Rational synthesis of benzimidazole[3]arenes by Cu II -catalyzed post-macrocyclization transformation.

A new series of calix[ n ]arene analogues, benzimidazole[3]arenes, was rationally synthesized by Cu ^II -catalyzed post-macrocyclization transformation of a tris( o -phenylenediamine) macrocycle, and fully characterized by NMR, MS, and single-crystal X-ray diffraction (XRD) analyses. The resulting syn - and anti -benzimidazole[3]arenes have a bowl-shaped and a warped structure, respectively, in their crystalline states, and both display a dynamic inversion behavior in solution. This modification resulted in strong fluorescence due to the generated benzimidazole moieties. The mechanistic study of the post-macrocyclization transformation demonstrated that the formation of both benzimidazole[3]arenes was catalyzed, via triimine intermediates, by Cu ^II ions in air through oxidation and cyclization of the tris( o -phenylenediamine) macrocycle.