Synthesis of a deep-cavity thiacalix[4]arene

A novel thiacalix[4]arene derivative bearing four phenyl groups on the upper rim was prepared by the direct condensation of biphenyl-4-ol with elemental sulphur. As revealed by X-ray diffraction analysis, this compound adopts the cone conformation in the solid state, thus creating a cavity with an extended π-aromatic system potentially applicable for solid-state inclusion of suitable molecules. Subsequent alkylation (RI/K2CO3/acetone, R=Me, Et, Pr) yielded tetraalkylated derivatives, which were studied for their conformational preferences using 1H NMR spectroscopy. While the Me or Et derivatives are conformationally mobile and exhibit thermodynamic equilibria of several conformers in solution (CDCl3 or CD2Cl2), the corresponding propoxy derivative is infinitely stable at room temperature.