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Hidrogenaciones altamente diastereoselectivas que conducen a beta-hidroxi delta-lactonas en forma protegida por
Svante Brandänge1, Magnus Färnbäck, Hans Leijonmarck
1Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, SE-106 91, Stockholm, Sweden. svante@organ.su.se
Journal of the American Chemical Society
|September 25, 2003
Resumen
La hidrogenación de delta-lactonas insaturadas sobre catalizadores de paladio produce lactonas saturadas con una alta diastereoselectividad. El análisis conformacional revela diversas estructuras de anillos más allá de los modelos previamente aceptados.
Área de la Ciencia:
- Química orgánica es la química orgánica.
- La estereoquímica es la estereoquímica.
- Química computacional es la química computacional.
Sus antecedentes:
- La hidrogenación catalizada por paladio es una reacción clave en la síntesis orgánica.
- Comprender los resultados estereoquímicos de la hidrogenación es crucial para controlar la arquitectura molecular.
- Las delta-lactonas son importantes motivos estructurales en productos naturales y productos farmacéuticos.
Objetivo del estudio:
- Para investigar el control estereoquímico en la hidrogenación catalizada por el paladio de las delta-lactonas alfa, beta insaturadas sustituidas.
- Desarrollar una generalización estereoquímica para la hidrogenación de las 1-oxa-3-ciclohexeno-2-onas trans-5,6-disubstituidas.
- Explorar el paisaje conformacional de las delta-lactonas saturadas utilizando métodos experimentales y computacionales.
Principales métodos:
- Hidrogenación de éteres de enol MEM y acetatos de enol utilizando paladio sobre carbono (Pd/C).
- Análisis de datos cristalográficos de rayos X para 67 compuestos de delta-lactona saturados.
- Cálculos ab initio (HF/6-31G) para determinar las energías conformacionales y los estados de transición.
Principales resultados:
- La hidrogenación de éteres de enol MEM y acetatos de enol procedió con una diastereoselectividad muy alta (>99%) a delta-lactonas saturadas.
- Se formuló una regla estereoquímica: trans-5,6-disubstituido 1-oxa-3-ciclohexeno-2-ones hidrogenado desde el trans lateral al C(6) -sustituto.
- El análisis de conformación reveló una diversidad significativa en las delta-lactonas saturadas, con múltiples conformadores accesibles (media silla, barco, silla, sobre, sesgo) dentro de un rango de energía estrecho.
Conclusiones:
- La hidrogenación catalizada por paladio ofrece un excelente control estereoquímico para la síntesis de delta-lactonas saturadas.
- El comportamiento conformacional de las delta-lactonas saturadas es más complejo de lo que se pensaba anteriormente, ya que implica una gama más amplia de formas accesibles.
- Los hallazgos proporcionan una comprensión mecanicista de la estereoselectividad y amplían el paradigma conformacional de las delta-lactonas.
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