Asymmetric synthesis of chiral amines via nucleophilic addition to ferrocenylalkyl substituted imines

Abstract

The isomerically pure imine ( Ia) formed from 1-ferrocenylethyl amine and benzaldehyde undergoes diastereoselective nucleophilic attack (Me −, D −) on the NC double bond to give ca. 67 33 mixtures of diastereomeric amines. The stereochemical outcome can be rationalised in terms of nucleophilic attack on the conformation of Ia in which allylic 1,3-strain is minimised. The opposite stereochemistry is favoured in the reduction by hydride of the related imine ( Ib) formed from 1-ferrocenylethyl amine and methylphenyl ketone. These processes provide a useful new method for the asymmetric synthesis of amines from which the chiral ferrocenyl auxiliary may be readily regenerated.