Step ii: Synthesis of tert-butyl 2,4-dioxopiperidine-1-carboxylate
To a 250 mL round-bottomed flask was added 3-((tert-butoxycarbonyl)amino)propanoic acid (4 g, 0.0211 mol), Meldrum acid (3.66 g, 0.0253 mol), 4-dimethylaminopyridine (3.92 g, 0.0316 mol) and anhydrous dichloromethane (100 mL). After the reaction mixture was cooled to 0 °C, EDCI-HCl (6.01 g, 0.0316 mol) was added to the same flask. The reaction mixture was stirred at room temperature for 12 hours. After completion of the reaction, the reaction mixture was diluted with dichloromethane and washed with 5% aqueous potassium bisulfate. The organic layer was separated, washed with saturated brine and dried over anhydrous sodium sulfate. The solvent was removed by concentration under reduced pressure to give the crude product. The crude product was dissolved in ethyl acetate (100 mL) and refluxed for 4 hours. The volatiles were evaporated under reduced pressure to give tert-butyl 2,4-dioxopiperidine-1-carboxylate (3.2 g, 71% yield).
1H NMR (300 MHz, CDCl3): δ 4.12 (t, 2H), 3.51 (s, 2H), 2.64 (t, 2H), 1.55 (s, 9H).
LCMS: 211.9 (M-H)+.
