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Isotope Effects Reveal an Alternative Mechanism for "Iminium-Ion" Catalysis.

ABSTRACT: A novel mechanism for the epoxidation of enals with hydrogen peroxide catalyzed by diarylprolinol silyl ether supported by experimental 13C kinetic isotope effects (KIEs) and density functional theory calculations is presented. Normal 13C KIEs, measured on both the carbonyl- and ?-carbon atoms of the enal, suggest participation of both carbon atoms in the rate-determining step. Calculations show that the widely accepted iminium-ion mechanism does not account for this experimental observation. A syn-SN2' substitution mechanism, which avoids formation of a discrete iminium-ion intermediate, emerges as the most likely mechanism based on agreement between experimental and predicted KIEs.

SUBMITTER: Izzo JA

PROVIDER: S-EPMC6238210 | biostudies-literature | 2018 Jul

REPOSITORIES: biostudies-literature

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Isotope Effects Reveal an Alternative Mechanism for "Iminium-Ion" Catalysis.

Izzo Joseph A JA Poulsen Pernille H PH Intrator Jeremy A JA Jørgensen Karl Anker KA Vetticatt Mathew J MJ

Journal of the American Chemical Society 20180629 27

A novel mechanism for the epoxidation of enals with hydrogen peroxide catalyzed by diarylprolinol silyl ether supported by experimental <sup>13</sup>C kinetic isotope effects (KIEs) and density functional theory calculations is presented. Normal <sup>13</sup>C KIEs, measured on both the carbonyl- and β-carbon atoms of the enal, suggest participation of both carbon atoms in the rate-determining step. Calculations show that the widely accepted iminium-ion mechanism does not account for this experi ...[more]

PMID: 29940119

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