A solution of sodium hydrosulfite (43.35 g, 249 mmol) and potassium carbonate (38.28 g, 277 mmol) in water (300 mL) was added to a mixture of tert-butyl[4-(7-bromo-3-nitroquinolin-4-ylamino)butyl]carbamate (24.3 g, 55.3 mmol) and 1,1′-diethyl-4,4′-bipyridinium dibromide (1.03 g, 2.76 mmol) in dichloromethane (368 mL) and water (40 mL), and the reaction was stirred overnight at ambient temperature. The reaction mixture was filtered through a layer of CELITE filter aid. The aqueous filtrate was extracted with dichloromethane, and the combined organic fractions were dried over magnesium sulfate, filtered, and concentrated under reduced pressure to provide 22.4 g of tert-butyl[4-(3-amino-7-bromoquinolin-4-ylamino)butyl]carbamate as a brown powder.
