[Br:1][C:2]1[C:11]([Br:12])=[CH:10][C:5]2[O:6][CH2:7][CH2:8][O:9][C:4]=2[C:3]=1[C:13]([OH:15])=[O:14].C(O)(=O)C.[N+:20]([O-])([OH:22])=[O:21].S(=O)(=O)(O)O>O>[Br:1][C:2]1[C:11]([Br:12])=[C:10]([N+:20]([O-:22])=[O:21])[C:5]2[O:6][CH2:7][CH2:8][O:9][C:4]=2[C:3]=1[C:13]([OH:15])=[O:14]A 20-mL round bottom flask was charged with 6,7-dibromo-2,3-dihydrobenzo[b][1,4]dio-xine-5-carboxylic acid (3.0 g, 0.61 mmol) and acetic acid (2 mL). The mixture was heated to 37° C., following by the addition of a solution of nitric acid (d=1.49, 1.0 mL), acetic acid (1.0 mL) and concentrated sulfuric acid (1.0 mL). After heating at 50° C. for 1 h, the mixture was poured in cold water while stirring. It was then filtered and the solid was washed with water to afforded the title compound (1.91 g, 83%). LCMS: ESI (3 minute run), m/z=382 [M+1]+; Retention time: 1.05 minute.
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