[2.2]Paracyclophane (4.0 g, 19.2 mmol, 1.00 equiv.) was dissolved in dichloromethane (380 mL) and cooled to 0 °C. A mixture of sulfuric acid (95% aq. solution, 4.31 mL, 76.8 mmol, 4.00 equiv.) and nitric acid (70% aq. solution, 2.29 mL, 38.4 mmol, 2.00 equiv.) was slowly added. The mixture was warmed to room temperature. After 16 h, the reaction mixture was decanted onto the ice, leaving any dark orange tar in the reaction vessel. The biphasic mixture was stirred for 15 min, and the layers were separated. The aqueous phase was extracted with dichloromethane (3 × 100 mL). The combined organic layers were dried over sodium sulfate, and the solvent was removed under reduced pressure. The crude solid was purified by flash column chromatography on silica gel using dichloromethane /cyclophane 1:1) to yield the title compound (5.20 g, 20.5 mmol, 43%) as a yellow solid.
