Vasarene and vasarene-analogues: Synthesis and characterization of self-assembled, voluminous ligands with specific affinity to M⁺F^- ion-pairs

Vasarene is a vase-shaped compound readily obtained by the reaction between ninhydrin and phloroglucinol (1,3,5-benzenetriol). Vasarene has shown a special affinity towards alkali fluoride ion-pairs, forming with them cage-like supramolecular structures composed of several vasarene units encapsulating the alkali fluoride salt. Here we report the preparation and characterization of a series of geometrically modified vasarenes containing only two 'side-walls' instead of three, and their derivatives. Synthesis under microwave conditions could be accomplished within minutes compared to hours for 'regular' solvent heating. Like vasarene, the new analogues have also demonstrated a selective affinity to alkali- and tetraalkyl ammonium-fluorides including inter alia their solubilization in organic solvents and precipitation from aqueous solutions.