A stirred solution of tert-butyl 4-(4-hydroxy-2-oxo-1,2,3,4-tetrahydro-quinolin-3-yl)-piperidine-1-carboxylate (5.60 g, 16.2 mmol) in ethyl acetate (70 mL) was treated with HCl/dioxane (4N, 40 mmol, 10 mL). The mixture was stirred at room temperature for 45 minutes. Then HCl/dioxane (4N, 120 mmol, 30 mL) was added and stirring was continued for 16 hours at room temperature. The resulting solid was collected by filtration and washed with ethyl acetate. It was then suspended in 5% water-isopropanol (100 mL) and the mixture was warmed to reflux and stirred for 20 minutes. The mixture was cooled to room temperature and stirred at room temperature for 16 hours. The solid was collected by filtration, washed with isopropanol and dried under high vacuum. 3-(Piperidin-4-yl)-1,2-dihydroquinolin-2-one hydrochloride was obtained in 75% yield as a white solid.
