Under nitrogen protection, 1-(tert-butoxycarbonyl)-2-pyrrolidinone (2.3 g, 12.4 mmol) was dissolved in tetrahydrofuran (100 mL) and cooled to -78°C. Bis(trimethylmethylsilyl)lithium amide (1.0 M solution of THF, 16.1 mL, 16.14 mmol) was added slowly and dropwise, keeping the temperature at -78 °C. The reaction mixture was stirred at -78 °C for 30 min. Subsequently, methyl chloroformate (1.72 mL, 22.22 mmol) was added dropwise and stirring was continued at -78 °C for 1 hour. Upon completion of the reaction, the reaction was quenched with saturated ammonium chloride solution (40 mL) and extracted with ethyl acetate (100 mL x 3). The organic phases were combined, washed with brine (100 mL x 2), dried over anhydrous sodium sulfate, filtered and concentrated. The residue was purified by fast column chromatography (eluent: 0-30% petroleum ether solution of ethyl acetate) to afford methyl 1-Boc-2-oxopyrrolidine-3-carboxylate (1.9 g, 63% yield).1H NMR (400 MHz, CDCl3) δ 3.89-3.78 (m, 1H), 3.74 (s, 3H), 3.72-3.69 (m, 1H), 3.56-3.69 (m, 1H). 1H), 3.56-3.53 (m, 1H), 2.41-2.37 (m, 1H), 2.26-2.21 (m, 1H), 1.53 (s, 9H).
