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  • 1
    ISSN: 1434-193X
    Keywords: Intramolecular Diels-Alder reaction ; 1,7,9-Decatrien-3-ones ; α-Eudesmol ; Lewis acids ; Chelates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Trienones 1-3 were subjected to Lewis acid-promoted intramolecular Diels-Alder reactions. It was shown that with monocoordinating Lewis acids the endo selectivity of the cycloaddition was generally high. The preference for either of the two possible endo products cis-a and cis-b, however, was shown to be highly dependent on the nature of the Lewis acid, and on the substitution pattern of the trienone substrates. Lewis acids with two coordination sites furnished predominantly the exo product trans-b via seven-membered ring chelate intermediates. The chelate-controlled intramolecular Diels-Alder reaction was then utilised as the key step in a stereocontrolled synthesis of the sesquiterpene α-eudesmol. This reaction mode, performed on a model trienone, also paved the way for the synthesis of the pharmaceutically important natural product dihydromevinolin.
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1434-193X
    Keywords: Natural products ; Intramolecular Diels-Alder reactions ; 2-Siloxycyclopropanecarboxylates ; 1,7,9-Decatrien-3-ones ; Octalones ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Starting from enones 7 and 8 siloxydienes 9 and 12 were synthesized. Cyclopropanation and subsequent alkylation with sorbyl bromide provided tetrasubstituted siloxycyclopropanes 15 and 16 in good overall efficiency. Their ring cleavage with fluoride reagents gave 1,7,9-decatrienones 5 and 17; the latter was converted into the protected compound 6. The thermal intramolecular Diels-Alder reactions of 5 and 6 were compared with those of related trienones 3 and 4. Octalones 1, 2, 21, and 22 were formed as mixtures of three or four diastereomers. Thus, for the stereoselective construction of natural products such as α-eudesmol or dihydromevinolin alternative reaction conditions for the cycloaddition step have to be developed.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
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