[Cl-].[Cl-].[Cl-].[Al+3].C(Cl)(=O)C(Cl)=O.[CH3:11][C:12]1[O:13][C:14]2[CH:20]=[C:19]([O:21]C(=O)C)[CH:18]=[CH:17][C:15]=2[CH:16]=1.[C:25](=O)([O-:27])[O-:26].[K+].[K+]>ClCCl>[OH:21][C:19]1[CH:18]=[CH:17][C:15]2[C:16]([C:25]([OH:27])=[O:26])=[C:12]([CH3:11])[O:13][C:14]=2[CH:20]=1To a slurry of aluminum trichloride (20.0 g, 150 mmol) in dichloromethane (200 mL) is added oxalyl chloride (13.0 mL, 150 mmol) and the mixture is stirred at 0° C. for 30 minutes. A solution of acetic acid 2-methyl-benzofuran-6-yl ester (9.50 g; 49.9 mmol) in dichloromethane (50 mL) is added over 10 minutes. The ice-bath is removed and the reaction is stirred at room temperature for 2 hours. The reaction mixture is cooled to 0° C. and quenched with MeOH (50 mL). The mixture is concentrated to a residue, dissolved in methanol (250 mL), and treated with potassium carbonate (8.28 g, 59.9 mmol). The mixture is stirred at room temperature for 16 hours, filtered through a pad of celite, and concentrated. The residue is diluted with water (100 mL) and extracted with EtOAc (250 mL×2). The combined organic layers are dried over Na2SO4, filtered, and concentrated. The crude product is purified by flash chromatography (eluted with 25% EtOAc/Hexanes), and the appropriate fractions are concentrated. The material is dried in vacuo to afford 6-hydroxy-2-methyl-benzofuran-3-carboxylic acid (9.56 g, 93%). ES/MS m/e 207.0 (M+1); 205.0 (M−1).
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