2,1,3-Benzothiadiazole → 3,6-Dibromobenzene-1,2-diamine

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4,7-dibromobenzo[1,2,5]thiadiazole (6.0 g, 20.3 mmol), prepared according to WO 00/55927 PCT/GB00/00911 by bromination of benzo[1,2,5]thiadiazole, was placed in a 200-mL flask under a nitrogen atmosphere. Zinc dust (13.2 g, 203 mmol) and a mixture of acetic acid/water (35 mL/35 mL) were added. The flask was loosely capped with an inverted 1-neck flask. The reaction mixture was heated to 70° C. for 1 hr at which time reaction was complete as determined by TLC. The mixture was then cooled to room temperature and filtered. The solid was extracted with diethylether (3×100 mL). The extract was washed with saturated aqueous sodium bicarbonate and dried over MgSO4. The solution was filtered and evaporated to dryness using a rotary evaporator. The solid was purified by chromatography on a silica gel column, using dichloromethane as eluent. The appropriate fractions were combined and the solvent was removed under reducing pressure. A light yellow product was obtained. Yield: 70%.

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