54571-66-3

67-56-1

149-87-1

4931-66-2

Sulfoxide chloride (6.60 mL, 90.6 mmol) was slowly added to a solution of 5-oxopyrrolidine-2-carboxylic acid (9.00 g, 69.7 mmol) in methanol (20 mL) at 0 °C. The reaction mixture was stirred at room temperature for 16 hours. After completion of the reaction, the mixture was concentrated under vacuum. The residue was diluted with deionized water (100 mL) and extracted with ethyl acetate (100 mL). The organic phase was separated and washed sequentially with deionized water (20 mL) and saturated saline (50 mL), dried over anhydrous sodium sulfate and concentrated under vacuum to give methyl 5-oxopyrrolidine-2-carboxylate (5.60 g, 58% yield) as a colorless liquid. The product did not need further purification and could be used directly in the subsequent reaction. Mass Spectrometry (ESI) m/z [M+H]+: 144.00, retention time: 1.33 min, relative abundance: 68.6%.1H NMR (400 MHz, DMSO-d6) δ 2.04-2.18 (m, 2H), 3.56-3.62 (m, 2H), 3.70 (s, 3H), 4.16-4.22 (m, 1H). 7.97 (s, 1H).