Under nitrogen protection, tert-butyllithium (1.3 M in pentane, 17.8 mL, 23.2 mmol) was slowly added dropwise to a solution of 3,5-dichloro-1-bromobenzene (5.0 g, 22.1 mmol) in tetrahydrofuran (50 mL) over a period of 30 min, followed by continuing the reaction for 2 h at -78 °C. Upon completion of the reaction, trifluoroacetic anhydride (2.56 g, 12.2 mmol) was slowly added dropwise to the reaction mixture and stirring was continued for 2 hours at -78 °C. The cooling bath was removed and the reaction mixture was allowed to warm slowly to room temperature and stirring was continued at room temperature for 2.5 hours. When the reaction was terminated, saturated ammonium chloride solution (50 mL) was added. The reaction mixture was extracted with ether (3 x 50 mL) and the organic phases were combined and washed with saturated brine (20 mL x 2). The organic phase was separated, dried with anhydrous magnesium sulfate, filtered and concentrated under reduced pressure, and purified by distillation under reduced pressure to give the colorless transparent liquid 3',5'-dichloro-2,2,2-trifluoroacetophenone (2.58 g, 48% yield).
