Acetyl chloride → 2-Acetyl-3-bromo-benzothiophene

To a mixture of 3-bromothianaphthene (Sigma-Aldrich Chemical Company, 2.000 mL, 9.39 mmol) and aluminum chloride (1.002 mL, 9.39 mmol) in DCM (50 mL) cooled with an ice bath was added acetyl chloride (0.667 mL, 9.39 mmol) via syringe, in one minute. The resulting intense orange reaction solution was stirred at rt for 1 h. The reaction was poured into ice and partitioned between water and DCM. The aqueous layer was extracted with DCM, and the combined extracts were washed with 50 mL 5% aqueous sodium hydroxide, 50 mL brine, and stirred over anhydrous magnesium sulfate, filtered and concentrated under reduced pressure to give 1-(3-bromobenzo[b]thiophen-2-yl)ethanone as a pale yellow solid. 1H NMR (400 MHz, DMSO-d6) δ 2.77 (s, 3H), 7.57-7.65 (m, 2H), 7.95 (dd, J=7.7, 1.1 Hz, 1H), 8.10 (dd, J=7.1, 1.3 Hz, 1H); LC-MS (ESI)] m/z 254.9 [M+H]+.