55750-48-6

541-59-3

79-22-1

55750-48-6

To a solution of ethyl acetate (120 mL) of maleimide (6.35 g, 65.4 mmol) was sequentially added N-methylmorpholine (NMM, 8.6 mL, 78.5 mmol) and methyl chloroformate (6.0 mL, 78.5 mmol) at 0 °C. The reaction mixture was stirred at 0 °C for 30 min, then brought to room temperature and continued stirring for 1 h. The reaction was completed by filtration. Upon completion of the reaction, the solid was collected by filtration and the filtrate was concentrated under reduced pressure. The concentrated residue was dissolved in dichloromethane, filtered through a silica gel column and eluted with dichloromethane to remove red impurities. The eluate was concentrated and the resulting solid was ground with a solvent mixture of ethyl acetate and petroleum ether to give a final white solid of methyl 2,5-dioxo-2,5-dihydro-1H-pyrrole-1-carboxylate (9.0 g, 88% yield).