General procedure for the synthesis of methyl 3-amino-5-chloro-2-hydroxy-2-hydroxybenzoate from methyl 5-chloro-2-hydroxy-3-nitrobenzoate: Methyl 5-chloro-2-hydroxy-3-nitrobenzoate (2.00 g, 10.7 mmol) was dissolved in 6 mL of concentrated sulfuric acid and stirred at 0 °C. Subsequently, a mixture of concentrated sulfuric acid and concentrated nitric acid (1:1, 1.6 mL, v/v) was slowly added, and the reaction mixture was gradually warmed up to room temperature with continuous stirring for 24 hours. After the reaction was completed, the mixture was poured into ice water, the precipitate was collected by filtration, washed with water and dried to obtain the nitro compound. The nitro compound was suspended in a solvent mixture of 15 mL of ethyl acetate and 15 mL of methanol, 5% palladium/carbon catalyst (0.350 g) was added, and the hydrogenation reduction reaction was carried out at room temperature for 4 hours. At the end of the reaction, the catalyst was removed by filtration and the filtrate was concentrated to afford methyl 3-amino-5-chloro-2-hydroxybenzoate solid 1.61 g in 74.6% yield. The product was characterized by 1H-NMR (CDCl3): δ 10.84 (1H, s), 7.20 (1H, d, J=2.4Hz), 6.83 (1H, d, J=2.4Hz), 3.94 (3H, s).
