Gleeson, Duangkamol

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Gleeson, Duangkamol
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Email
duangkamol.gl@kmitl.ac.th

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    Item type:Publication,
    Computational investigation of the radical-mediated mechanism of formation of difluoro methyl oxindoles: Elucidation of the reaction selectivity and yields
    (2023-02-15)
    Somnarin, Thanachon
    ;
    Krawmanee, Pacharaporn
    ;
    Gleeson, Matthew Paul
    ;
    Gleeson, Duangkamol
    Oxindoles are an important class of heterocyclic alkaloids with demonstrated pharmacological activity at multiple biological targets. Preparation of new analogs through novel synthetic routes is therefore highly attractive. In this work, we report a computational study to investigate the synthesis of ethoxycarbonyldifluoromethylated oxindoles from N-arylmethacrylamides. The reaction tolerates a diverse range of acrylamides, shows yields ranging from approximately 38%–96%. We have applied density functional theory (DFT) to explore the reaction mechanism, kinetics and thermodynamics to gain further understanding. We demonstrate that a radical-based ring closure reaction is energetically more favorable than a heterolytic process, that the rate-determining step is the formation of the arylmethacrylamide radical, and that the product yields and selectivities are consistent with experiment. The results demonstrate that theoretical methods can prove useful to understand how such reaction and could be potentially employed to rapidly explore the reaction scope further.
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    Item type:Publication,
    Computational Investigation of the Ru-Mediated Preparation of Benzothiazoles From N-Arylthioureas: Elucidation of the Reaction Mechanism and the Origin of Differing Substrate Reactivity
    (2024-10-01)
    Krawmanee, Pacharaporn
    ;
    Gleeson, M. Paul
    ;
    Gleeson, Duangkamol
    Synthesis of novel benzothiazoles via intramolecular CS bond formation reactions is increasingly being explored since they have been found in a wide range of natural products and pharmaceutical agents. Sharma et al. reported the ruthenium-catalyzed preparation of novel benzothiazole derivatives from N-arylthiourea precursors, with a range of reaction yields and selectivity being observed. We have employed a density functional theory-based computational model to investigate the reaction mechanism leading to the benzothiazole product and help uncover the origin of the differing experimental yields and substrate specificities. We proposed a modified mechanistic scheme where the rate-determining step to be the synchronized breaking of the peroxide bond of the oxidizing agent with the concomitant proton-coupled electron transfer from the haloarene urea and a Ru-bound water molecule, not electrophilic RuC bond activation. Evidence for this being the rate-determining step is (a) the barrier is consistent with a lack of kinetic isotope effects associated with the ortho-H atom and (b) the computed rate-determining barriers for 10 N-arylthiourea substrates show good correlation with the observed yield.