Step 1 Synthesis of 6-chloro-1H-benzo[d][1,3]oxazine-2,4-dione: 2-Amino-5-chlorobenzoic acid (17 g, 0.1 mol) and 1,2-dichloroethane (200 mL) were added to a 500 mL three-necked round-bottom flask. A solution of triphosgene (21 g, 0.21 mol) in 1,2-dichloroethane (100 mL) was slowly added dropwise to the above solution at 80 °C. After the dropwise addition was completed, the reaction mixture was continued to be heated and stirred at 80°C for 3 hours. After completion of the reaction, the mixture was cooled to room temperature in an ice water bath. The precipitated white solid precipitate was collected by filtration and washed with an appropriate solvent and dried to afford 6-chloro-1H-benzo[d][1,3]oxazine-2,4-dione (19 g, 97% yield). The product was characterized by 1H NMR (300 MHz, DMSO-d6): δ 11.85 (br, 1H), 7.88 (d, J = 2.4 Hz, 1H), 7.78 (dd, J = 8.7, 2.4 Hz, 1H), 7.15 (d, J = 8.7 Hz, 1H).
