3.2.4. Synthesis of 1H-Indole-2-Carbohydrazide (6)

To a stirred solution of ethyl 1H-indole-2-carboxylate (5) (0.46 g, 7.93 mmol) was added hydrazine monohydrate (4 mL, 79.90 mmol) in the presence of 15 mL of absolute ethanol. The reaction mixture was refluxed for 6 h. After the reaction was complete, the solution was evaporated under vacuum, the remaining residue after evaporation (0.50 g) was washed with dichloromethane (0.5 mL × 3). The product was obtained as colorless crystals and was used directly in the following reaction without any further purifications [66]. M.p. 245–246 °C (Lit. M.p. 247–248 °C), ¹H-NMR (DMSO-d₆): δ 4.49 (s, 2H, NH₂), 7.13 (d, J = 4.6 Hz, 1H, Ar), 7.19 (s, 1H, Ar), 7.25 (d, J = 7.4 Hz, 1H, Ar), 7.49 (d, J = 7.4 Hz, 1H, Ar), 7.65 (d, J = 7.5 Hz, 1H, Ar), 9.79 (s, 1H, NH), 11.68 (s, 1H, NH, indole).