Inverted azolophanes: alternant o-heteroarene/p-arene macrocycles

Using the Debus-Radziszewski reaction, eight imidazole-based macrocycles were synthesized from cyclotetrabenzil, while three oxazole analogs were prepared by the Davidson oxazole synthesis starting with cyclotetrabenzoin esters. These macrocycles were dubbed "inverted azolophanes" as their azole valences point divergently outside of the central ring, in contrast to the more studied azolophane architectures. Crystal structures of five macrocycles were obtained and show largely coplanar fusion of the 24-membered central macrocycle and the four azole rings. Despite the formal possibility of a 24-membered antiaromatic ring current, inverted azolophanes show ring currents firmly localized in their six- and five-membered rings. The roughly square-shaped connectivity of the available azole valences and the shape-persistent nature of the macrocycles bode well for their use as tetragonal building blocks for the construction of ordered frameworks.