3-Acetamido-4-nitrophthalic anhydride (1.3 g, 5.0 mmol) and 4fluororesorcinol (1.3 g, 10 mmol) were added to methanesulfonic acid (10 ml), and the mixture was stirred at 80° C. under an argon atmosphere for 60 hours. The reaction mixture was added with water (120 ml) and refluxed for 2 hours. The reaction mixture was adjusted to pH 2, and precipitates were collected by filtration. The obtained product was dried and purified by silica gel chromatography (3% methanol/97% dichloromethane, v/v) to obtain the title compound (1.3 g, 61%).
