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A DFT study of the molecular mechanisms of the nucleophilic addition of ester-derived lithium enolates and silyl ketene acetals to nitrones: Effects of the lewis acid catalyst

AuthorsDomingo, Luis R.; Arnó, Manuel; Merino, Pedro ; Tejero, Tomás
Density functional calculations
Nucleophilic addition
Reaction mechanisms
Issue DateMay-2006
CitationEuropean Journal of Organic Chemistry (15): 3464-3472 (2006)
AbstractThe molecular mechanisms for the nucleophilic addition of lithium enolates and silyl ketene acetals to nitrones in the absence and in the presence of a Lewis acid (LA) catalyst to give isoxazolidin-5-ones or hydroxylamines have been investigated by DFT methods at the B3LYP/6-31G* level. The addition of lithium enolates to nitrones gives the corresponding hydroxylamines, while the addition of silyl ketene acetals affords isoxazolidin-5-ones through a concerted 1,3-dipolar cycloaddition. The addition of the silyl ketene acetals to LA-coordinated nitrones yields isoxazolidin-5-ones by a polar concerted cycloaddition or a stepwise nucleophilic attack via zwitterionic intermediates. A silyl migration on the [3+2] cycloadduct yields the corresponding O-silylhydroxylamine. An analysis of the global electrophilicity of the reagents accounts for the strong electrophile activation of the LA-coordinated nitrone, and the analysis of the local indices leads to an explanation for the experimentally observed regioselectivity.
Description9 pages, 6 schemes, 3 figures, 2 tables.
Publisher version (URL)http://dx.doi.org/10.1002/ejoc.200600105
Appears in Collections:(ICMA) Artículos
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