(1) Under nitrogen protection, 2,5-dibromonitrobenzene (14.1 g, 50 mmol) was dissolved in 55 mL of N,N-dimethylformamide with copper powder (7.0 g, 109 mmol), and the reaction was stirred for 1 hour at 125°C. After completion of the reaction, the reaction was cooled to room temperature, the reaction mixture was filtered, and the solid residue was washed with an appropriate amount of toluene to ensure that the target product, 4,4'-dibromo-2,2'-dinitrobiphenyl, was dissolved in the filtrate. The filtrate was distilled under reduced pressure to give the crude product. The crude product was purified by silica gel column chromatography and separated under reduced pressure with petroleum ether and dichloromethane (4:1, v/v) as eluent to give a yellow solid product in 91% yield. The product was characterized by 1H NMR and confirmed to be 4,4'-dibromo-2,2'-dinitrobiphenyl.
