GENERAL STEPS: To a suspension of 4,7-dibromo-2,1,3-benzothiadiazole (1) (5.88 g, 20 mmol) in ethanol (190 mL) was added sodium borohydride (14 g, 0.37 mol) in batches at 0 °C. The reaction mixture was stirred at room temperature for 20 hours. Upon completion of the reaction, the volatile solvent was evaporated and water (200 mL) was added, followed by extraction with dichloromethane (3 x 30 mL). The organic phases were combined, dried over anhydrous magnesium sulfate and concentrated under reduced pressure to afford 3,6-dibromo-1,2-benzenediamine (2) (4.7 g, 87% yield) as a light yellow solid. Intermediate 2 was used directly in the next reaction without further purification. Selenium dioxide (1.17 g, 10.5 mmol) was dissolved in hot water (22 mL) and this solution was added to a refluxing ethanol (55 mL) solution of intermediate 2 (2.7 g, 10 mmol). The reaction mixture was heated to reflux for 2 hours. After cooling to room temperature, the precipitate was collected by filtration and recrystallized from ethyl acetate to give 4,7-dibromo-2,1,3-benzoselenadiazole (3) (2.8 g, 80% yield) as golden-yellow needle-like crystals.1H NMR (400 MHz, CDCl3) δ (ppm): 7.65 (s, 2H). Melting point 285-287°C. 13C NMR (100 MHz, CDCl3) δ (ppm): 157.2, 132.1, 116.5. Elemental analysis (C6H2Br2N2Se) Calculated value: C, 21.14; H, 0.59; N, 8.22. Measured value: C, 21.34; H, 0.92; N, 7.98.
