General procedure for the synthesis of 4-bromo-6-cyanoquinoline from 4-oxo-1,4-dihydroquinoline-6-carbonitrile: Phosphorus tribromide (8 ml, 84.6 mmol) was added drop-wise to a solution of 4-oxo-1,4-dihydroquinoline-6-carbonitrile (12 g, 70.5 mmol) in N,N-dimethylformamide (DMF, 75 ml) over a period of 5 min, the reaction being The reaction is slightly exothermic. Upon completion of the reaction, the reaction mixture was cooled to room temperature and then diluted with ice water (100 ml) and stirring was continued for 1 hour. Subsequently, the reaction mixture was further diluted with additional water (300 ml). The solid product was collected by filtration, washed with water and dried in air to give 14.3 g of the target product in 87% yield. Mass spectrum (positive ion electrospray) m/z 233 (MH+).
