Chiral benzimidazole-derived mono azacrowns: synthesis and enantiomer recognition studies with chiral amines and their ammonium salts

Benzimidazole fused chiral mono aza-15-crown-5 2, was obtained in a single step from (S)-(−)-2-(α-hydroxyethyl) benzimidazole 1. This new class of aza-crown has a unique structure with the chiral unit being held in a stable conformation due to adjacent benzimidazole ring contributing to its stereodiscrimination ability. The interactions between the host aza-crown and enantiomerically pure amine guests in ionic and neutral forms exhibited the enantio-discrimination ability. The preliminary evaluation of the chiral sensing was monitored using 1H NMR and circular dichroism (CD) analysis of the complexes at their molar equivalence. The binding parameters were determined using electronic absorption spectroscopy.