To a pyridine (10 mL) solution of Boc-L-serine methyl ester (0.67 g, 3.1 mmol) cooled in an ice bath was added p-toluenesulfonyl chloride (3.0 g, 15.7 mmol). The reaction mixture was stirred in an ice bath under nitrogen protection for 8 hours. Subsequently, ether (10 mL) was added to the reaction system and the mixture was transferred to room temperature to continue stirring for 14 hours. Upon completion of the reaction, the reaction solution was washed sequentially with deionized water, 10% potassium bisulfate solution, saturated sodium bicarbonate solution and brine. The organic layer was separated, dried with anhydrous magnesium sulfate and concentrated under reduced pressure to remove the solvent. The colorless oil obtained was purified by silica gel column chromatography (eluent ratio hexane:ethyl acetate=2:1) to afford (S)-methyl 2-((tert-butoxycarbonyl)amino)-3-(p-toluyloxy)propionate (1.05 g, 91% yield) as a white solid. The spectral data of the product were in agreement with literature reports and the purity was confirmed by 1H NMR.
