Boron tribromide → 1-(1-Benzofuran-3-yl)ethan-1-one

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A solution of 2-methoxyphenylacetone (5 g, 30.5 mmol) in N,N-dimethylformamide dimethyl acetal (8.7 ml, 73.1 mmol) was stirred at 80° C. for 4 hours. The mixture was concentrated under vacuum. The resulting residue was dissolved in dichloromethane (40 ml), cooled to 0° C. and treated with a solution of boron tribromide (5 ml, 52.9 mmol) in dichloromethane (10 ml). After stirring at 0° C. for 1 hour, additional boron tribromide (5 ml, 52.9 mmol) was added. The mixture was stirred at 0° C. for 10 more minutes and was poured into a mixture of ice and saturated aqueous sodium bicarbonate. The resulting mixture was extracted with dichloromethane three times. The combined organic extracts were washed with water once and dried over anhydrous sodium sulfate to give 3-acetylbenzofuran (4.7 g, 96%, 94.5% AUC HPLC): 1H NMR (300 MHz, CDCl3) δ 8.16-8.19 (m, 2H), 7.44-7.48 (m, 1H), 7.29-7.32 (m, 2H), 2.50 (s, 3H).

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