Synthesis of enantiomerically pure cis-2,4-disubstituted piperidines: extension of chiral homoenolate alkylations toward the preparation of nitrogen heterocycles

Enantiomerically pure cis-2,4-disubstituted piperidines were synthesized fr om chiral thiolactam 2 in six steps via a highly diastereoselective homoeno late alkylation which set the stereochemistry at the C4 carbon. In addition , two cleavage methods were used to cleave the lactam to the desired piperi dines with a high level of diastereoselection at the newly created C2 stere ocenter. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.