Enantioselective synthesis of α-hydroxy-β-amino acids from α-amino acids mediated by sulfoxides

The synthesis of the optically pure (2S,3S)- and (2R,3S)-3-amino-2-hydroxybutanoic acids from commercially available (S)-alanine derivatives is reported. The key step of the synthetic sequence is the conversion of γ-amino sulfoxides into γ-amino alcohols by treatment with TFAA and sym-collidine. The efficiency of this non-oxidative Pummerer reaction (NOPR) is dependent on the stereochemistry of the starting sulfoxide.