a) Under argon protection, 4-nitro-1H-pyrazole (283 mg, 2.5 mmol) was dissolved in anhydrous DMF (5 mL), followed by the addition of NaH (120 mg, 2.75 mmol). The reaction mixture was stirred at 0 °C for 1 h, then cooled to 0 °C again and benzyl bromide (300 μL, 2.5 mmol) was added dropwise. Subsequently, the reaction mixture was stirred at room temperature for 12 hours. After completion of the reaction, the reaction mixture was diluted with water and extracted with ethyl acetate. The organic phases were combined and purified by silica gel column chromatography using heptane/ethyl acetate as eluent. The final product was 1-benzyl-4-nitro-1H-pyrazole as a light yellow oil (484 mg, 95% yield). Mass spectral analysis (ISP, m/e): 226.3 (100) [(M + Na)+].
