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Ligandos NHC adaptados para el control regional y enantio simultáneo en acoplamientos reductores catalizados por
Hengbin Wang1, Gang Lu2, Grant J Sormunen1
1Department of Chemistry, University of Michigan , 930 North University Avenue, Ann Arbor, Michigan 48109-1055, United States.
Journal of the American Chemical Society
|June 17, 2017
Resumen
Una nueva clase de ligandos N-heterocíclicos enantiopuros (NHC) permite reacciones altamente selectivas catalizadas por níquel. Estos ligandos controlan tanto la regioselectividad como la enantioselectividad en las reacciones de acoplamiento de aldehídos con alquinas y alenos.
Área de la Ciencia:
- Química orgánica
- Catálisis
- Síntesis asimétrica
Sus antecedentes:
- En trabajos anteriores se utilizaron ligandos de carbenos N-heterocíclicos (NHC) racémicos.
- Se carecía de una ruta escalable a los ligandos NHC enantiopuros.
- Los ligandos altamente obstaculizados son cruciales para las transformaciones catalíticas desafiantes.
Objetivo del estudio:
- Desarrollar una síntesis escalable de ligandos NHC enantiopuros.
- Para establecer reacciones de acoplamiento reductor enantioselectivo catalizadas por níquel utilizando estos ligandos.
- Investigar la capacidad de los ligandos para controlar la regioselectividad y la enantioselectividad.
Principales métodos:
- Buchwald-Hartwig N,N-diarilación para la síntesis de ligandos.
- Acoplamiento reductor enantioselectivo catalizado por níquel de aldehídos con alquinas.
- Extensión de la metodología para incluir aldehídos y alenos.
- Estudios computacionales para aclarar los mecanismos de reacción y las propiedades de los ligandos.
Principales resultados:
- Se logró una ruta escalable y práctica para los ligandos NHC enantiopuros excepcionalmente obstaculizados.
- El acoplamiento reductor enantioselectivo catalizado por níquel de aldehídos y alquinos produjo derivados de alcohol alílico con alta regio- (> 95:5) y enantioselectividad (hasta 94% ee).
- La metodología se extendió a los aldehídos y a los alenos, produciendo alcoholes alilicos protegidos por sililo.
- El volumen estérico de ligandos permitió obtener resultados regioquímicos complementarios en comparación con los métodos anteriores.
- El análisis computacional explicó el origen del obstáculo estérico, la enantioselectividad y las interacciones de reacción clave.
Conclusiones:
- Los ligandos NHC enantiopuros desarrollados son altamente eficaces para controlar la regioselectividad y la enantioselectividad en reacciones catalizadas por níquel.
- Las propiedades estéricas de estos ligandos son clave para lograr una alta selectividad, incluso con sustratos difíciles.
- Este trabajo proporciona una nueva herramienta valiosa para la síntesis asimétrica, particularmente para la construcción de derivados complejos de alcohol alílico.
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