Asymmetric synthesis of amines using a chiral, non-racemic, benzylidene sulfinamide derived from a recoverable precursor

Abstract

The homochiral cyclic sulfinamide S_(s)R-(+)-1 has been employed for the asymmetric synthesis of α-substituted benzylamines via the benzylidene sulfinamides R_(s)R-(–)-4. Following diastereoselective reduction and hydrolysis S_(s)R-(+)-1 can be recycled in one step from the sulfinic acid 11. The addition of zinc(II) bromide reverses the diastereoselectivity of the diisobutylaluminium hydride (DIBAL) reduction of the substrates 4. The same reversal is not observed in the reactions of analogues lacking an amide side chain. In one case the required benzylidene sulfinamide exists in the form of an enamine 15, the X-ray crystallographic structure of which is also featured. A second approach to chiral amines, via the addition of Grignard reagents to sulfinylamines derived from S_(s)R-(+)-1, is also described.