Synthesis of Methylene-Bridge Polyarenes through Palladium-Catalyzed Activation of Benzylic Carbon-Hydrogen Bond

Authors

  • Chien-Chi Hsiao,

    1. Department of Chemistry, National Cheng Kung University. No. 1 Ta-Hsueh Rd., 70101 Tainan, Taiwan, Republic of China, Fax: (+886)-6-274-0552
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  • Yi-Kuan Lin,

    1. Department of Chemistry, National Cheng Kung University. No. 1 Ta-Hsueh Rd., 70101 Tainan, Taiwan, Republic of China, Fax: (+886)-6-274-0552
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  • Chia-Ju Liu,

    1. Department of Chemistry, National Cheng Kung University. No. 1 Ta-Hsueh Rd., 70101 Tainan, Taiwan, Republic of China, Fax: (+886)-6-274-0552
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  • Tsun-Cheng Wu,

    1. Department of Chemistry, National Cheng Kung University. No. 1 Ta-Hsueh Rd., 70101 Tainan, Taiwan, Republic of China, Fax: (+886)-6-274-0552
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  • Yao-Ting Wu

    Corresponding author
    1. Department of Chemistry, National Cheng Kung University. No. 1 Ta-Hsueh Rd., 70101 Tainan, Taiwan, Republic of China, Fax: (+886)-6-274-0552
    • Department of Chemistry, National Cheng Kung University. No. 1 Ta-Hsueh Rd., 70101 Tainan, Taiwan, Republic of China, Fax: (+886)-6-274-0552
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Abstract

In the presence of palladium(II) acetate [Pd(OAc)2] and an N-heterocyclic carbene (NHC) ligand, fluorene derivatives can be generated in good to excellent yields from 2-halo-2′-methylbiaryls through the benzylic C[BOND]H bond activation (14 examples; 81–97% yields). The scope and limitations of this protocol have been examined. A wide range of functional groups, such as alkyl, alkoxy, ester, nitrile, and others, is able to tolerate the reaction conditions herein. The cyclization of an isotope-labelled biphenyl gave the corresponding product with a primary kinetic isotope effect (kH/kD=4.8:1), which indicates that the rate-determining step of this reaction is the activation of the benzylic C[BOND]H bond. Moreover, indenofluorenes were also accessed in excellent results from terphenyls (3 examples; 91–92% yields). The cascade reaction of 2,6-dichloro-2′-methylbiphenyl with diphenylacetylene produced 8,9-diphenyl-4H-cyclopenta[def]phenanthrene in 60% yield through the activation of an aryl and a benzylic C[BOND]H bond.

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