General procedure for the synthesis of 7-bromo-4-chloro-3-nitroquinolin-4-ol from 7-bromo-3-nitroquinolin-4-ol: 7-bromo-3-nitroquinolin-4-ol (3.8 g, 14.12 mmol) was suspended in phosphorous trichloride (20 mL) and anhydrous N,N-dimethylformamide (1 mL) was added. The reaction mixture was heated to 120 °C and maintained for 3 h under nitrogen protection. After completion of the reaction, it was cooled to room temperature. The precipitate was collected by filtration, washed with water and subsequently partitioned between dichloromethane (60 mL) and saturated aqueous sodium carbonate solution. The organic layer was separated, washed with saturated saline, dried over anhydrous sodium sulfate, filtered and concentrated to give 7-bromo-4-chloro-3-nitroquinoline (3.3 g, 11.5 mmol, 81%) as a beige solid. Mass spectrum (electrospray ionization, m/z): [M + H]+ = 287.1 / 288.9.
