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    National Tsing Hua University Institutional Repository > 理學院 > 化學系 > 期刊論文 >  Stereocontrolled synthesis of bicyclic lactone derivatives via tungsten-mediated [3+2] cycloaddition of epoxides with a tethered alkynyl group

    Please use this identifier to cite or link to this item: http://nthur.lib.nthu.edu.tw/dspace/handle/987654321/57807

    Title: Stereocontrolled synthesis of bicyclic lactone derivatives via tungsten-mediated [3+2] cycloaddition of epoxides with a tethered alkynyl group
    Authors: Madhushaw RJ;Li CL;Su HL;Hu CC;Lush SF;Liu RS
    教師: 劉瑞雄
    Date: 2003
    Publisher: American Chemical Society
    Relation: Journal of Organic Chemistry,American Chemical Society,Volume: 68,Issue: 5,Pages: 1872-1877,Published: MAR 7 2003
    Abstract: In the presence of BF3.Et2O, alkynyltungsten complexes underwent [3 + 2] cycloaddition with tethered epoxides to give bicyclic gamma-lactones efficiently. Only one diastereomeric product was formed despite the presence of three stereogenic centers. A mechanism is proposed that involves formation of a tungsten-vinylidenium species via an S(N)2 attack of the epoxide carbon by an alkynyltungsten group to give a tungsten-enol ether species via counterattack at the central tungsten-vinylidenium carbon by the OBF3_ terminus. Most of the tungsten enol ether species were too unstable for isolation and underwent hydrolysis to give only cis-fused gamma-bicyclic lactones. This cyclization works for both cis- and trans-epoxides and tolerates various functional groups. In the case of trans-phenyl epoxide, the reaction led to an addition product via a 6-endo attack of epoxide by the tungsten fragment. This method provides a simple enantiospecific synthesis of complex bicyclic lactones if a chiral epoxide is used in the cyclization. It is also applicable to the one-pot synthesis of bicyclic unsaturated gamma-lactones if a suitable alkynyltungsten functionality is used.
    URI: http://pubs.acs.org/
    Appears in Collections:[化學系] 期刊論文

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