Synthesis and Isolation of Antiaromatic Expanded Azacoronene via Intramolecular Vilsmeier-Type Reaction

摘要

An antiaromatic cation of the expanded hexapyrrolohexaazacoronene (HPHAC) 1(+) was synthesized by a Vilsmeier-type reaction of the partially unfused HPHAC 2. X-ray diffraction analysis revealed the formation of a seven-membered ring with a methyne linkage between the pyrrole moieties. Although 1(+) is a monocation, upfield shifts of the peripheral ethyl protons were clearly observed in the H-1 NMR spectra, indicating 24 pi antiaromaticity. Global antiaromaticity was also supported by nucleus-independent chemical shift and anisotropy of the induced current density calculations. Cation 1(+) displayed two reversible oxidations and one irreversible reduction in the cyclic voltammetry measurements. Treatment of 1(+) with NOSbF6 gave aromatic trication 1(3+) with 22 pi-electron conjugation.