At 0 °C, 6-nitro-3,4-dihydroquinolin-2(1H)-one (3 g) was dissolved in methanol (60 mL) and zinc powder (5 eq.) and ammonium chloride (5 eq.) were added sequentially. The reaction mixture was stirred at room temperature for 1 h. The reaction progress was monitored by thin layer chromatography (TLC). Upon completion of the reaction, the mixture was filtered through a bed of diatomaceous earth and the filtrate was concentrated under reduced pressure. The residue was dissolved in a dichloromethane solution containing 5% methanol and subsequently washed with water. The organic layer was dried with anhydrous sodium sulfate, filtered and concentrated under reduced pressure to afford 6-amino-3,4-dihydroquinolin-2(1H)-one (2.3 g in 91% yield. The product was characterized by 1H NMR (DMSO-d6, 400MHz): δ 9.654 (broad single peak, 1H), 6.53 (double peak, 1H), 6.378-6.334 (multiple peaks, 2H), 4.707 (broad single peak, 2H), 2.699 (triple peak, 2H), 2.330 (triple peak, 2H).
