5-Bromo-3,4-dihydroisoquinolin-1(2H)-one (4.3 g, 18.9 mmol) and 2,3-dicyano-5,6-dichloro-1,4-benzoquinone (8.6 g, 37.9 mmol) were mixed in 1,4-dioxane (76 mL). The reaction mixture was stirred at 100 °C for 24 hours. Upon completion of the reaction, the solvent was removed by evaporation and the residue was dissolved in ethyl acetate (500 mL) and washed with 10% aqueous sodium hydroxide solution (2 x 500 mL). The organic and aqueous layers were separated and the aqueous layer was further extracted with ethyl acetate (4 x 300 mL). All organic layers were combined and dried with anhydrous sodium sulfate, then concentrated by evaporation. The product was purified by fast chromatography with the eluent being a solvent mixture of dichloromethane and methanol (ratio tapered from 99:1 to 96:4) to afford 5-bromoisoquinolin-1(2H)-one (1.49 g, 6.65 mmol, 35% yield) as a yellow solid. The product was analyzed by LCMS showing a purity of 94% with a retention time (Rt) of 1.243 min, and electrospray mass spectrometry (ESMS) showed a molecular ion peak m/z of 224 ([M+H]+).
