1H-Pyrazole-3-carboxylicacid,4-formyl-,ethylester(9CI)

68-12-2

14923-66-1

179692-09-2

Example 55B. Synthesis of ethyl 4-formyl-1H-pyrazole-3-carboxylate: Phosphoryl chloride (14.6 g, 95 mmol) was added dropwise to dry N,N-dimethylformamide (15 mL) at 0 °C under argon protection and stirred for 30 min. Subsequently, Example 55A (2.8 g, 16 mmol) was added in batches at 0 °C. The resulting orange solution was slowly warmed to room temperature and stirred at 60 °C for 4 hours. Upon completion of the reaction, the mixture was cooled to room temperature and poured into crushed ice. The pH was adjusted with 3N NaOH solution to about 6. The mixture was heated at 60 °C for 5 min and then cooled to room temperature. After standing at room temperature overnight, the solid was collected by filtration to give the target product Example 55B (1.5 g, 55% yield). The product was analyzed by LC-MS, [M + H]+ = 169. 1H NMR (DMSO-d6, 400 MHz) δ 14.19 (br.s, 1H), 10.26 (s, 1H), 8.43 (br.s, 1H), 4.37 (q, J = 7.2 Hz, 2H), 1.34 (t, J = 7.2 Hz, 3H).