Superoxide Anion Radical (O2)•-Mediated Base-catalyzed Autoxidation of α-keto Enols

Aryeh A. Frimer, Pessia Gilinsky-sharor, Gladis Aljadeff, Vered Marks, Zilpa Rosental

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Eight 4,4-disubstituted 2-hydroxycyclohexa-2,5-dien-l-ones were prepared by the base-catalyzed autoxidation (BCA) of the corresponding 4,4- or 5,5-disubstituted cyclohex-2-en-l-ones. Upon reaction with superoxide anion radical (02-, generated from K02/18-crown-6) in inert nonpolar aprotic media at room temperature, a-keto enols 3a-g undergo initial deprotonation of the enol hydrogen followed by BCA at C3of the resulting enolate. Aqueous acid workup of the reaction mixture yields lactols 4, while methyl iodide quenching generates methoxy lactones 5. Lactols 4 can be readily converted to their acetoxy analogues 8, opened to aldehydo methyl esters 6, or reduced to the related lactones 7. The latter suggests a convenient one-pot synthesis of 2,3-unsaturated 6-valerolactones from the corresponding cyclohex-2-en-l-ones. 4,4-Diphenyl enol 3h, by contrast, resists BCA (whether mediated by O2-or t-C4H90-) to the corresponding lactol yielding instead a variety of oxidative cleavage products 13–18. 2-Hydroxyspiro[4.5]dec-l-en-3-one (21) also underwent O2 --mediated BCA, yielding diacids 22 and 26 as well as lactol 30. The synthetic applications of these results are also discussed.

Original languageEnglish
Pages (from-to)4866-4872
Number of pages7
JournalJournal of Organic Chemistry
Issue number20
StatePublished - 1 Sep 1989


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