On the Diels–Alder reactions of pentadienyl maleates and citraconates
| Autor: | Rachel M. Williamson, Michael J. Lilly, Tory N. Cayzer, Michael N. Paddon-Row, Michael S. Sherburn |
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| Rok vydání: | 2005 |
| Předmět: | |
| Zdroj: | Org. Biomol. Chem.. 3:1302-1307 |
| ISSN: | 1477-0539 1477-0520 |
| DOI: | 10.1039/b501446h |
| Popis: | Reactions between conjugated dienols and maleic anhydride provide either cis-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. |
| Databáze: | OpenAIRE |
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