General procedure for the synthesis of 2-amino-3,4-dichlorobenzoic acid from 6,7-dichloroindole-2,3-dione: 6,7-dichloroindole-2,3-dione (1 g, 4.6 mmol) was added to an aqueous (10.5 mL) suspension of potassium hydroxide (370 mg, 6.6 mmol) and potassium chloride (920 mg, 12.3 mmol) cooled to 0 °C . Subsequently, a 30 wt% aqueous hydrogen peroxide solution (1.1 mL, 35 mmol) was added slowly and dropwise. The reaction mixture was stirred at room temperature for 30 min, then ethyl acetate (4.0 mL) was added. The resulting mixture was washed sequentially with water, the organic layer was separated and dried over anhydrous sodium sulfate. Decarboxylation product (910 mg, 95% yield) was obtained after concentration under reduced pressure. The structure of the product was confirmed by 1H NMR (400 MHz, DMSO-d6): δ 13.16 (s, 1H), 7.73 (d, J = 8.6 Hz, 1H), 7.11 (s, 2H), 6.81 (d, J = 8.6 Hz, 1H).
