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El postulado de Hammond permite el enriquecimiento enantiomérico de compuestos de fósforo a través de dos procesos
Kamalraj V Rajendran1, Kirill V Nikitin1, Declan G Gilheany1
1Centre for Synthesis and Chemical Biology, School of Chemistry, University College Dublin, Belfield, Dublin 4, Ireland.
Journal of the American Chemical Society
|July 18, 2015
Resumen
Este estudio revela un método de resolución cinética para los compuestos de fósforo. Las sales de alkoxifosfonio diastereoméricas se enriquecen a sí mismas durante la descomposición, aumentando el exceso enantiomérico en los productos finales hasta un 97%.
Área de la Ciencia:
- Química orgánica
- Estereoquímica
- Espectroscopia
Sus antecedentes:
- Las fosfinas terciarias y los óxidos de fosfina son cruciales en la síntesis orgánica.
- El control de la estereoselectividad en la química del fósforo es un desafío.
- La resolución dinámica ofrece un camino hacia una alta pureza enantiomérica.
Objetivo del estudio:
- Investigar la resolución dinámica de las fosfinas terciarias y los óxidos de fosfina.
- Comprender los pasos que determinan la estereoselectividad en la formación y descomposición de los intermedios.
- Desarrollar un método para obtener un alto exceso enantiomérico (ee) en los productos de fósforo.
Principales métodos:
- Se utilizó la espectroscopia de resonancia magnética nuclear (RMN), específicamente la RMN (31) P, para controlar las reacciones.
- Se sintetizaron y analizaron sales de alkoxifosfonio diastereomérico (DAPS).
- Se realizaron experimentos de captura reductora utilizando litio tri-sec-butilborohidrido (L-Selectride) en varios momentos.
Principales resultados:
- La estereoselectividad se establece durante la formación de DAPS, limitando el exceso enantiomérico posterior.
- (31) La monitorización por RMN reveló un autoenriquecimiento diastereomérico espontáneo durante la descomposición de DAPS.
- Se observó un exceso enantiomérico progresivamente mayor de productos de fosfina con tiempos de reacción más largos.
- Se alcanzó una eficiencia energética de hasta el 97% para los productos finales de fósforo.
Conclusiones:
- La descomposición de DAPS exhibe un autoenriquecimiento diastereomérico, favoreciendo al diastereómero menor.
- El postulado de Hammond probablemente rige tanto la formación de DAPS como la cinética de descomposición.
- Esta mejora cinética de la resolución cinética proporciona una ruta efectiva a los compuestos de fósforo altamente enriquecidos enantioméricamente.
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