Planar Antiaromatic Core‐Modified 24π Hexaphyrin(1.0.1.0.1.0) and 32π Octaphyrin(1.0.1.0.1.0.1.0) Bearing Alternate Hybrid Diheterole Units.

The Lewis acid catalyzed self‐condensation of hybrid diheterole (furan‐pyrrole and thiophene‐pyrrole) precursors has afforded novel Hückel antiaromatic 24π hexaphyrin(1.0.1.0.1.0) and 32π octaphyrin(1.0.1.0.1.0.1.0) structures without β‐annulated bridges. Single‐crystal X‐ray diffraction analysis of the hybrid porphyrinoids (S3N3‐ox and O4N4‐ox) revealed a nearly planar conformation and the 1H NMR spectra suggest the presence of paratropic ring currents. These antiaromatic macrocycles show characteristic optical features and underwent reversible two‐electron reduction to Hückel aromatic 26π‐ and 34π‐electron species, respectively, as is evident from the results of spectroscopic and theoretical studies (nucleus‐independent chemical shift (NICS) and anisotropy of the current‐induced density (ACID) calculations). The incorporation of hybrid diheteroles alternately into expanded porphyrin skeletons provides a novel approach to the fine‐tuning of the electronic structures of planar antiaromatic macrocycles. Antiaromatic macrocycles: The Lewis acid catalyzed self‐condensation of hybrid diheterole precursors has afforded Hückel antiaromatic 24π hexaphyrin and 32π octaphyrin structures that have been structurally characterized. The incorporation of hybrid diheteroles alternately into the expanded porphyrin skeletons could provide a novel approach to the fine‐tuning of the electronic structures of planar antiaromatic macrocycles. [ABSTRACT FROM AUTHOR]