A toluene solution of ethyl 3-(tert-butoxycarbonyl-ethoxycarbonylmethyl-amino)-propionate (1.43 g, 4.7 mmol) was added slowly and dropwise to an anhydrous toluene (19 mL) suspension of potassium tert-butoxide (791 mg, 7.05 mmol) at 10 °C. The reaction mixture was stirred at 0 °C for 90 min, followed by quenching the reaction with acetic acid (500 mL). Next, pre-cooled aqueous solution of NaH2PO4-H2O (2.5 g) (25 mL) was added. The organic and aqueous layers were separated and the aqueous phase was extracted with chloroform (CHCl3). All organic layers were combined, dried with anhydrous Na2SO4 and concentrated under reduced pressure. The crude product was purified by fast column chromatography (silica gel, petroleum ether/ethyl acetate 5:1, Rf 0.44) to afford ethyl N-Boc-3-oxopyrrolidine-2-carboxylate as a yellow oil (497 mg, 41% yield). The product was confirmed by 1H NMR (CDCl3, 200 MHz) with the following main rotary isomer signals: δ 4.55 and 4.47 (s, 1H), 4.27-4.22 (m, 2H), 3.91-3.84 (m) and 3.82 (t, J = 8.2 Hz, 2H), 2.69 (t, J = 8.0 Hz, 2H), 1.49 and 1.43 ( s, 9H), and 1.30 (t, J = 7.1 Hz, 3H). The results of elemental analysis are consistent with the calculated values (C, H, N) for C12H19NO5.
