General procedure for the synthesis of 3-amino-5-benzyl-1H-pyrazole from 3-oxo-4-phenylbutanenitrile: A mixed solution of 3-oxo-4-phenylbutanenitrile (Method 26; 0.58 g, 3.64 mmol) with hydrazine monohydrate (0.177 mL, 3.64 mmol) in ethanol (16 mL) was heated and refluxed for 3 hours. Upon completion of the reaction, the mixture was cooled to 25 °C and subsequently concentrated under reduced pressure. The reaction mixture was extracted with dichloromethane (15 mL) and washed twice with saturated saline. The organic layer was dried over anhydrous sodium sulfate and concentrated under reduced pressure to give an orange solid. The solid was ground with a mixture of hexane and ether (1:1) and collected by filtration to afford 3-amino-5-benzyl-1H-pyrazole as a yellow solid (0.38 g, 60% yield).1H NMR (400 MHz, CDCl3) δ 3.9 (s, 2H), 4.89 (br s, 1H), 5.44 (s, 1H), 7.19-7.34 (m 5H). Mass spectrum (MS): calculated value: 173; measured value: [M + H]+ 174.
