Access to optically active 3-azido- and 3-aminopiperidine derivatives by enantioselective ring expansion of prolinols

The activation of N-alkyl prolinols by XtalFluor E allowed the formation of an aziridinium intermediate that can react with tetrabutylammonium azide (nBu(4)NN(3)) to produce 3-azidopiperidines and/or 2-(azidomethyl)pyrrolidines, in a ratio up to 100/0. These 3-azidopiperidines can be reduced to the corresponding 3-aminopiperidines.