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

Abstract

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.

The synthesis of oligoether-substituted benzimidazolium bromides and their use as ligand precursors for the Pd-catalyzed Heck coupling in water

“…Substituted-or linled-oligoether functionalized (5,6-dimethyl)benzimidazoles and (5,6-dimethyl)bisbenzimidazoles (1 and 2) were prepared according to a slightly modified procedure from Refs. [5,16]. All reagents were purchased from Merck, Fluka, Alfa Aesar and Acros Organics.…”

Imidazolium receptors for the recognition of anions

“…Temperature dependent conformational studies of o-and m-cyclophane type imidazolium receptors were reported 15,16 while Rajakumar et al 17 published syntheses for benzimidazolophanes and imidazolophanes. However, no anion binding studies were reported.…”

Azolium Cyclophanes

“…While this is also the case in the preparation of many azolium cyclophanes [29] a Isolated yield (%), anion of isolated salt in parentheses. (7)) [19]. (reactant concentrations typically range from less than 1 mM up to 20 mM), some azolium cyclophanes have been prepared at remarkably high concentration in excellent yield.…”

“…This result may be a consequence of the additional methyl groups restricting conformational freedom of the imidazole unit in the intermediate formed during the 3+1 synthesis, and thereby favouring cyclization over polymerization [26]. In some cases solvents have been chosen based on boiling temperature, higher boiling solvents being used to improve reaction rates for less reactive reagents [19]. In these two syntheses of 27 the different solvents used may have been a significant factor in the relative efficiency of the macrocyclization process.…”

“…By providing information about the proximity of various protons in a structure, 1 H NMR NOESY and ROESY experiments have provided insight into conformations of azolium cyclophanes in solution [19]. By providing information about the proximity of various protons in a structure, 1 H NMR NOESY and ROESY experiments have provided insight into conformations of azolium cyclophanes in solution [19].…”