Mechanistic Insights into Ring-Opening and Decarboxylation of 2-Pyrones in Liquid Water and Tetrahydrofuran

Abstract

Abstract2-Pyrones, such as triacetic acid lactone, are a promising class of biorenewable platform chemicals that provide access to an array of chemical products and intermediates. We illustrate through the combination of results from experimental studies and first-principle density functional theory calculations that key structural features dictate the mechanisms underlying ring-opening and decarboxylation of 2-pyrones, including the degree of ring saturation, the presence of C═C bonds at the C4═C5 or C5═C6 positions within the ring, as well as the presence of a β-keto group at the C4 position. Our results demonstrate that 2-pyrones undergo a range of reactions unique to their structure, such as retro-Diels-Alder reactions and nucleophilic addition of water. In addition, the reactivity of 2-pyrones and the final products formed is shown to depend on the solvent used and the acidity of the reaction environment. The mechanistic insights obtained here provide guidance for the selective conversion of 2-pyrones to targeted chemicals. ABSTRACT: 2-Pyrones, such as triacetic acid lactone, are a promising class of biorenewable platform chemicals that provide access to an array of chemical products and intermediates. We illustrate through the combination of results from experimental studies and first-principle density functional theory calculations that key structural features dictate the mechanisms underlying ringopening and decarboxylation of 2-pyrones, including the degree of ring saturation, the presence of CC bonds at the C 4 C 5 or C 5 C 6 positions within the ring, as well as the presence of a β-keto group at the C 4 position. Our results demonstrate that 2-pyrones undergo a range of reactions unique to their structure, such as retro-Diels−Alder reactions and nucleophilic addition of water. In addition, the reactivity of 2-pyrones and the final products formed is shown to depend on the solvent used and the acidity of the reaction environment. The mechanistic insights obtained here provide guidance for the selective conversion of 2-pyrones to targeted chemicals. Disciplines Chemistry | Environmental

Engineering Catalyst Microenvironments for Metal‐Catalyzed Hydrogenation of Biologically Derived Platform Chemicals

“…[10] Using an S. cerevisiae strain engineered for increased precursor availability and an improved 2-PS, we obtained the highest TAL yields described to date, and we have also increased the titer to over 4 g l À1 , the highest reported value. Owing to the fact that TAL undergoes decarboxylation at elevated temperature in water, [11] TAL was then recovered from spent culture media prior to hydrogenation (see the Supporting Information, Section 5). Figure 3 shows that the standard Pd catalyst undergoes rapid deactivation during hydrogenation of recovered and purified TAL, whereas the PVA-overcoated PdAu catalyst is more stable under the same conditions.…”

Engineering Catalyst Microenvironments for Metal‐Catalyzed Hydrogenation of Biologically Derived Platform Chemicals

“…Using an S. cerevisiae strain engineered for increased precursor availability and an improved 2‐PS, we obtained the highest TAL yields described to date, and we have also increased the titer to over 4 g L −1 , the highest reported value. Owing to the fact that TAL undergoes decarboxylation at elevated temperature in water,11 TAL was then recovered from spent culture media prior to hydrogenation (see the Supporting Information, Section 5).…”

Biorenewable chemicals: Feedstocks, technologies and the conflict with food production

“…Sucinnic acid has been a popular platform biorenewable chemical, which has successfully been produced using an integration of biological and chemical techniques. 2-Pyrones such as triacetic acid lactone (TAL) are other such potential platform molecules, which can be obtained from polyketide biosynthetic routes and have been recently shown to produce useful chemicals and fuels via catalytic upgrading [122]. Due to their unique structural features such as the degree of unsaturation, position of the double bond, keto-ester functionality and the nature of substituents on the ring, a variety of catalytic transformations can be performed to obtain a desired product with high yield and selectivity [122].…”