N-(3-bromo-2-fluorophenyl)-2-(hydroxyimino)acetamide (1.82 g, 7.03 mmol) was used as a raw material, which was slowly added to concentrated sulfuric acid (20 mL) at 60°C. Subsequently, the temperature of the reaction system was raised to 90°C and the reaction was maintained at this temperature for 3 hours. Upon completion of the reaction, the mixture was cooled to room temperature and carefully poured into ice water. The precipitated yellow precipitate was collected by filtration and dried to give 6-bromo-7-fluorodihydroindole-2,3-dione (1.41 g, 82% yield). The product was characterized by 1H NMR (400 MHz, DMSO-d6): δ 11.75 (s, 1H), 7.39 (dd, J = 5.7,7.9 Hz, 1H), 7.31 (d, J = 8.2 Hz, 1H).
