Tert-butyl 2,4-dioxopiperidine-1-carboxylate (1 g, 4.69 mmol) was used as starting material and dissolved in anhydrous carbon tetrachloride (10 mL) with stirring. N-bromosuccinimide (0.83 g, 4.69 mmol) was added slowly at 10 °C. The reaction temperature was maintained in the range of 10-15 °C with continuous stirring for 2 hours. After completion of the reaction, the solvent was evaporated under reduced pressure. Water (10 mL) was added for dilution and the target product 3-bromo-2,4-dioxopiperidine-1-carboxylic acid tert-butyl ester was subsequently extracted with ethyl acetate (2 x 30 mL). The organic layers were combined, dried with anhydrous sodium sulfate and concentrated to obtain the crude product. Purification of the crude product by fast column chromatography resulted in the title compound in 99% yield (1.4 g, off-white solid). The structure of the product was confirmed by 1H NMR (400 MHz, DMSO-d6): δ 5.50 (s, 1H), 3.74-3.71 (m, 2H), 2.69-2.66 (m, 2H), 1.46 (s, 9H).The LCMS analysis (Method A) showed: 193.8 (M-Boc + H), retention time 2.93 min, purity 81.51% (max).
