Quinoxaline-based U-shaped septuple-bridged [7,7]orthocyclophanes: synthesis, solid-state structure, and self-assembly

We report a three-step synthesis of 12 septuple-bridged [7,7]orthocyclophanes 11 comprising (i) two quinoxaline-based sidewalls and (ii) a linker built-in with a succinimide ring that carries phenyl, p-methoxyphenyl, p-hydroxyphenyl, or p-methoxybenzyl appendants. The synthesis began from the Diels–Alder adduct of 1,2,3,4-tetrachloro-5,5-dimethoxycyclopentadiene (1) and succinimide ring-fused dioxatetracyclodecadiene 9, followed by ruthenium-promoted oxidation of dichloroetheno-bridges in the adduct to generate a bis-α-diketone, which was then condensed with an arene-1,2-diamine to construct sidewalls (phane parts), furnishing U-shaped septuple-bridged [7,7]orthocyclophanes 11 embedding quinoxaline, dimethylquinoxaline, or benzoquinoxaline rings. Concentration-variant 1H NMR spectra of N-p-methoxybenzyl substituted orthocyclophanes (11zd, 11xd, and 11yd) and single-crystal structures of four orthocyclophanes (11xa, 11yd, 11zb, and 11zd) revealed that the U-shaped septuple-bridged [7,7]orthocyclophanes 11 have a tendency of self-assembly, forming V-shaped dimeric entities driven chiefly by intermolecular π–π stacking interaction in both solid state and solution of high concentration.