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Reacciones estereodivergentes SN2@P de las oxazafosfolidinas de boro: estudios experimentales y teóricos
Hester Zijlstra1, Thierry León, Abel de Cózar
1Department of Theoretical Chemistry, Amsterdam Center for Multiscale Modeling, VU University Amsterdam, De Boelelaan 1083, NL-1081 HV Amsterdam, The Netherlands.
Journal of the American Chemical Society
|February 27, 2013
Resumen
La apertura de anillos estereodivergentes de oxazafosfolidinas con reactivos de litio alquilo ofrece una nueva ruta a los compuestos quirales de fósforo. Este método permite la síntesis de ambos enantiómeros de los principales intermediarios P-esteroégenos a partir de un único auxiliar.
Área de la Ciencia:
- Química orgánica es la química orgánica.
- Química de los organofosforados Química de los organofosforados
- La estereoquímica es la estereoquímica.
Sus antecedentes:
- Las oxazafosfolidinas son versátiles intermediarios en la química de los organofosforados.
- El control de la estereoquímica en el centro de fósforo es crucial para la síntesis de moléculas quirales.
- Estudios previos han demostrado resultados estereocímicos variados en las reacciones de apertura de anillos de oxazafosfolidina.
Objetivo del estudio:
- Para investigar la apertura estereodivergente del anillo de 2-fenilo oxazafosfolidinas utilizando reactivos de litio alquilo.
- Para dilucidar el mecanismo que controla el resultado estereoquímico (inversión frente a la retención) en el centro de fósforo.
- Para demostrar la síntesis de ambos enantiómeros de los intermediarios P-estero-génicos a partir de un solo aminoalcohol auxiliar.
Principales métodos:
- Reacciones estereoselectivas de apertura de anillos de N-H y N-Me oxazafosfolidinas con reactivos de litio alquilo.
- Síntesis de oxazafosfolidinas utilizando los auxiliares de aminoalcoholes quirales ((+) -cis-1-amino-2-indanol y (-) -norefedrina).
- Cálculos de la Teoría Funcional de Densidad (DFT) para modelar mecanismos de reacción y estados de transición.
Principales resultados:
- Las oxazafosfolidinas N-H se someten a una apertura de anillo altamente estereoselectiva con inversión de configuración en el fósforo.
- Las oxazafosfolidinas N-Me producen productos de apertura de anillo con retención de la configuración en el fósforo.
- Los estudios de DFT revelan un ataque trasero S(N) 2@P de un solo paso para sustratos N-H y un ataque frontal de dos pasos para sustratos N-Me.
- El grupo BH3 actúa como un grupo de dirección, coordinándose con el reactivo de litio.
Conclusiones:
- Se establece una estrategia sintética estereodivergente para los intermediarios P-esterogénicos.
- La elección del sustituto N (H vs. Me) dicta el resultado estereoquímico (inversión vs. retención).
- Los cálculos de DFT proporcionan una visión mecanicista de la estereoselectividad observada, destacando el papel del grupo dirigente BH3.
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