The asymmetric Michael process involving chiral imines: structure of (±)-p-nitrobenzyl 2-(2,2-dimethyl-1-phenylpropylamino)-1-cyclopentene-1-carboxylate

Abstract

The enantioselective synthesis of quatemary carbon centres through Michael-type alkylation of chiral imines proceeds with high enantiomeric excess with 1-phenylethylamine as auxiliary, while 2,2-dimethyl-1-phenylpropylamine was found to be completely inactive. The crystal structure of a non-reactive be based on the latter auxiliary reveals a conformation identical with that of the reactive and highly selective 1-phenylethylamine. The phenyl ring is almost perpendicular to the enamino ester plane (torsion angle C-N-C-Ph 71.8 o ). The enamino ester group is planar and is stabilized by a hydrogen bond between the imine group and the carbonyl group of the ester