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

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A mixture of 1-(2-methoxyphenyl)propan-2-one (77.2 g) and dimethylformamide dimethyl acetal (137.5 g) was stirred at 80° C. under nitrogen for 4 hours, then concentrated in vacuo to leave a viscous oil. The oil was dissolved in dichloromethane (620 ml) then the stirred solution was cooled to 0° C. Boron tribromide (1M solution in dichloromethane, 800 ml) was added dropwise over 1.75 hours at 0°-5° C., then the mixture was stirred at 0°-5° C. for a further 1.5 hours and poured onto an excess of ice and saturated aqueous sodium hydrogen carbonate solution. Solid sodium hydrogen carbonate was added in portions with occasional stirring until effervescence ceased. The product was extracted into dichloromethane (3×600 ml) then the combined extracts were washed with water (2×600 ml), dried (Na2SO4), and the solvent removed in vacuo to leave 3-acetylbenzo[b]furan as a brown oil (78.9 g).

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