General procedure for the synthesis of 4-bromo-7-fluoroindanone using 7-fluoro-2,3-dihydro-1H-inden-1-one as starting material: 7-fluoro-2,3-dihydro-1H-inden-1-one (5.3 g, 35.3 mmol) was added to a solution of aluminum chloride (11.77 g, 88 mmol) in dichloroethane (100 mL) at room temperature, followed by a slow, dropwise addition of bromine ( 1.91 mL, 37.1 mmol). The reaction mixture was heated at 65 °C with stirring for 16 hours. Upon completion of the reaction, the mixture was cooled to room temperature and carefully poured into a mixture of ice and 1N aqueous hydrochloric acid solution. The mixture was extracted with ether (200 mL x 2) and the organic phases were combined. The organic phase was dried with anhydrous magnesium sulfate, filtered and concentrated under reduced pressure. The crude product was purified by silica gel column chromatography with an eluent gradient of 0-10% ethyl acetate/hexane to give 4-bromo-7-fluoroindanone (5.2 g, 64% yield). The mass spectrum (DC1/NH3) showed m/z 246 (M + NH4)+.
