Acid‐Catalyzed Redox Isomerizations of 6,8‐Dioxabicyclo[3.2.1]octan‐4‐ols Provide Mechanistic Insights for Levoglucosenone Formation

Author(s)
Lamb, Oscar
Puschnig, Johannes
Glover, Stephen
Greatrex, Ben W
Abstract
<p>Levoglucosenone is an important platform chemical and the principal product of acid-catalyzed cellulose pyrolysis, formed through several intermediates including levoglucosan. An acid-catalyzed redox isomerization of substituted 6,8-dioxabicyclo[3.2.1]octan-4-ols, which could be considered levoglucosan analogues, has been developed using HBr giving (S)-6-hydroxymethyl-dihydro-<i>2H-pyran-3(4H)</i>-ones. Higher yields were obtained when 3,3-disubstitution was present on the ring system, and reactions were faster in acetonitrile. Inclusion of ethylene glycol in the reaction mixture led to the in-situ formation of a ketal adduct, which improved the yield for the parent system. A secondary kinetic isotope effect <i>k<sub>H</sub>/k<sub>D</sub></i> of 1.23for the 3,3-dibenzylated substrate suggested that the mechanism involved elimination rather than hydride transfer, and that ring-opening is the rate-limiting step for the reaction. The facile nature of this transformation further supports a redox-isomer-ization leading to a glucopyran-2-ulose intermediate in the mechanism leading to levoglucosenone from levoglucosan and cellulose, and may have implications for other acid catalyzed reactions of carbohydrates.</p>
Citation
ChemSusChem, p. 1-6
ISSN
1864-564X
Link
Publisher
Wiley-VCH Verlag GmbH and Co KGaA
Title
Acid‐Catalyzed Redox Isomerizations of 6,8‐Dioxabicyclo[3.2.1]octan‐4‐ols Provide Mechanistic Insights for Levoglucosenone Formation
Type of document
Journal Article
Entity Type
Publication

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