8-Bromo-5-fluoro-2,2-dimethyl-benzo[1,3]dioxin-4-one

3-bromo-6-fluoro-2-hydroxybenzoic acid (25 g, 106.38 mmol, 1 eq) was dissolved in a mixed solution of DMF (1.5 mL) and acetone (63.20 g, 1.09 mol, 80 mL, 10.23 eq). At 0°C, TFAA (151.00 g, 718.94 mmol, 100 mL, 6.76 eq) and TFA (10 mL) were added dropwise to the mixed solution. The temperature of the mixed solution was raised to 100°C and stirred for 12 hours. The mixed solution was poured into saturated Na2CO3(500 mL) and stirred for 10 minutes. Then extract with ethyl acetate (150 mL×2). The combined organic phases were washed with brine (15 mL x 2), dried over anhydrous Na2SO4, filtered, and concentrated in vacuo. The crude product after the residue was purified by column chromatography (SiO2, petroleum ether/ethyl acetate=1/0 to 20/1) was washed with PE (40 mL), filtered and the filter cake was dried under reduced pressure to obtain 8-Bromo-5-fluoro-2,2-dimethyl-benzo[1,3]dioxin-4-one.