General procedure for the synthesis of 5-formyl-2-thiophenecarboxylic acid from methyl 5-formylthiophene-2-carboxylate: the compound methyl 5-formylthiophene-2-carboxylic acid (2 g, 12.8 mmol) was dissolved in 200 mL of a mixed solvent (THF:H2O = 1:1), and the hydrolysis reaction was carried out by adding KOH (1.1 g, 19.2 mmol). Upon completion of the reaction, THF was removed by distillation under reduced pressure.Subsequently, the pH of the aqueous layer was adjusted to 1-2 with 1N HCl solution and extracted with ethyl acetate (200 mL × 5), resulting in the target compound 5-formyl-2-thiophenecarboxylic acid (1.2 g, 59% yield).1H NMR (300 MHz, CDCl3) δ 10.00 (s, 1H), 7.93- 7.92 (d, J = 3.92 Hz, 1H), 7.78-7.77 (d, J = 3.9 Hz, 1H).13C NMR (300 MHz, CDCl3) δ 182.2, 163.30, 141.57, 139.70, 133.79, 132.
