Conformational preferences of methacrolein in Diels-Alder and 1,3-dipolar cycloaddition reactions.
J Org Chem
; 71(26): 9831-40, 2006 Dec 22.
Article
en En
| MEDLINE
| ID: mdl-17168603
A 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.
Buscar en Google
Colección:
01-internacional
Base de datos:
MEDLINE
Asunto principal:
Acroleína
/
Simulación por Computador
Tipo de estudio:
Prognostic_studies
Idioma:
En
Revista:
J Org Chem
Año:
2006
Tipo del documento:
Article
País de afiliación:
España
Pais de publicación:
Estados Unidos