Synthesis and Conformational Analysis of Dicationic N,N′-Bridged Bis(benzimidazolium) and Bis(imidazolium) Macrocycles

Two-step alkylations of benzimidazole, 2-methylbenzimidazole, and imidazole at their nitrogen atoms with various bifunctional alkylating agents have afforded a series of 16-membered quaternary azacyclophanes. Of these macrocycles, those bearing methyl or methoxy groups on the azole or at the aromatic bridges have been found to exist as mixtures of conformers. In some cases, the structures of the conformers have been determined by NMR methods and X-ray crystallography, and have been correlated with the results of a computer-aided conformational search.