Synthesis, structure, and photoreactions of fluorinated 2,11-diaza[3₂]paracyclophane: Photochemical formation of cage-diene type benzene dimer

An octafluorinated 2,11-diaza[3₂]paracyclophane derivative 12 was prepared, and its photochemical reaction was investigated. Upon irradiation at 300 nm, the fluorinated azacyclophane 12 underwent efficient photodimerization of the benzene cores to afford the corresponding photoisomer 13, which possessed cage diene benzene dimer structure (pentacyclo[6.4.0.0.^2,70.^3,120^6,9]dodeca-4,10-diene skeleton). The cage diene structure was established by single-crystal X-ray diffraction analysis. The cage diene 13 thermally isomerized to a syn-o,o′-dibenzene isomer 22. The activation parameters for the thermal isomerization were determined to be E_a = 121 kJ mol⁻¹, ΔH^≠ = 118 kJ mol⁻¹, ΔS^≠ _(293 K) = 22 J mol⁻¹ K⁻¹, and ΔG^≠ _(293 K) = 111 kJ mol⁻¹. It was revealed that, by photoirradiation at 300 nm, the syn-o,o′-dibenzene isomer 22 underwent facile intramolecular [π4s + π4s] cycloaddition to reproduce the cage diene isomer 13.