32315-10-9

2177-63-1

13590-42-6

Under argon protection, 4.5 g of L-aspartic acid-4-benzyl ester was added to a 500 mL three-necked flask with 300 mL of freshly distilled anhydrous ethyl acetate, heated to 90 °C and refluxed for 30 min. Subsequently, 2.7 g of triphosgene was dissolved in 60 mL of freshly distilled ethyl acetate and slowly added dropwise to the reaction system through a constant pressure dropping funnel. Refluxing was maintained at 90 °C until the reaction solution became clear and transparent. Upon completion of the reaction, the reaction solution was rapidly cooled in an ice-salt bath for 30 min. The cooled reaction solution was washed sequentially with cold saturated sodium bicarbonate solution three times and cold saturated sodium chloride solution twice. The organic phase was separated and dried with anhydrous sodium sulfate for 30 minutes. The desiccant was removed by filtration and the filtrate was concentrated under reduced pressure and precipitated by the addition of freshly distilled anhydrous petroleum ether. The white solid product was collected by filtration and purified by recrystallization from ethyl acetate. White needle-like crystals were finally obtained in 83% yield.