(S)-2-(Aminomethyl) butanedioic acid (6) can been synthesised by stereoselective alkylation of the Na enolates of acyloxazolidinones 1a and 1b with methyl bromoacetate, then oxidation of the vinyl or dimethoxyphenyl substituent to a carboxyl group, followed by Curtius rearrangement and deprotection. The absolute configuration of 6 has been correlated with that of (S)-1-phenylethylamine by a combination of crystallographic and chemical means.