4027-57-0

3273-44-7

General procedure for the synthesis of 5-methyl-1H-pyrazole-3-carbaldehyde from ethyl 3-methylpyrazole-5-carboxylate: 3-ethoxycarbonyl-5-methylpyrazole (1.0 g, 4.34 mmol) was dissolved in 15 ml of purified toluene under the protection of nitrogen, diisobutylaluminum hydride (DIBAL, 8.68 ml, 8.62 mmol) was added slowly and the reaction was carried out at -78 C. The reaction was stirred. The progress of the reaction was monitored by thin layer chromatography (TLC, unfolding agent ratio hexane: ethyl acetate = 6:1). Upon completion of the reaction, the reaction was quenched by slow addition of methanol and water and the resulting mixture was filtered through a bed of diatomaceous earth and the aqueous layer was extracted with ethyl acetate (EtOAc). The organic layers were combined, dried with anhydrous magnesium sulfate (MgSO4), filtered and concentrated under reduced pressure. The concentrate was purified by column chromatography (eluent ratio of hexane: ethyl acetate: dichloromethane = 3:1:1) to afford the target product 5-methyl-1H-pyrazole-3-carbaldehyde in 82.4% yield. The structure of the product was confirmed by 1H NMR (300 MHz, CDCl3): δ 9.92 (s, 1H), 6.68 (s, 1H), 2.82 (s, 3H).