Breathing Room: Restoring Free Rotation in a Schiff-Base Macrocycle through Endoperoxide Formation.

Macrocyclization is a popular method for preparing hosts, but it can have unintended effects, like limiting molecular free rotation to yield mixtures of inseparable isomers. We report a [3 + 3] Schiff-base macrocycle (1) with anthracene bridges. Restricted rotation about the phenyl-anthracene bonds leads 1 to exist as a mixture of conformations (1Cs and 1C3v). Macrocycle 1 was photooxidized to tris(endoperoxide) adduct 4, alleviating restricted rotation. These results were supported by spectroscopic, structural, and computational analyses.