73981-23-4

Ethyl 2-((dimethylamino)methylene)-3-oxovalerate (13.9 mmol, 2.76 g) was used as a raw material and reacted with hydrazine (13.9 mmol, 0.44 mL) in ethanol (50 mL) with stirring for 1 h at room temperature. After completion of the reaction, the solvent was removed by evaporation to obtain the crude product. The crude product was purified by rapid chromatography on silica gel using cyclohexane/ethyl acetate (80:20) as eluent. After purification, the eluent was evaporated to afford ethyl 3-ethyl-1H-pyrazole-4-carboxylate (6.00 mmol, 1.01 g, 43% yield) as a yellow oil. The product was analyzed by liquid chromatography (Zorbax SB-C18, 3.5 μm, 4.6 × 50 mm column): retention time (RT) = 1.53 min; mass spectrum (MS) m/z ES+ = 169.

[1] Patent: WO2009/10455, 2009, A2. Location in patent: Page/Page column 62-63
[2] Patent: US2010/144756, 2010, A1. Location in patent: Page/Page column 25