General procedure for the synthesis of 4-bromo-2,3-dihydro-1H-indene from 4-bromoinden-1-one: Trifluoroacetic acid (TFA) was added to a solution of 4-bromo-2,3-dihydro-1H-inden-1-one (2 g, 10 mmol) in dichloromethane (DCM, 10 mL), and then the reaction mixture was cooled to -20 °C. Triethylsilane (Et3SiH, 15 mL, 1N solution in tetrahydrofuran (THF), 15 mmol) was added dropwise with stirring. The reaction mixture was stirred for 2 h at room temperature and then poured into aqueous ammonium chloride (NH4Cl) and extracted with dichloromethane (DCM, 10 mL x 2). The organic phase was washed with brine (10 mL × 2), dried over anhydrous magnesium sulfate (MgSO4), concentrated and purified by fast chromatography (FC) to afford the target compound 4-bromo-2,3-dihydro-1H-indene (1.7 g, yield: 85%); mass spectra (electrosprayed in positive ion mode, ES+): m/z 197 [M+H]+.
