General procedure for the synthesis of methyl 3-bromo-5-(bromomethyl)benzoate from methyl 3-bromo-5-(hydroxymethyl)benzoate: methyl 3-bromo-5-(hydroxymethyl)benzoate (2.0 g, 8.2 mmol) was mixed with triphenylphosphine (4.28 g, 16.3 mmol) in tetrahydrofuran (20 mL) and the mixture was cooled down to 0°C. The reaction was completed by the addition of N-bromosuccinimidamide (3.05 g, 17.1 mmol). Subsequently, N-bromosuccinimide (3.05 g, 17.1 mmol) was added in batches and the reaction mixture was allowed to gradually warm up to room temperature. After 16 h of reaction, the reaction mixture was diluted with ethyl acetate, washed sequentially with saturated sodium bicarbonate solution (2×) and brine (2×), the organic phase was dried with anhydrous sodium sulfate and concentrated under reduced pressure. Purification by silica gel column chromatography (eluent: 10% ethyl acetate/hexane) gave 2.1 g of light brown oily product in 83% yield. The product was identified by 1H-NMR (CDCl3, 300 MHz): δ 8.07 (s, 1H), 7.96 (s, 1H), 7.70 (s, 1H), 4.42 (s, 2H), 3.90 (s, 3H). Mass spectrometry analysis showed a molecular ion peak of 308.93 (MH)+.
