Step 1: Synthesis of tert-butyl 3-((dimethylamino)methylene)-4-oxopyrrolidine-1-carboxylate. 1-tert-butoxycarbonyl-3-pyrrolidinone (10 g, 54.05 mmol) was suspended in N,N-dimethylformamide dimethyl acetal (120 mL) and the reaction was stirred at 105 °C for 1 hour. Upon completion of the reaction, the reaction mixture was cooled to 0 °C. Subsequently, the solvent was removed by distillation under reduced pressure at room temperature. The residue was purified by silica gel column chromatography (eluent: dichloromethane/methanol = 60/1 to 20/1) to afford the target product tert-butyl 3-((dimethylamino)methylene)-4-oxopyrrolidine-1-carboxylate (10.78 g, 83% yield). The product was analyzed by ESI-LCMS showing m/z: 241.2 [M+1]+; 1H NMR (400 MHz, CDCl3) δppm: 7.26 (s, 1H), 4.57 (s, 2H), 3.86 (s, 2H), 3.09 (s, 6H), 1.48 (s, 9H).
