General procedure for the synthesis of 7-chloro-1H-benzo[d][1,3]oxazine-2,4-dione from triphosgene and 2-amino-4-chlorobenzoic acid:
1. Preparation of Intermediate G: To a stirred solution of 2-amino-4-chlorobenzoic acid (10 g, 0.058 mol) in acetonitrile (60 mL), a solution of pyridine (9.4 mL, 0.117 mol, 2 eq.) and triphosgene (17.3 g, 0.058 mol, 1 eq.) in dichloromethane (85 mL, 0.7 M) was slowly added.
2. Treatment of the reaction mixture: the resulting orange reaction solution was heated at 50 °C for 2 h and subsequently cooled to room temperature.
3. Separation and purification: the reaction solution was diluted with water (50 mL) to separate the organic and aqueous layers. The aqueous layer was extracted with dichloromethane (3 x 50 mL) and the combined organic layers were washed once with brine (50 mL) and dried with anhydrous magnesium sulfate. 4. Purification of products: The reaction solution was heated at 50 °C for 2 h and subsequently cooled to room temperature.
4. Purification of product: The solvent was removed by distillation under reduced pressure to give a yellow solid. The solid was recrystallized from hexane to give 7-chloro-1H-benzo[d][1,3]oxazine-2,4-dione (9.1 g, 74% yield) as a yellow solid.
1H NMR (acetone-d6, 500 MHz): δ (ppm) 7.13-7.14 (1H, s), 7.28-7.30 (1H, d, J = 8.5 Hz), 7.90-7.92 (1H, d, J = 8.6 Hz), 11.84 (1H, bs).
