Enolizaciones estereoselectivas mediadas por magnesio y bisamidas de calcio: comportamiento de agregación
Xuyang He1, John F Allan, Bruce C Noll
1Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556, USA.
Journal of the American Chemical Society
|May 12, 2005
Resumen
Las bases de magnesio y calcio bis ((hexamethyldisilazide) muestran Z-selectividad en disolventes polares para la enolización de cetonas. Sin embargo, los sistemas de magnesio favorecen a los E-enolatos en soluciones de areno, formando equilibrios monómero-dimero.
Área de la Ciencia:
- Química organometálica de las sustancias orgánicas.
- Síntesis estereoselectiva por síntesis estereoselectiva.
- La enolización de cetonas por enolización.
Sus antecedentes:
- Los complejos metálicos bis ((hexametildisilazida) son bases potentes.
- La comprensión de los intermediarios enolados metálicos es crucial para las reacciones estereoselectivas.
Objetivo del estudio:
- Para evaluar el magnesio y el calcio bis ((hexamethyldisilazide) para la enolización estereoselectiva de cetonas.
- Para dilucidar las propiedades estructurales y electrónicas de los metales enolados intermedios.
Principales métodos:
- Reacciones de la propiofenona con el magnesio y el calcio bis ((hexamethyldisilazide).
- Monitoreo in situ mediante el uso de espectroscopia de RMN.
- Los experimentos de captura de éter de enol silílico.
- Análisis cristalográfico de complejos de enolados metálicos.
Principales resultados:
- Ambas bases exhiben selectividad Z en disolventes polares.
- Los sistemas de magnesio muestran preferencia por el enolato E en soluciones de areno, con equilibrios monómero-dimérico observados.
- Los datos cristalográficos revelaron una disolución de un dimer.enolado de amidomagnesio disuelto.
- Los sistemas de calcio mostraron un comportamiento distinto, formando pares de iones separados por disolventes y enolados de amidocalcio monoméricos.
Conclusiones:
- La elección del disolvente y el metal influyen significativamente en la estereoselectividad y la estructura de los enolados metálicos.
- El magnesio y el calcio (bis ((hexamethyldisilazide) ofrecen reactividad sintonizable para la enolización de cetonas.
- Se obtuvieron conocimientos estructurales detallados sobre los intermediarios de enolados metálicos.
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