Michael addition of N-sulfinyl metalloenamines to β-trifluoromethyl-α,β-unsaturated ester: an efficient access to chiral 4-trifluoromethyl-2-piperidones

Michael addition of N-sulfinyl metalloenamines to β-trifluoromethyl-α,β-unsaturated ester was investigated. High diastereoselectivities and excellent yields were obtained. The conversion of addition products into 4-trifluoromethyl-2-piperidones asymmetrically, which involved a DIBAL-H reduction and the following cyclization, was illustrated. The absolute configuration of Michael addition products and 4-trifluoromethyl-2-piperidones were determined by X-ray crystallographic analysis and NOESY experiment, respectively. This method affords an efficient and asymmetric approach to a variety of chiral 4-trifluoromethyl-2-piperidones.