[CH2:1]([O:8][C:9]1[CH:15]=[C:14]([Br:16])[CH:13]=[C:12]([N+:17]([O-:19])=[O:18])[C:10]=1[NH2:11])[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.[C:20](OC(=O)C)(=[O:22])[CH3:21].O>C(O)(=O)C.S(=O)(=O)(O)O>[CH2:1]([O:8][C:9]1[CH:15]=[C:14]([Br:16])[CH:13]=[C:12]([N+:17]([O-:19])=[O:18])[C:10]=1[NH:11][C:20](=[O:22])[CH3:21])[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1To a solution of 2-(benzyloxy)-4-bromo-6-nitroaniline (33.0 g, 102 mmol, WO 2004054984) and acetic anhydride (14.5 mL, 153 mmol) in acetic acid (90 mL) was added concentrated sulfuric acid (2 drops) at 70° C. The mixture was stirred at 70° C. for 20 minutes. After cooling to room temperature, water (800 mL) was added, and the formed precipitate was collected by filtration and washed with diisopropyl ether to afford the title compound as a brown solid (30.9 g, 83%).
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