Stepwise Mechanisms in the Ene Reaction of Alpha,Beta-Unsaturated Esters with N-Phenyl-1,2,4-Triazoline-3,5-Dione and Singlet Oxygen - Intermolecular Primary and Secondary Hydrogen Isotope Effects
Stepwise Mechanisms in the Ene Reaction of Alpha,Beta-Unsaturated Esters with N-Phenyl-1,2,4-Triazoline-3,5-Dione and Singlet Oxygen - Intermolecular Primary and Secondary Hydrogen Isotope Effects
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Elemes, Y.
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Πανεπιστήμιο Ιωαννίνων. Σχολή Θετικών Επιστημών. Τμήμα Χημείας
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Elemes, Y.
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Intermolecular primary and secondary isotope effects on the ene reaction of N-phenyl-1,2,4-triazoline-3,5-dione (PTAD) and singlet oxygen (O-1(2)) with deuterium-substituted (E)-2-methylbuten-2-oic (tiglic) acid methyl esters have been determined. In the case Of O-1(2), the primary isotope effect is 1.30-1.49 and the alpha and beta-secondary isotope effects are near unity, consistent with a stepwise reaction path via a perepoxide intermediate, where the allylic hydrogen-abstraction step is rate determining. On the other hand, the existence of both primary (1.44) and inverse alpha and beta-secondary isotope effects (0.91 and 0.77, respectively) in the PTAD reaction is consistent with either a concerted or a stepwise mechanism. Experiments in which both intermolecular primary and secondary isotope effects were measured at the same time suggest that, like singlet oxygen, PTAD reacts in a stepwise manner with the formation of the aziridinium imide intermediate (AI) in the rate-determining-step.
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