Different Reaction Modes for the Oxidative Dimerization of Epoxyquinols and Epoxyquinones. Importance of Intermolecular Hydrogen-Bonding

Mitsuru Shoji, Hiroki Imai, Isamu Shiina, Hideaki Kakeya, Hiroyuki Osada, Yujiro Hayashi

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Abstract

An oxidative dimerization reaction, involving the three successive steps of oxidation, 6π-electrocyclization, and Diels-Alder reaction, has been experimentally and theoretically investigated for the three 2-alkenyl-3-hydroxymethyl-2-cyclohexen-1-one derivatives epoxyquinol 3, epoxyquinone 6, and cyclohexenone 10. Of the sixteen possible modes of the oxidation/6π-electrocylization/Diels-Alder reaction cascade for the epoxyquinone 6, and eight for the cyclohexenone 10, only the endo-anti(epoxide)-anti(Me)-hetero and endo-anti(Me)-hetero modes are, respectively, observed, while both endo-anti(epoxide)-anti(Me)-hetero and exo-anti(epoxide)-anti(Me)-homo reaction modes occur with the epoxyquinol 3. Intermolecular hydrogen-bonding is found to be the key cause of formation of both epoxyquinols A and B with 3, although epoxyquinone 6 and cyclohexenone 10 both gave selectively only the epoxyquinol A-type product. In the dimerization of epoxyquinol 3, two monomer 2H-pyrans 5 interact with each other to afford intermediate complex 28 or 29 stabilized by hydrogen-bonding, from which Diels-Alder reaction proceeds. Theoretical calculations have also revealed the differences in the reaction profiles of epoxyquinone 6 and cyclohexenone 10. Namely, the rate-determining step of the former is the Diels-Alder reaction, while that of the latter is the 6π-electrocyclization.

Original languageEnglish
Pages (from-to)1548-1556
Number of pages9
JournalJournal of Organic Chemistry
Volume69
Issue number5
DOIs
Publication statusPublished - 2004 Mar 5

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ASJC Scopus subject areas

  • Organic Chemistry

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