General procedure for the synthesis of ethyl 4-bromo-2,3-dihydroxybenzoate from ethanol and 4-bromo-2,3-dihydroxybenzoic acid: 4-bromo-2,3-dihydroxybenzoic acid (3.3 g, 14.0 mmol) was dissolved in ethanol (100 mL), concentrated sulfuric acid (5.0 mL) was added, and the reaction was carried out by heating and refluxing the mixture for 16 hours. After completion of the reaction, the solvent was removed by distillation under reduced pressure. The residue was dissolved in ethyl acetate and washed with water, saturated aqueous sodium bicarbonate and brine in that order. The solvent was again removed by distillation under reduced pressure to give ethyl 4-bromo-2,3-dihydroxybenzoate (3.5 g, 95% yield) as a yellow solid. The product was characterized by 1H NMR (400 MHz, CDCl3): δ 11.14 (s, 1H), 7.20 (d, 1H), 6.96 (d, 1H), 5.93 (br, 1H), 4.34 (q, 2H), 1.34 (t, 3H).
