Synthesis and Isolation of Antiaromatic Expanded Azacoronene via Intramolecular Vilsmeier-Type Reaction
Kosuke Oki1, Masayoshi Takase1, Shigeki Mori2
1Graduate School of Science and Engineering , Ehime University , Matsuyama 790-8577 , Japan.
Abstract:
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 1H NMR spectra, indicating 24π 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 with 22π-electron conjugation.
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