pure (S)-β-diamines via asymmetric aza-Henry reaction of N-Boc ketimine (1b) in two steps in good yield with high enantioselectivity.