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A wheel surprise: Reaction of resorcinol and 1,5-pentanedial in ethanol at 80 °C for 48 h in the presence of HCl surprisingly afforded a soluble cyclic oligomer in high yield (83 %) under thermodynamic control. Single-crystal X-ray analysis revealed a waterwheel-like structure with a large hydrophobic hole through the center (see picture). A carboxylic ester derivative of the compound was shown to be highly selective for Rb+ ions.
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Kudo et al. (2006) studied this question.
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