To a suspension of 5-acetyl-8-(benzyloxy)quinolin-2(1H)-one (19.4 g, 66.4 mmol) in anhydrous THF (240 mL) and anhydrous methanol (165 mL) was added a solution of tetra-n-butylammonium tribromide (54.5 g, 113.0 mmol) in anhydrous THF (130 mL) dropwise over 1.5 hours. The resulting solution was stirred at RT overnight before concentrating under reduced pressure without heating. The residue was re-dissolved in methanol (200 mL). Saturated aqueous ammonium chloride solution (390 mL) was added with ice-cooling. The resulting suspension was filtered, and the solid washed with water and air-dried under vacuum. The solid was suspended in DCM and methanol (1:1 v/v, 100 mL) for 90 minutes. The solid was collected by filtration, washed with DCM and air-dried to afford the title compound (18.0 g, 73%).
