The general procedure for the synthesis of 5-bromo-3,4-dihydroquinolin-2(1H)-one from 4-bromoinden-1-one was as follows: a three-phase mixture consisting of sodium azide (18.5 g, 284 mmol), concentrated sulfuric acid (18.8 M, 4.8 mL, 90 mmol), water (36 mL), and chloroform (144 mL) was stirred for 2.5 hours at 0 °C. Upon completion of the reaction, the phases were separated and the organic phase was dried over anhydrous sodium sulfate and filtered. The filtrate was slowly added to a solution of 4-bromoindan-1-one (12.0 g, 56.9 mmol) in chloroform (215 mL). Subsequently, concentrated sulfuric acid (18.8 M, 18.7 mL, 351.6 mmol) was added dropwise over 10 minutes. The reaction mixture was stirred at 45°C for 4 hours, then cooled to room temperature and continued stirring for 20 hours. At the end of the reaction, the mixture was poured into ice (200 g) and neutralized by adding 10% aqueous sodium hydroxide solution (50 mL). The phases were separated and the aqueous phase was extracted with chloroform (100 mL). All organic phases were combined and the solvent was evaporated by drying with anhydrous sodium sulfate. The crude product was purified by recrystallization from ethanol (55 mL) to afford 5-bromo-3,4-dihydroquinolin-2(1H)-one (8.65 g, 38.2 mmol, 67% yield) as an off-white powder. The product was analyzed by LCMS showing a purity of 98% with a retention time (Rt) of 1.290 min and m/z 226 ([M+H]+) detected by ESMS.
