Step 1. To a stirred solution of 2-bromo-5-chlorobenzoic acid (11 g, 46.7 mmol, HPLC retention time = 2.99 min) in methanol (250 mL) at 0 °C was passed dry HCl gas. The reaction mixture was gradually warmed to room temperature and stirred overnight. Upon completion of the reaction, the mixture was concentrated under reduced pressure to give an orange colored oil. The oily substance was purified by fast column chromatography using hexane as eluent to afford methyl 2-bromo-5-chlorobenzoate as a colorless oil (10.7 g, 92% yield). Thin-layer chromatography (TLC) Rf = 0.6 (5% ethyl acetate-hexane); high-performance liquid chromatography (HPLC) retention time = 3.48 min (Method A); 1H NMR (CDCl3, 400 MHz) δ 7.78 (d, 1H, J = 2.6 Hz), 7.59 (d, 1H, J = 12.8 Hz), 7.30 (dd, 1H, J = 8.6, 2.5Hz), 3.94 (s, 3H).
