3-Methyl-but-2-enoic acid 4-bromo-phenyl ester → 2H-1-Benzopyran-2-one, 6-bromo-3,4-dihydro-4,4-dimethyl-

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A solution of 3-methyl-but-2-enoic acid 4-bromo-phenyl ester (7 g, 27.6 mmol) in anhydrous dichloromethane (200 mL) was cooled (ice bath) and treated with aluminum chloride (6.6 g, 49.6 mmol) and the reaction mixture was stirred overnight at ambient temperature. The reaction mixture was quenched with saturated aqueous sodium bicarbonate solution and extracted with diethyl ether (×2). The combined organic extract was washed woth brine (×1), dried over anhydrous sodium sulfate, filtered and evaporated in vacuo to afford an oil which was purified by flash column chromatography over silica gel (230-400 mesh) using 2.5% ethyl acetate in hexane as the eluent to afford the title compound (4.2 g, 57%).

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