6-Bromo-1,1-dimethyl-2,3-dihydro-1H-indene (3.6 g, 16 mmol) was used as a raw material and dissolved in acetic acid (50 mL). Subsequently, an oxidizer solution prepared from CrO3 (9.6 g, 96.0 mmol) dissolved in 50% aqueous acetic acid (50 mL) was added to this solution. The reaction mixture was heated and stirred at 60 °C for 3 hours. Upon completion of the reaction, the reaction was quenched by addition of isopropanol (20 mL). The quenched reaction mixture was partitioned between EtOAc (200 mL) and 0.25 M NaOH aqueous solution (100 mL). The organic layer was separated and the aqueous phase was further extracted with EtOAc (2 × 100 mL). All organic phases were combined, washed with brine, dried over anhydrous Na2SO4, filtered and concentrated. Purification by rapid chromatography on silica gel (with 50% EtOAc/hexane as eluent) afforded the target product 5-bromo-3,3-dimethyl-2,3-dihydro-1H-inden-1-one (2.91 g, 76% yield) as a white solid. The product was confirmed by 1H NMR (400 MHz, chloroform-d): δ 7.65 (s, 1H), 7.47-7.58 (m, 2H), 2.58 (s, 2H), 1.42 (s, 6H); mass spectrum (EI) m/z = 240.1 [M + 1]+.
