Intramolecular Domino Electrophilic and Thermal Cyclization of peri-Ethynylene Naphthalene Oligomers

Authors

  • Dr. Xiaobo Huang,

    1. Department of Chemistry, National University of Singapore, 3 Science Drive 3, 117543 (Singapore), Fax: (+65) 6779-1691
    2. College of Chemistry and Materials Engineering, Wenzhou University, Wenzhou, 325035 (P. R. China)
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  • Dr. Lintao Zeng,

    1. Department of Chemistry, National University of Singapore, 3 Science Drive 3, 117543 (Singapore), Fax: (+65) 6779-1691
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  • Zebing Zeng,

    1. Department of Chemistry, National University of Singapore, 3 Science Drive 3, 117543 (Singapore), Fax: (+65) 6779-1691
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  • Prof. Jishan Wu

    Corresponding author
    1. Department of Chemistry, National University of Singapore, 3 Science Drive 3, 117543 (Singapore), Fax: (+65) 6779-1691
    • Department of Chemistry, National University of Singapore, 3 Science Drive 3, 117543 (Singapore), Fax: (+65) 6779-1691
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Abstract

The intramolecular electrophilic or thermal cyclization of arylene ethynylene precursors recently became a powerful method for the synthesis of new polycyclic aromatic hydrocarbons (PAHs). In this work, we investigated in detail the synthesis and intramolecular cyclization reaction of a series of peri-ethynylene naphthalene oligomers in which the ethynylene units are fixed in close proximity within the naphthalene framework. The high reactivity of these precursors led to simultaneous thermal cyclization reactions, even during their syntheses. Electrophilic cyclizations with iodine were also undertaken. Several new PAHs containing five-membered rings, for example, indeno[2,1-a]phenalene, acenaphtho[1,2-a]pyrene, and benzo- or naphtho-annulated fluoranthene derivatives, were synthesized and their structures were unambiguously determined by X-ray crystallographic analysis. Plausible mechanisms were proposed and it was demonstrated that oligomers most probably underwent intramolecular domino cyclization via either radical or cationic intermediates. The photophysical and electrochemical properties of these new PAHs were investigated and some of them displayed amphoteric redox behavior, due to the existence of five-membered rings.

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