2-Amino-4-fluorobenzamide → 7-Fluoro-3,4-dihydro-1,2,3-benzotriazin-4-one

59.23 g (0.387 mol) of benzotriazol-1-ol, 65.776 ml (0.387 mol) of N-ethyldiisopropylamine and 74.15 g (0.387 mol) of N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride were added successively at room temperature to a solution of 50.0 g (0.322 mol) of 2-amino-4-fluorobenzoic acid in 600 ml of dimethylformamide. 64.46 ml (0.451 mol) of ammonia in methanol (7 mol/l) were added dropwise with stirring, and the mixture was stirred for 18 hours. Water (2 l) and concentrated sodium chloride solution (0.5 l) were added to the batch. The mixture was extracted three times with ethyl acetate (0.75 l each time). The organic phase was dried over sodium sulfate, filtered, and the solvent was subsequently stripped off in a Rotavapor. The residue was triturated with 2-methoxy-2-methylpropane (0.2 l) and ligroin (0.1 l). The crystalline precipitate was filtered off with suction and dried in a drying cabinet, giving 44.5 g of 2-amino-4-fluorobenzamide as solid. 35.85 g (0.520 mol) of sodium nitrite in 75 ml of water were added dropwise at room temperature to a suspension of 44.5 g (0.289 mol) of 2-amino-4-fluorobenzamide in 1.4 l of hydrochloric acid (25%). The mixture was stirred for 2 hours with ice-cooling. The deposited precipitate was filtered off with suction, rinsed with water and dried at 60° C. in a vacuum drying cabinet, giving 32.58 g of 7-fluoro-3H-benzo[d]-1,2,3-triazin-4-one as solid; HPLC/MS (M+H)+=166; 1H NMR (300 MHz, DMSO) δ 8.32 (dd, J=8.8, 5.7, 1H), 7.87 (dd, J=9.0, 2.5, 1H), 7.64 (td, J=8.7, 2.5, 1H).