Optically pure 2,3-cis-disubstituted piperidines 7a and 7b have been prepared from chiral lactams 2. The first step involves C-2 functionalization with Grigard reagent, then a diastereoselective reduction of resulting oxazolidines 5 furishes the desired piperidines 7.
A series of 3-substituted piperidines in enantiomerically pure form has been synthetized from lactam 3 by a stereospecific route involving a postulated rigid amide enolate. This strategy has been applied to the synthesis of (+)-stenusine 10.