Stereoselective Synthesis of 4-Aminomethyl-3-hydroxyprolinols and Ring Expansion into Enantiopure Polyfunctionalized Piperidines

A stereoselective route was developed to synthesize enantiopure 3,4,5trisubstituted piperidines in few steps.The functionalities were introduced starting from (S)-pyroglutaminol as chiral material.The method is based on the 1,3dipolar cycloaddition of N-benzylnitrone to a derived bicyclic a,b-ethylenic lactam, followed by a ring enlargement of five to six membered nitrogen heterocycles through aziridinium ions.