Highly soluble bisurea derivatives for anion recognition

Highly soluble bisurea derivatives having 1,2-phenoxyethane (receptors 2) and 1,2-ethoxyethane (3) moieties as spacer groups were designed and prepared based on previously reported receptors with the 2,2'-binaphthyl group as a spacer (1). The receptors can be prepared in fewer steps from commercially available starting materials. The solubilities and anion recognition abilities were evaluated by UV-vis and NMR spectral methods. Receptors 2 and 3 bearing a flexible linker showed good solubilities in common organic solvents such as CHCl₃, MeCN, 2-butanone, toluene, and THF. Although the anion recognition abilities of receptors 2 and 3 were lower than those of receptors 1, the greatly improved solubilities of receptors 2 and 3 allow the association of anions under more concentrated conditions for the solubilisation of salts such as lithium chloride in organic solvents.