Step 1: Synthesis of 2,4-difluoro-5-nitroaniline (71)
At 0 °C, 2,4-difluoroaniline (0.394 mL, 3.87 mmol) was dissolved in concentrated sulfuric acid (5 mL, 94 mmol). Nitric acid (0.272 mL, 375 mg, 3.87 mmol) was added slowly and dropwise over 20 min. The reaction mixture was continued to be stirred at 5 °C for 30 min. Subsequently, the reaction mixture was poured into ice water and extracted with ether. The organic layer was washed with saturated NaHCO3 solution and after drying and evaporating the solvent, the target compound 2,4-difluoro-5-nitroaniline (71) was obtained (467 mg, 69.3% yield).
NMR data (400 MHz, CDCl3): δ 3.91 (broad peak, 2H), 6.98 (triple peak, J = 10.2 Hz, 1H), 7.51 (double double peaks, J = 8.6 Hz and 7.0 Hz, 1H).
