[Synthesis]
Step 1: 3,5-dibromoaniline (5.00 g, 19.9 mmol), sodium 3-nitrobenzenesulfonate (987 mg, 4.39 mmol), ferrous sulfate heptahydrate (63.2 mg, 0.658 mmol) and methanesulfonic acid (20 mL) were added to a 100 mL round-bottom flask. A reflux condenser tube was installed and the reaction system was heated in an aluminum bath at 120 °C. Glycerol (0.64 mL, 8.8 mmol) was added slowly and dropwise through the condenser tube, followed by raising the temperature of the aluminum bath to 130 °C. The reaction mixture was stirred continuously at 130 °C overnight. Upon completion of the reaction, it was cooled to room temperature, diluted with dichloromethane and water, cooled in an ice-water bath, and the pH was adjusted to alkaline by slowly adding 50% aqueous sodium hydroxide. The mixture was filtered through Celite and extracted with dichloromethane. The organic phases were combined, dried over anhydrous sodium sulfate and concentrated under reduced pressure to give a brown solid. Purification by silica gel column chromatography (80 g silica gel, elution gradient: 0 to 60% ethyl acetate/heptane, 17 column volumes, followed by maintaining 40% ethyl acetate/heptane) afforded 5,7-dibromoquinoline as a brown solid (3.19 g, 56% yield). The structure of the product was confirmed by 1H NMR (400 MHz, CDCl3): δ 7.53 (dd, 1H), 7.96 (d, 1H), 8.29 (d, 1H), 8.50 (d, 1H), 8.93 (dd, 1H). lC-MS (ESI) m/z: 285.9 [M + H]+ (95% purity).LC-MS data were obtained after reaction of the mixtures were obtained immediately after treatment. |