Convenient synthesis of trans-beta-amino carboxylic esters with an azetidine skeleton via rearrangement of beta,gamma-aziridino alpha-amino esters.

A short and facile approach to biologically interesting N-protected alkyl 3-aminoazetidine-2-carboxylic esters, a new class of conformationally restricted beta-amino esters, was developed. Reduction of anti-beta,gamma-aziridino-alpha-(N-diphenylmethylidene)amino esters and subsequent regioselective intramolecular ring opening of the beta,gamma-aziridine ring via nucleophilic attack of the alpha-amino function afforded the trans-azetidines.