3,4-Dihydroquinolin-2(1H)-one (2.73 g, 18.55 mmol) was dissolved in N,N-dimethylacetamide (30 mL) and N,N-dimethylacetamide (10 mL) solution of N-bromosuccinimide (3.30 g, 18.55 mmol) was added slowly and dropwise in an ice water bath. The reaction solution continued to react in an ice water bath with stirring for 6 hours and then warmed up to room temperature for 12 hours. At the end of the reaction, water (50 mL) was added to the reaction mixture and extracted with ethyl acetate (50 mL x 3). The organic phases were combined, dried with anhydrous sodium sulfate, filtered, and concentrated under reduced pressure, and the resulting residue was purified by silica gel column chromatography (petroleum ether/ethyl acetate (v/v) = 3/1) to afford the title compound as a white solid (3.86 g, 92.1%).
