A Modular and Scalable Synthesis of Imidazole‐Embedded Crown Ethers and Evaluation of Their Cation Binding Properties

A modular and scalable synthetic route to imidazole‐containing crown ethers has been developed, enabling access to a homologous series of macrocycles ranging from 15‐ to 24‐membered rings. Central to the strategy is the concise synthesis of 2,4‐bis(hydroxymethyl)imidazole, obtained selectively in three steps and with a 36% overall yield without the need for protecting‐group manipulations. The cation‐binding properties of the imidazole‐containing crown ethers toward sodium and potassium hexafluorophosphate salts were studied, showing binding affinities comparable to those of classical crown ethers, while exhibiting donor properties intermediate between ether‐ and pyridine‐containing analogs. The enhanced basicity and hydrogen‐bond acceptor ability of the imidazole unit had a more pronounced effect on secondary ammonium recognition. In particular, a highly stable pseudorotaxane with dibenzylammonium hexafluorophosphate could be formed with an association constant of approximately 1 × 10 4 M −1 in acetonitrile. This value ranks among the highest reported for crown ether‐based pseudorotaxane systems under comparable conditions.