Parallel solution-phase asymmetric synthesis of α-branched amines

Abstract

A general method is reported for the parallel solution-phase asymmetric synthesis of α-substituted amines based on the stereoselective addition of organomagnesium reagents to enantiomerically pure tert-butanesulfinyl imines. The sulfinyl imines are prepared in high yields by condensation of tert-butanesulfinamide with aldehydes, followed by quenching and removal of the titanium species with diatomaceous earth saturated with water. Addition of organomagnesium reagents then proceeds with high diastereoselectivities. After aqueous workup following the organometallic addition, liquid/liquid separation is readily accomplished using 1PS filter cartridges. Acidic alcoholysis of the resulting sulfinamide products, followed by acid/base extraction and isolation, affords the desired amine hydrochlorides. The effectiveness of this sequence of reaction and workup procedures was demonstrated by the parallel synthesis of 10 α-substituted amines in excellent overall yields (72-84%) and high enantiopurities (80-97% ee). Notably, all 10 amine hydrochlorides were obtained in analytically pure form without requiring chromatography or crystallization of any of the intermediates or products. Finally, reaction times can be reduced by the use of microwave irradiation in the sulfinyl imine condensation step. Sulfinyl group cleavage and concomitant resin capture using sulfonic acid resin can also be accomplished through the use of microwave irradiation.