Synthesis, conformations and redox properties of diametrical calix[4]arenediquinones

Several calix[4]arenediquinones3a‐ehaving quinone moieties in opposite positions (diametrical) have been synthesized by oxidation of 25,27‐dialkoxycalix[4]arenes2a‐ewith Tl(NO3)3· 3H2O in organic solvents. The conformational properties of these compounds have been established in the solid state by X‐ray crystallography and in solution by variable‐temperature dynamic NMR. We found that the calix[4]arenediquinones3a‐eare more flexible than the parent 25,27‐dialkoxycalix[4]arenes2a‐ein solution and tend to assume two different partial cone structures in the solid state, depending on the steric bulkiness of the alkoxy groups. Cyclic voltammetry reveals that the redox properties of calix[4]arenediquinones3a‐edepend on their conformational properties.