Bromine (3.92 g, 1.26 mL, 25.0 mmol, 1.00 equiv.) was diluted with dichloromethane (40 mL). From this solution, 5.0 mL were added to iron powder (27.0 mg, 483 μmol, 2.0 mol%) and stirred at room temperature for 1 h. The reaction mixture was diluted with dichloromethane (80 mL) and [2.2]paracyclophane (5.00 g, 24.0 mmol, 1.00 equiv.) was added portion-wise and stirred for further 30 min. The remaining bromine solution was slowly added over a period of 5 h and the mixture was stirred overnight. Sodium sulfite (sat. aq. solution, 150 mL) was added and stirred until the organic phase was colorless. The phases were separated, and the aqueous layer was extracted with dichloromethane (3 x 100 mL). The combined organic phases were dried over sodium sulfate and the solvent was removed under reduced pressure to obtain the title compound (6.80 g, 24 mmol, 99%) as an off-white solid.
