L-threo-Hydroxyaspartic acid (L-THA) is known as an L-glutamic acid mimic, so it takes role as an inhibitor of excitatory amino acid (EAA) transporters. Because L-glutamate plays an important role as a neurotransmitter in the central nervous system, the concentration of extracellular L-glutamate is strictly controlled, and L-THA can be utilized as a competitive inhibitor to control its concentration. Various synthetic methods for stereoselective synthesis of L-THA have previously been developed. In the presentation, a new stereoselective method has been developed to synthesize L-THA from the configurationally stable α-amino aldehyde, which prepared from a commercially available N-Boc-D-Ser-OH. More than 20 to 1 stereoselectivity is obtained via the stereoselective intramolecular conjugate addition of N-hydroxymethyl on α-amino aldehyde to the spontaneously formed phenylsulfonylnitroolefin by the tandem reactions between α-amino aldehyde and PhSO2CH2NO2.