[Synthesis]
GENERAL STEPS: POCl3 (67.43 mmol) was slowly added dropwise to a stirring 40 cm3 N,N-dimethylformamide (DMF) solution at 0-5 °C for 15 min. The reaction mixture was continued to be stirred at the same temperature for 30 min. Subsequently, 5-nitroindazole (10 g, 61.3 mmol) was dissolved in 10 cm3 DMF and slowly added dropwise at 0-5 °C to the Vilsmeier reagent prepared above. The reaction mixture was then allowed to stand for 3 h at room temperature. Completion of the reaction was confirmed by high performance liquid chromatography (HPLC) monitoring. The reaction mixture was slowly poured into crushed ice and the pH was adjusted by addition of NaOH solution.The precipitated yellow solid was collected by filtration and purified by recrystallization from hot ethanol. The yellow solid product was obtained in 92% yield (10.77 g) with a melting point of 215-217 °C. Infrared spectrum (IR, pure): 3545, 1624, 1537, 1488, 1337, 949, 786, 744 cm?1. 1H NMR (DMSO-d6, 400 MHz): δ = 13.74 (broad single peak, 1H, NH), 8.84 (single peak, 1H), 8.41 (single peak, 1H), 8.21-8.18 (double peak) , 1H, J = 10.4 Hz), 7.74-7.72 (double peak, 1H, J = 9.2 Hz) ppm. 13C NMR (DMSO-d6, 100 MHz): δ = 110, 118, 120, 121, 136, 141, 168 ppm. mass spectrum (ESI): m/z = 192 ([M + H]?) . |