a) A suspension of 2-bromo-5-fluorophenol (20.0 g, 104.7 mmol) and potassium carbonate (21.71 g, 157.1 mmol) was formed in acetone (200 mL). To this suspension dimethyl sulfate (10.90 mL, 115.2 mmol) was slowly added. The reaction mixture was stirred at 60 °C for 2 h. After completion of the reaction, it was cooled to room temperature and subsequently concentrated under reduced pressure to remove the solvent. The concentrated residue was dissolved in a mixture of ether (200 mL) and water (100 mL) to separate the organic phase. The organic phase was washed sequentially with 2N aqueous hydrochloric acid (50 mL) and saturated sodium bicarbonate solution (50 mL), and then dried with anhydrous magnesium sulfate. The dried organic phase was evaporated from the solvent under reduced pressure to give the light yellow oily product 2-bromo-5-fluoroanisole (21.46 g, 100% yield). The product was confirmed by NMR hydrogen spectrum (300 MHz, CDCl3): δ 7.45 (1H, dd, Ar-H), 6.70-6.55 (2H, m, Ar-H), 3.90 (3H, s, OCH3).
