541-59-3

541-41-3

55750-49-7

1) Synthesis of ethyl 2,5-dioxo-2,5-dihydro-1H-pyrrole-1-carboxylate: 9.7 g (0.1 mol) of maleimide was dissolved in a mixed solution of 50 ml of ethyl acetate and 1.1 ml of N-methylmorpholine at 5 °C. Slowly 1.1 ml of ethyl chloroformate was added dropwise to the above solution. The reaction mixture was stirred at the same temperature for 30 minutes. After completion of the reaction, insoluble impurities were removed by filtration. The filtrate was washed with 50 ml of water and the organic phase was separated and dried with anhydrous magnesium sulfate. The dried organic phase was concentrated under reduced pressure to give the crude product. The crude product was purified by silica gel column chromatography (Merck Geduran silica gel, 40-63 μm) with dichloromethane/ethyl acetate (66/34, v/v) as eluent. Finally, 16.9 g of pure product was obtained in 50% yield. Mass spectrometry results: m/z = 170.1 (ES+), theoretical molecular weight M = 169.