Triptycene-derived oxacalixarenes as new wheels for the synthesis of [2]rotaxanes: acid-base- and metal-ion-switchable complexation processes

A pair of triptycene-derived oxacalixarenes, 1a and 1b, containing two naphthyridine subunits have been synthesized by a convenient one-pot approach. Macrocycles 1a and 1b are diastereomers, with 1a being a cis isomer with a boat-like 1,3-alternate conformation and 1b being a trans isomer with a curved boat-like conformation in the solid state. Both 1a and 1b have fixed conformations in solution at room temperature, as revealed by variable-temperature (1)H NMR spectroscopy experiments. It was found that oxacalixarenes 1a and 1b could both form 1:1 2]pseudorotaxane-type complexes with paraquat derivatives with different functional groups in solution and in the solid state, which resulted in the further synthesis of a pair of novel isomeric 2]rotaxanes. Moreover, the controlled dethreading and rethreading processes of the 2]pseudorotaxanes were also easily achieved by acid-base stimuli or Hg(2+) association/dissociation.