[Synthesis]
2-Phenylpyrazolo[1,5-a]pyridine-3-carboxylate (12.0 g) was used as raw material and dissolved in 238 mL of methanol. Under argon protection and ice bath cooling conditions, 2 mol/L aqueous potassium hydroxide solution (119 mL) was slowly added to the solution. The reaction mixture was warmed up to 80°C with continuous stirring for 5 hours. Upon completion of the reaction, 2 mol/L aqueous hydrochloric acid (480 mL) was added to the reaction solution for acidification and a solid was precipitated. The precipitate was collected by filtration and dried under vacuum to afford the target product 2-phenylpyrazolo[1,5-a]pyridine-3-carboxylic acid as an orange solid (10.2 g). The product was characterized by 1H-NMR (400 MHz, DMSO-d6): δ 7.15 (1H, td, J=6.7,1.4 Hz), 7.42-7.46 (3H, m), 7.55-7.58 (1H, m), 7.74-7.77 (2H, m), 8.15 (1H, d, J=4.5 Hz), 8.84 (1H, d. J=6.8Hz). |