C([O:5][C:6]([C:8]1[O:9][C:10]2[CH:17]=[CH:16][CH:15]=[C:14]([O:18][CH3:19])[C:11]=2[C:12]=1[CH3:13])=[O:7])(C)(C)C.[C:20](Cl)(=[O:22])[CH3:21]>ClC1C=CC=CC=1.[Ti](Cl)(Cl)(Cl)Cl>[C:20]([C:15]1[CH:16]=[CH:17][C:10]2[O:9][C:8]([C:6]([OH:5])=[O:7])=[C:12]([CH3:13])[C:11]=2[C:14]=1[O:18][CH3:19])(=[O:22])[CH3:21]To 4-methoxy-3-methyl-benzofuran-2-carboxylic acid tert-butyl ester (310 mg, 1.18 mmol) dissolved in 9 mL of chlorobenzene was added acetyl chloride (0.3 mL, 3.6 eq). The solution was cooled to <0° C. while titanium tetrachloride (0.61 mL, 4.8 eq) was added dropwise. The reaction mixture was stirred at 0° C. and below for 6 h and then heated in an 85° C. oil bath for 3.5 h. The reaction mixture was poured into ice/water, and the mixture was extracted with ethyl acetate. The combined organic solution was washed with 2N HCl and water. Removal of the solvents gave 167 mg (57% yield) of 5-acetyl-4-methoxy-3-methyl-benzofuran-2-carboxylic acid.
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