Asymmetric Synthesis of α‑Trifluoromethylthio-β-Amino Acids under Phase Transfer Catalysis

The first asymmetric α-trifluoromethylthiolation of 2-substituted isoxazolidin-5-ones was developed using Maruoka type N-spiro ammonium catalysts under phase-transfer conditions. The resulting products, containing a trifluoromethylthiolated quaternary chiral carbon, were obtained in moderate to good yields and up to 98:2 enantiomeric ratio. Moreover, the easy N–O bond cleavage provided access to undescribed α-trifluoromethylthio-β^2,2-amino acids, with promising applications in biochemistry and medicinal chemistry.