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Polycyclic Aromatic Hydrocarbon with Embedded Azulene Unit
Construction of Polycyclic π-Conjugated Systems Incorporating an Azulene Unit Following the Oxidation of 1,8-Diphenyl-9,10-bis(phenylethynyl)phenanthrene.
Chem. Eur. J. 2018;
20 August 2018 (online)
Incorporation of heptagons and pentagons into a polycyclic aromatic hydrocarbon (PAH) core leads to changes in the molecular geometry and electronic properties of the original PAH. This report demonstrates the use of silver(I) cations to achieve an efficient synthesis of an azulene-embedded PAH 2, which is a challenging issue that is plagued by limited methodologies.
Two-electron oxidation of the silver(I) ion promoted a three-fold transannulation reaction between the aromatic and acetylene units of 1 resulting in the selectively embedded azulenium cation 2H+ , which could be subsequently deprotonated by trimethylamine to afford the neutral azulene-embedded PAH 2. Compound 2 exhibited a low-energy absorption band featuring characteristics of the non-alternant moiety, along with reversible one-electron redox events for the oxidation or reduction of 2, resulting in tropylium cation or cyclopentadienyl anion scaffolds, respectively.