Ammonia → Ethyl 3-(7-ethyl-4-oxo-4,5-dihydropyrrolo[1,2-a]quinoxalin-1-yl)propanoate

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4-Ethyl-2-nitroaniline 1.00 g, ethyl 6-(1,3-dioxolan-2-yl)-4-oxohexanoate 1.38 g, p-toluenesulfonic acid monohydride 114 mg and toluene 150 mL were mixed and heated under reflux for 70 hours with Dean-Stark device, and thereafter the solvent was distilled off under reduced pressure. The residue was subjected to silica gel chromatography (chloroform) to provide 1.29 g of a brown, viscous substance, to which 20 mL of acetic acid and 8 mL of water were added, followed by addition of 2.35 g of sodium hyposulfite and 3 hours' heating under reflux. The reaction liquid was allowed to cool off, to which 50 g of ice was added and it was made weakly alkaline with 25% aqueous ammonia, and extracted with ethyl acetate. The organic layer was washed with 20 mL of saturated brine, dried over anhydrous magnesium sulfate and from which the solvent was distilled off under reduced pressure. The residue was purified on silica gel chromatography (hexane:ethyl acetate=1:1) to provide 471 mg of a brown, viscous substance. It was mixed with 178 mg of triphosgene and 10 mL of toluene, and heated under reflux for 14.5 hours. Cooling the reaction liquid off, the precipitate was recovered by filtration, washed with ethyl acetate and dried under reduced pressure to provide 277 mg of the title compound.

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