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Construcción de múltiples estereocentros cuaternarios contiguos en moléculas acíclicas por litio-borilación
Charlotte G Watson1, Angelica Balanta, Tim G Elford
1School of Chemistry, University of Bristol , Cantock's Close, Bristol, BS8 1TS, U.K.
Journal of the American Chemical Society
|December 4, 2014
Resumen
Un nuevo método que utiliza boranos mezclados permite la síntesis de centros estereogénicos cuaternarios adyacentes, superando las limitaciones de la borilación estándar para los sistemas obstaculizados. Este poderoso enfoque crea cadenas de carbono complejas con un alto control estéreo.
Área de la Ciencia:
- Química orgánica es la química orgánica.
- Síntesis estereoselectiva de síntesis.
Sus antecedentes:
- La litiación del carbamato seguida de la berilación es un método clave para la homologación del reactivo de boro.
- Este método estándar se enfrenta a desafíos con sustratos estéricamente obstaculizados, particularmente en la construcción de centros cuaternarios.
Objetivo del estudio:
- Desarrollar un método robusto para sintetizar centros estereogénicos cuaternarios adyacentes en sistemas obstaculizados.
- Para lograr un control estéreo completo en la construcción de cadenas de carbono complejas.
Principales métodos:
- Se utilizan boranos mixtos (tBuBMe2) para la borilación de carbamatos secundarios obstaculizados.
- Desarrolló un procedimiento de una sola olla para la homologación secuencial, lo que permite la creación de múltiples centros cuaternarios contiguos.
- Los boranos resultantes se convierten en alcoholes terciarios o aminas C-terciarias mediante tratamiento con cloramina.
- Empleó métodos computacionales para investigar el origen de la estereoselectividad.
Principales resultados:
- Sintetizó con éxito centros estereogénicos cuaternarios adyacentes con control estereogénico completo utilizando boranos mixtos, superando el fracaso de los ésteres tBu-borónicos estándar.
- Demostró la capacidad de repetir el proceso en una olla, dando cadenas de carbono con múltiples centros estereogénicos cuaternarios contiguos.
- Se logró una alta selectividad para la migración de grupos alquilo sobre la migración de grupos metilo, como lo confirmó el análisis computacional.
- Convirtió eficientemente los boranos sintetizados en valiosas funcionalidades de alcohol terciario y aminas C-terciarias.
Conclusiones:
- Los boranos mixtos ofrecen una alternativa superior a los ésteres borónicos estándar para la síntesis estereoselectiva de centros cuaternarios obstaculizados.
- El protocolo desarrollado de una sola olla y varios pasos proporciona un acceso eficiente a andamios de carbono complejos con múltiples estereocentros.
- Las ideas computacionales aclaran el mecanismo y la selectividad del paso clave de la migración de alquilo.
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