Step A: Synthesis of intermediate VI
A tetrahydrofuran (THF, 500 mL) solution of benzyl 2,5-dioxopyrrolidin-1-yl carbonate (83 g, 334 mmol) was added slowly and dropwise to an aqueous (500 mL) solution of 1-aminocyclopropanecarboxylic acid (25 g, 247 mmol). A solution of sodium bicarbonate (91 g, 1088 mmol) in water (500 mL) was added dropwise to the reaction mixture under cooling in an ice bath. After the dropwise addition, the reaction system was slowly warmed to room temperature and the reaction was continued with stirring for 16 hours. Upon completion of the reaction, the solvent was removed by distillation under reduced pressure. The residue was resuspended in dichloromethane (200 mL) and extracted with water (500 mL). The aqueous phase was acidified by acetic acid and the precipitated white solid was collected by filtration to afford 1-((benzyloxy)carbonyl)amino)cyclopropanecarboxylic acid (53 g, 171 mmol, 69.2% yield). The crude product can be directly used in the next step of the reaction.LC/MS analysis result: m/z calculated value 235.1, measured value 258.0 ([M+Na]+).
