STEREOSELECTIVE RING-OPENING OF CHIRAL OXAZOLIDINES BY REFORMATSKY REAGENTS - AN ENANTIOSELECTIVE ENTRY TO BETA-AMINO ESTERS

Chiral oxazolidines obtained by condensation of aldehydes with (-).(R)- or (+).(S)-N-benzylphenylglycinol react with the Reformatsky reagent derived from ethyl bromoacetate, in mild reaction conditions (Et2O or CH2Cl2, O-degrees-C, 15-60 min), leading to ethyl beta-amino carboxylates in moderate to good diastereomeric excess (60-92%). These ring opening products are transformed into primary beta-aminoesters, in one step, by debenzylation with H-2/Pd on carbon without loss of their stereochemical integrity. In this way, ethyl beta-amino carboxylates can be obtained in both enantiomeric forms, with chemical yields ranging 55-76% and moderate to good e.e. (60-92%).