Reversible Redox Reaction Between Antiaromatic and Aromatic States of 32π-Expanded Isophlorins

摘要

32π-antiaromatic expanded isophlorins with a varying number of thiophene and furan rings adopt either planar, ring-inverted, or twisted conformations depending on the number of furan rings in the macrocycle. However, they exhibit identical reactivity with respect to their oxidation to aromatic 30π-dicationic species under acidic conditions. These 32π-antiawmatic macrocycles can also be oxidized with [Et3O~+SbCl6~-] and NOBF4 to generate dications, thus confirming ring oxidation of macrocycles. Furthermore, they can be reduced back to their parent 32π-antiaromatic state by triethyl-amine, Zn, or FeCl2. Single-crystal X-ray diffraction analysis confirmed a figure-eight conformation for a hexafuran system, which opens to a planar structure upon oxidation.