General procedure for the synthesis of benzofuran-4-carboxylic acid from methyl benzofuran-4-carboxylate: a solution of LiOH (1.44 g, 34.3 mmol) in water (20 mL) was added to a mixture of THF (20 mL) and MeOH (20 mL) of methyl benzofuran-4-carboxylate (2.02 g, 11.4 mmol) and the reaction was stirred at room temperature for 16 The reaction was stirred for 16 hours at room temperature. After completion of the reaction, the solvent was removed by evaporation. The residue was dissolved in water (50 mL) and acidified with concentrated HCl to pH < 2. The precipitate was collected by filtration and dried to afford benzofuran-4-carboxylic acid (1.83 g, 99% yield). The product was characterized by 1H NMR (DMSO-d6): δ 13.10 (s, 1H), 8.14 (d, J = 2.1 Hz, 1H), 7.85-7.91 (m, 2H), 7.43 (t, J = 7.9 Hz, 1H), 7.33 (dd, J = 2.1, 1.0 Hz, 1H). Mass spectrum measured value: [M-H]? = 161.1.
