To a solution of tetrahydrofuran (THF, 62 mL) of tert-butyl (S)-5-oxopyrrolidine-2-carboxylate (2.29 g, 12.4 mmol) was added sodium hydride (NaH, 60% Oil Dispersion, 546 mg, 13.6 mmol, 1.1 eq.), and stirred for 30 min at room temperature. Benzyl chloroformate (1.94 mL, 13.6 mmol, 1.1 eq.) was then added and stirring was continued for 20 hours. Upon completion of the reaction, the solvent was removed by evaporation under reduced pressure, saturated aqueous ammonium chloride (NH4Cl) (100 mL) was added and extracted with ethyl acetate (EtOAc, 2 x 100 mL). The organic phases were combined, dried with magnesium sulfate (MgSO4), filtered and concentrated under reduced pressure. Purification by silica gel (SiO2) column chromatography with the eluent of cyclohexane/ethyl acetate (3:1) afforded 1-benzyl 2-tert-butyl (S)-5-oxopyrrolidine-1,2-dicarboxylate (3.56 g, 11.1 mmol, 90% yield) as a colorless oil. Thin layer chromatography (TLC) Rf value was 0.18 (cyclohexane/ethyl acetate 3:1, potassium permanganate color development).1H-NMR (300MHz, CDCl3) δ: 1.39 (s, 9H, 3×CH3), 1.97-2.70 (m, 4H, 2×CH2), 4.54 (dd, J=9.3,2.7Hz, 1H, CH), 5.27 (dd, J=16.2,12.3Hz, 2H, CH2), 7.27-7.43 (m, 5H, Ar-H). 13C-NMR (75.5MHz, CDCl3) δ: 25.11, 27.12, 31.23, 59.60, 68.43, 82.76, 128.4, 128.6, 128.7, 135.3 , 151.1, 170.3, 173.3.
