To a round-bottomed flask containing methyl azetidine-3-carboxylate hydrochloride (3 g, 20 mmol), THF (30 mL), and H2O (30 mL) was slowly added aqueous NaOH solution (4 M, 5 mL, 20 mmol) at 0 °C. Subsequently, benzyl chloroformate (2.84 mL, 20 mmol) was added dropwise at the same temperature. The reaction mixture was stirred vigorously at room temperature for 18 hours. Upon completion of the reaction, the mixture was concentrated in vacuum to remove the solvent. The residue was partitioned between Et2O (100 mL) and H2O (30 mL). The aqueous phase was back-extracted with Et2O (3 x 50 mL) and all organic phases were combined and dried with anhydrous Na2SO4. The dried organic phase was concentrated in vacuum to afford methyl 1-Cbz-azetidine-3-carboxylate (5 g, 99% yield) as a colorless oil, which was directly used in the subsequent reaction without further purification.1H NMR (400 MHz, CDCl3): δ 7.43-7.25 (m, 5H), 5.10 (s, 2H), 4.23-4.13 (m, 4H) , 3.74 (s, 3H), 3.38 (q, J=7.2Hz, 1H).
