[Br:1][C:2]1[CH:10]=[CH:9][C:5]([C:6]([OH:8])=[O:7])=[C:4]([CH3:11])[CH:3]=1.S(=O)(=O)(O)O.O.[CH:18]1[CH:23]=CC=C[CH:19]=1>C(O)(C)C>[CH:18]([O:7][C:6](=[O:8])[C:5]1[CH:9]=[CH:10][C:2]([Br:1])=[CH:3][C:4]=1[CH3:11])([CH3:23])[CH3:19]A solution of 4-bromo-2-methyl-benzoic acid (Aldrich, 5.4 g, 25 mmol) in benzene (75 mL) and isopropanol (75 mL) was treated with concentrated sulfuric acid (1.5 mL) and heated to reflux over 4 days using a Dean-Stark water trap. The volatiles were evaporated in vacuo, the residue was diluted with water and extracted with diethyl ether. The organic phase was washed with water and saturated, aqueous sodium bicarbonate solution, dried over anhydrous magnesium sulfate, filtered and evaporated in vacuo to afford the title product as a clear oil that was used as such for the next step (6.12 g, 95%).
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