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    National Tsing Hua University Institutional Repository > 理學院 > 化學系 > 期刊論文 >  Synthesis of bicyclic pyrane derivatives via tungsten-mediated [3+3] cycloaddition of epoxides with tethered alkynes

    Please use this identifier to cite or link to this item: http://nthur.lib.nthu.edu.tw/dspace/handle/987654321/57788

    Title: Synthesis of bicyclic pyrane derivatives via tungsten-mediated [3+3] cycloaddition of epoxides with tethered alkynes
    Authors: Shen KH;Lush SF;Chen TL;Liu RS
    教師: 劉瑞雄
    Date: 2001
    Publisher: American Chemical Society
    Relation: Journal of Organic Chemistry,American Chemical Society,Volume: 66,Issue: 24,Pages: 8106-8111,Published: NOV 30 2001
    Abstract: Propargyltungsten compounds bearing a tethered epoxide were prepared in short steps from readily available materials. In the presence of various Lewis acids, BF3. Et2O catalysts (25 mol %) most effectively promote the [3 + 3] cycloaddition of the epoxide with its tethered propargyltungsten group, delivering bicyclic pyranyltungsten compounds in reasonable yields. This cyclization proceeds highly diastereoselectively with tolerance of various functional groups. The stereochemical outcome indicates that the cycloaddition is initiated by the ring opening of the epoxides via an exo-attack of the propargyltungsten group. The resulting pyranyltungsten organometallics were demetalated to yield various bicyclic pyranyl derivatives using different oxidants. This new method provides a short enantiospecific synthesis of bicyclic oxygen compounds if chiral epoxide is used in the cyclization. A mechanistic model is presented to rationalize the reaction pathway of this [3 + 3] cycloaddition.
    URI: http://pubs.acs.org/
    Appears in Collections:[化學系] 期刊論文

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