43024-15-3

43024-14-2

43024-15-3

The general procedure for the synthesis of 4-ethyl-1H-pyrazol-3-amine from 2-formylbutanenitrile was as follows: potassium tert-butanolate (112.0 g, 1.00 mol) was placed in a 5 L flask fitted with a charging funnel under nitrogen protection, and anhydrous ether (3.0 L) was added and stirred to dissolve. Subsequently, a mixed solution of 2-formylbutanenitrile (69.0 g, 1.00 mol) with methyl acetate (77.7 g, 1.05 mol) was added slowly dropwise over a period of 3 hours. After the dropwise addition was completed, the reaction mixture was stirred at room temperature overnight. After the reaction was complete, the mixture was cooled to 0 °C, neutralized by the addition of acetic acid (57 mL), the reaction mixture was filtered and the solids were washed with ether (500 mL). The filtrates were combined and rotary evaporated at room temperature to give a light yellow oil (95.1 g). This oil was dissolved in anhydrous ethanol (100 mL), 99% hydrazine monohydrate (48 mL) and acetic acid (14 mL) were added sequentially and refluxed overnight under nitrogen protection. At the end of the reaction, the solvent was removed by evaporation and the resulting oil was purified by silica gel column chromatography, using a methanol solution of dichloromethane:7N ammonia as eluent. Finally 22.4 g (20% yield) of 3-amino-4-ethylpyrazole was obtained as a clear oily substance, which solidified on standing.