General procedure for the synthesis of 3-bromo-6-fluoro-2-methylbenzoic acid from 2-fluoro-6-methylbenzoic acid: 2-fluoro-6-methylbenzoic acid (1.48 g, 9.60 mmol) was dissolved in a mixture of concentrated hydrochloric and sulfuric acids (40 mL) at 0 °C. Subsequently, N-bromosuccinimide (NBS, 1.79 g, 10.1 mmol) was added to this solution. The reaction mixture was stirred continuously at 0 °C for 3 hours. After completion of the reaction, the mixture was poured into ice water (200 mL) and extracted with ether (2 x 200 mL). The organic phases were combined, dried with anhydrous sodium sulfate and subsequently concentrated under reduced pressure to afford the target product 3-bromo-6-fluoro-2-methylbenzoic acid (Compound QQ, 2.15 g, 96% yield) as a solid. The structure of the product was confirmed by 1H NMR (400 MHz, chloroform-d): δ 7.64 (dd, J = 8.84,5.31 Hz, 1H), 6.92 (t, J = 8.84 Hz, 1H), 2.54 (s, 3H); mass spectrometry (MS) showed the molecular ion peak [M + H]+ as 231.0.
