General procedure for the synthesis of 5-bromo-1,2,3,4-tetrahydroquinoline from 4-bromoinden-1-one: 4-bromoinden-1-one (1.05 g, 5 mmol) was dissolved in methanol (14 ml), hydroxylamine hydrochloride (1.4 g, 20 mmol) was added, and the reaction was carried out at reflux for 1 hour. After completion of the reaction, vacuum concentration was carried out followed by addition of dichloromethane and 50% sodium bicarbonate solution and stirring for 20 min. The organic layer was separated, dried with anhydrous sodium sulfate and concentrated to give a white solid in 99% yield. The white solid (5 mmol) obtained above was dissolved in dichloromethane (30 ml), cooled to 0 °C and diisobutylaluminum hydride (20 ml, 30 mmol, 1.5 M toluene solution) was added slowly. The reaction mixture was stirred at 0°C for 30 min, then moved to room temperature and continued stirring overnight. After completion of the reaction, the reaction was quenched with water under ice bath conditions, extracted with dichloromethane, the organic layer was washed with saturated brine and dried over anhydrous sodium sulfate. After concentration, it was purified by silica gel column chromatography (petroleum ether: ethyl acetate = 3:1) to give 600 mg of 5-bromo-1,2,3,4-tetrahydroquinoline as a pale yellow solid in 56.6% yield.
