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La alilación regio y enantioselectiva catalizada por iridio de los enolados cetónicos
Timm Graening1, John F Hartwig
1Department of Chemistry, Yale University, P.O. Box 208107, New Haven, Connecticut 06520-8107, USA.
Journal of the American Chemical Society
|December 8, 2005
Resumen
Este estudio introduce un nuevo método para crear cetonas ramificadas gamma, delta-insaturadas usando catalizadores de iridio. El proceso logra una alta regioselectividad y enantioselectividad, ofreciendo una valiosa ruta a moléculas orgánicas complejas.
Área de la Ciencia:
- Química orgánica es la química orgánica.
- La catálisis es la catálisis.
- Síntesis asimétrica de síntesis.
Sus antecedentes:
- La síntesis enantioselectiva de moléculas orgánicas complejas sigue siendo un desafío significativo en la química sintética.
- La alición alfa de los enolados cetónicos es una transformación clave para la construcción de enlaces carbono-carbono.
- El desarrollo de sistemas catalíticos eficientes para la alilación regio y enantioselectiva es crucial.
Objetivo del estudio:
- Informar de una nueva alfa-alilación regio- y enantioselectiva de enolados cetónicos no estabilizados.
- Para sintetizar cetonas gamma ramificadas y delta insaturadas de materiales de partida fácilmente disponibles.
- Desarrollar un sistema catalítico eficiente utilizando complejos metalacíclicos de iridio.
Principales métodos:
- Se utilizaron catalizadores de iridio metalacíclicos para la reacción de aliado alfa.
- Se emplean éteres de sililenoles y alcoholes alílicos protegidos por Boc como sustratos.
- Condiciones de reacción optimizadas utilizando fluoruro de cesio (CsF) y fluoruro de zinc (ZnF2) como promotores.
- Investigaron los complejos de iridio derivados de los ligandos de la fosforamidita.
Principales resultados:
- Se lograron elevadas regioselectividades y enantioselectividades (91-96% ee) para los productos de sustitución ramificada.
- Se ha demostrado la supresión de los subproductos de la diyalización a través del uso de CsF y ZnF2.2.
- Se identificó la formación in situ de un precatalizador Ir ciclometalizado.
- Aplicó con éxito el método a diez ejemplos de sustratos aromáticos y alifáticos.
Conclusiones:
- Desarrolló un método eficiente y selectivo para la síntesis enantioselectiva de cetonas ramificadas gamma, delta-insaturadas.
- El proceso reportado catalizado por iridio proporciona una valiosa alternativa a los métodos tradicionales como los reordenamientos de Claisen para acceder a compuestos bifuncionales.
- Esta metodología ofrece una nueva vía para la síntesis asimétrica de moléculas orgánicas sintéticamente importantes.
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