4-Piperidones from enantiomerically pure enones. Synthesis of 6-alkylsubstituted 4-oxo-pipecolic acid derivatives

The cyclization of the enantiomerically pure alpha,beta-unsaturated ketone 1, an aliphatic aldehyde 3 and ammonia or benzylamine gives diastereoselectively cis-piperidones 4/4'. Although only modest yields were obtained, the presented cyclization has the advantage of being a single step reaction. The products 4 can serve as precursors for all-cis-4-hydroxypiperidones 5 and novel pipecolic acid derivatives 9.