Ethyl 3-[N-benzyloxycarbonyl-N-(ethoxycarbonylmethyl)amino]propanoate (26.8 g, 79.5 mmol) was used as a raw material and dissolved in ethanol (200 mL). To this solution was added an ethanolic solution of 20% sodium ethanolate (40.6 mL, 119.3 mmol), followed by heating and refluxing the reaction mixture for 2 hours. Upon completion of the reaction, the solvent was removed by concentration under reduced pressure and the residue was dissolved in water (100 mL). The aqueous solution was acidified by slowly adding concentrated hydrochloric acid to the aqueous solution under cooling in an ice bath and extracted with chloroform (100 mL x 3) after acidification. The chloroform extracts were combined, washed with saturated aqueous sodium chloride solution (100 mL) and then dried with anhydrous sodium sulfate. After drying, the filtrate was filtered and the filtrate was concentrated under reduced pressure to obtain the crude product. The crude product was purified by silica gel column chromatography (eluent: hexane/ethyl acetate, 2:1) to give 16.7 g of ethyl N-Cbz-4-oxo-3-pyrrolidinecarboxylate in 72% yield as a light brown oil. The product was characterized by 1H-NMR (400 MHz, CDCl3) and MS (ESI): 1H-NMR δppm: 1.25-1.33 (3H, m), 3.87-4.37 (7H, m), 5.16-5.22 (2H, m), 7.23-7.41 (5H, m); MS (ESI) m/z: 314 (M + Na) + . .
