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

The homochiral cyclic sulfinamide S-(S)R-(+)-1 has been employed for the asymmetric synthesis of alpha-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.