Synthesis of A Molecular Waterwheel

Significance

A unique double-cyclic ladder-type oligomer (4) with a central hole, which resembles a waterwheel architecture, was synthesized in one step via the condensation reaction of resorcinol (1, difunctional unit) with 1,5-pentanedial (2, tetra­functional unit). Compound 4 was characterized by NMR spectroscopy, mass spectrometry as well as X-ray single crystal analysis. Mechanism studies by examining the size-exclusion chromatography (SEC) profiles of the obtained products over time revealed that compound 3 is the key intermediate on the reaction pathway leading to the final product formation. The ester derivative of 4 showed excellent selectivity for Rb⁺ ion, which was presumably enclosed in the central hole in the molecule.