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Reaction of Frustrated Lewis Pairs with Ketones and Esters

Authors

  • Dr. Bao-Hua Xu,

    1. Organisch-Chemisches Institut der Universität Münster, Corrensstrasse 40, 48149 Münster (Germany)
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  • Raul Alfonso Adler Yanez,

    1. Organisch-Chemisches Institut der Universität Münster, Corrensstrasse 40, 48149 Münster (Germany)
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  • Hiroshi Nakatsuka,

    1. Organisch-Chemisches Institut der Universität Münster, Corrensstrasse 40, 48149 Münster (Germany)
    2. Research Center for Materials Science and the Department of Chemistry, Nagoya University, Chikusa, Nagoya 464-8602 (Japan)
    3. On leave to Universität Münster
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  • Prof. Dr. Masato Kitamura,

    1. Research Center for Materials Science and the Department of Chemistry, Nagoya University, Chikusa, Nagoya 464-8602 (Japan)
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  • Dr. Roland Fröhlich,

    1. Organisch-Chemisches Institut der Universität Münster, Corrensstrasse 40, 48149 Münster (Germany)
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    • X-ray crystal structure analyses

  • Dr. Gerald Kehr,

    1. Organisch-Chemisches Institut der Universität Münster, Corrensstrasse 40, 48149 Münster (Germany)
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  • Prof. Dr. Gerhard Erker

    Corresponding author
    1. Organisch-Chemisches Institut der Universität Münster, Corrensstrasse 40, 48149 Münster (Germany)
    • Organisch-Chemisches Institut der Universität Münster, Corrensstrasse 40, 48149 Münster (Germany)

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Abstract

The frustrated Lewis pair (FLP) Mes2PCH2CH2B(C6F5)2 () reacts with an enolizable conjugated ynone by 1,4-addition involving enolate tautomerization to give an eight-membered zwitterionic heterocycle. The conjugated endione PhCO-CH[DOUBLE BOND]CH-COPh reacts with the intermolecular FLP tBu3P/B(C6F5)3 by a simple 1,4-addition to an enone subunit. The same substrate undergoes a more complex reaction with the FLP that involves internal acetal formation to give a heterobicyclic zwitterionic product. FLP reacts with dimethyl maleate by selective overall addition to the C[DOUBLE BOND]C double bond to give a six-membered heterocycle. It adds analogously to the triple bond of an acetylenic ester to give a similarly structured six-membered heterocycle. The intermolecular FLP P(o-tolyl)3/B(C6F5)3 reacts analogously with acetylenic ester by trans-addition to the carbon–carbon triple bond. An excess of the intermolecular FLP tBu3P/B(C6F5)3, which contains a more nucleophilic phosphane, reacts differently with acetylenic ester examples, namely by O[BOND]C(alkyl) bond cleavage to give the {R-CO2[B(C6F5)3]2}[alkyl-PtBu3+] salts. Simple aryl or alkyl esters react analogously by using the borane-stabilized carboxylates as good leaving groups. All essential products were characterized by X-ray diffraction.

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