A dichloromethane (50 mL) solution of di-tert-butyl dicarbonate (10.30 g, 47.2 mmol) was slowly added dropwise to a dichloromethane (50 mL) solution of crude ethyl 3-pyrrolidinecarboxylate (7.12 g) at 0 °C for a controlled time of 10 min or more. The reaction mixture was gradually warmed up to room temperature over 18 h. The mixture was washed with water and saturated saline, dried over anhydrous sodium sulfate, and concentrated under reduced pressure to afford ethyl N-Boc-3-pyrrolidinecarboxylate (10.4 g, 100% yield), which could be used for the subsequent reaction without further purification.1H NMR (CDCl3) δ: 4.14 (q, 2H), 3.27-3.69 (m , 4H), 3.02 (m, 1H), 2.07-2.16 (m, 2H), 1.46 (s, 9H), 1.27 (t, 3H).
