[CH3:1][C:2]1[CH:10]=[C:9]([CH3:11])[C:8]([C:12](=[O:15])[CH2:13][CH3:14])=[CH:7][C:3]=1[C:4]([OH:6])=[O:5].S(=O)(=O)(O)O.[CH3:21]O>>[CH3:1][C:2]1[CH:10]=[C:9]([CH3:11])[C:8]([C:12](=[O:15])[CH2:13][CH3:14])=[CH:7][C:3]=1[C:4]([O:6][CH3:21])=[O:5]To a 100-mL round-bottom flask, was carefully added 2,4-dimethyl-5-propionylbenzoic acid (compound 1.4, 1.2 g, 5.8 mmol), sulfuric acid (1.0 mL, 19 mmol) and methanol (30 mL). The resulting solution was stirred at 70° C. for 5 h, then concentrated under reduced pressure. The residue was carefully diluted with H2O (50 mL) and extracted ethyl acetate (100 mL). The organic layer was washed with H2O (2×100 mL) and brine (100 mL), dried (Na2SO4), filtered, and concentrated under reduced pressure. The residue was purified by silica gel column chromatography with ethyl acetate/petroleum ether (1:100) as the eluent to yield the title compound as a light yellow solid (0.90 g, 70%).
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