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Título

Conformational Preferences of Methacrolein in Diels−Alder and 1,3-Dipolar Cycloaddition Reactions

AutorBarba, Carmen ; Carmona, Daniel ; García, José I. ; Lamata, M. Pilar ; Mayoral, José A. ; Salvatella, Luis ; Viguri, Fernando
Fecha de publicación1-dic-2006
EditorAmerican Chemical Society
CitaciónThe Journal of Organic Chemistry 71(26): 9831–9840 (2006)
ResumenA B3LYP/6-31G* study has been carried out for the reactions of methacrolein with cyclopentadiene, parent nitrone, 1-pyrroline-1-oxide, and (Z)-C,N-diphenylnitrone, in which the coordination of a Lewis acid (borane) and the solvent polarity (dichloromethane) have been taken into account. Calculated activation parameters, regioselectivities (for 1,3-dipolar cycloaddition reactions), and endo/exo stereoselectivities show good agreement with available experimental data. Gas-phase calculations show a varied behavior of the s-cis/s-trans TS stability for noncatalyzed reactions (from the systematic s-cis preference for the cyclopentadiene reaction to the systematic s-trans predilection encountered in the diphenylnitrone cycloaddition). BH3 coordination leads to a preferential stabilization of s-trans TSs in the reactions of cyclopentadiene (exo approach) and diphenylnitrone but a larger stabilization of s-cis structures in the processes involving the parent nitrone or 1-pyrroline-1-oxide. Additionally, a rather systematic preferential stabilization of s-trans structures is induced by solvent polarity in most reactions. As a consequence, an s-trans preference is predicted in solution for both thermal and catalyzed types of reactions in most approaches. Such a conclusion is consistent with some experimental results suggesting a preference for a particular conformation of the methacrolein−Lewis acid complexes.
Descripción10 pages, 4 figures, 4 tables.
Versión del editorhttp://dx.doi.org/10.1021/jo062200k
URIhttp://hdl.handle.net/10261/19323
DOI10.1021/jo062200k
ISSN1520-5126
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