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.