General procedure for the synthesis of 4-fluoro-7-nitro-2,1,3-benzoxadiazole from 4-fluoro-2,1,3-benzoxadiazole: 4-fluoro-2,1,3-benzoxadiazole (1.00 g, 7.24 mmol) was dissolved in concentrated H2SO4 (8 mL) and cooled to -10 °C. The nitration mixture (H2SO4:HNO3, 3:1, 2.40 mL) was added slowly and dropwise with stirring. The reaction temperature was maintained at -10 °C and stirring was continued for 1 hour. The progress of the reaction was monitored by TLC and LCMS. Upon completion of the reaction, the reaction mixture was quenched with H2O (250 mL) and extracted with EtOAc (2 x 250 mL). The organic layers were combined, dried with anhydrous Na2SO4 and concentrated under reduced pressure. The crude product was purified by fast column chromatography (eluent: 0 to 10% EtOAc gradient in hexane) to afford 4-fluoro-7-nitro-2,1,3-benzoxadiazole (0.39 g, yellow solid) in 30% yield.1H NMR (400 MHz, DMSO-d6) δ 7.70 (d, J=8.40 Hz, 1H), 8.77-8.80 (m 1H).
