General procedure for the synthesis of 1-(difluoromethyl)-4-nitro-1H-pyrazole from 4-nitropyrazole and sodium difluorochloroacetate: 4-nitro-1H-pyrazole (5.00 g, 44.2 mmol) was added by suspending cesium carbonate (Cs2CO3, 14.41 g, 44.2 mmol) in N,N-dimethylformamide (DMF, 40 mL). The mixture was heated to 120 °C and held for 5 min, followed by addition of solid sodium 2-chloro-2,2-difluoroacetate (13.48 g, 88 mmol) in 10 portions over 20 min. Heating was continued for 10 min and the reaction was completed. The reaction mixture was transferred to a partition funnel containing 100 mL of water and extracted with ether (Et2O, 2 x 50 mL). The organic layers were combined and concentrated. The crude product was purified by normal-phase chromatography using a gradient elution with hexane/ethyl acetate (EtOAc) to afford 1-(difluoromethyl)-4-nitro-1H-pyrazole (6.99 g, 42.9 mmol, 97% yield) as a clear, colorless oil.1H NMR (500 MHz, CDCl3) δ 8.58 (s, 1H), 8.22 (s, 1H) 7.39-7.05 (t, J = 60 Hz, 1H).
