[CH3:1][C:2]1[C:10]([CH3:11])=[CH:9][CH:8]=[CH:7][C:3]=1[C:4]([OH:6])=[O:5].[N+]([O-])(O)=O.[Br:16]Br>C(O)(=O)C.O.[N+]([O-])([O-])=O.[Ag+]>[Br:16][C:8]1[CH:9]=[C:10]([CH3:11])[C:2]([CH3:1])=[C:3]([CH:7]=1)[C:4]([OH:6])=[O:5]To a solution of 2,3-dimethylbenzoic acid (5 g, 33.3 mmol, 1.0 eq) in acetic acid (167 mL) at room temperature was added a solution of conc. nitric acid (25.2 g, 399 mmol, 12 eq), water (15 g, 0.83 mmol, 25 eq) and bromine (5.85 g, 36.6 mmol, 1.1 eq). A solution of silver nitrate (7.35 g, 43 mmol, 1.3 eq) in water (43 mL) was then added dropwise over 30 min. Once addition was completed, the reaction was stirred at room temperature for 1 h, then quenched by addition of water and EtOAc. The aqueous layer was extracted with EtOAc and the combined organic extracts were washed with water and brine, dried (Na2SO4), filtered and evaporated in vacuo to give the title compound as a yellow solid (6.4 g, 83%).
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