Threading of Conformationally Stable Calix[6]arene Wheels Substituted at the Methylene Bridges

Calix­[6]­arenes disubstituted at the methylene bridges, which are stable in the cone or 1,2,3-alternate conformation, form pseudorotaxanes with dialkylammonium axles. The cone wheel-based pseudorotaxanes are 10–100 times more stable than those obtained with the native conformationally mobile calix[6]­arene wheel, as a consequence of their higher degree of preorganization. The threading of conformationally stable 1,2,3-alternate calix[6]­arenes is unprecedented in the literature. Therefore, very peculiar NMR features are here evidenced for this threading process involving the less symmetrical 1,2,3-alternate calix[6]­arene conformation, which implies a peculiar rototranslation motion of the axle.