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Issue 7, 2005
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On the Diels–Alder reactions of pentadienyl maleates and citraconates

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Reactions between conjugated dienols and maleic anhydride provide eithercis-fused or trans-fused bicyclic products as major products, depending upon how the reaction is carried out. Simply mixing the two reactants together generally leads to cis-fused lactone acids in thermal reactions which proceed viaintermolecular Diels–Alder reaction followed by intramolecular esterification. Pre-forming the maleate half ester derivative followed by heating affords predominantly trans-fused lactone acids in good yields by way of an intramolecular Diels–Alder (IMDA) reaction. Sorbyl citraconate half esters undergo a rapid thermolytic fragmentation in refluxing toluene to form the dienol and citraconic anhydride. The resulting diene–dienophile pair undergo an intermolecular cycloaddition followed by a rapid intramolecular esterification to give cis-fused bicyclic lactone acids as major products. The IMDA reaction of citraconic half esters is sufficiently rapid in DMSO to dominate over fragmentation: the exo-cycloadduct is formed almost exclusively. Nine literature reports of endo-selective IMDA reactions of triene acids are erroneous; the cycloadditions proceed in an intermolecular manner.

Graphical abstract: On the Diels–Alder reactions of pentadienyl maleates and citraconates

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The article was received on 28 Jan 2005, accepted on 16 Feb 2005 and first published on 04 Mar 2005

Article type: Paper
DOI: 10.1039/B501446H
Citation: Org. Biomol. Chem., 2005,3, 1302-1307

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    On the Diels–Alder reactions of pentadienyl maleates and citraconates

    T. N. Cayzer, M. J. Lilly, R. M. Williamson, M. N. Paddon-Row and M. S. Sherburn, Org. Biomol. Chem., 2005, 3, 1302
    DOI: 10.1039/B501446H

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