Step 2: Dissolve 4-methyl-2H-isoquinolin-1-one (4.8 g) in phosphorous trichloride (50 mL) and heat to reflux for 3 hours. Upon completion of the reaction, it was cooled to room temperature and concentrated under reduced pressure. The residue was treated with 5 N aqueous sodium hydroxide and subsequently extracted with dichloromethane. The organic layers were combined, washed with saturated brine and dried over anhydrous magnesium sulfate. After filtration, the filtrate was concentrated under reduced pressure and the resulting crude product was purified by Biotage fast chromatography, the eluent being a hexane solution of 5% ethyl acetate to give 4.8 g (90% yield) of the target product, 1-chloro-4-methylisoquinoline, as a white solid. The structure of the product was confirmed by 1H NMR (400 MHz, CDCl3): δ 2.59 (s, 3H), 7.68 (t, J = 7.70 Hz, 1H), 7.78 (m, 1H), 7.94 (d, J = 8.31 Hz, 1H), 8.11 (s, 1H), 8.35 (d, J = 8.31 Hz, 1H).
