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Ciclización catalizada por el circonio altamente enantioselectiva de los aminoalquenos
Kuntal Manna1, William C Everett, George Schoendorff
1Department of Chemistry and U.S. Department of Energy Ames Laboratory, Iowa State University, Ames, Iowa 50011, USA.
Journal of the American Chemical Society
|May 2, 2013
Resumen
Las aminas N-heterocíclicas quirales se sintetizan a través de la ciclización catalítica de aminoalquenos utilizando nuevos complejos del grupo 4. Este proceso altamente enantioselectivo revela un estado de transición concertado, lo que permite una síntesis asimétrica eficiente.
Área de la Ciencia:
- Química organometálica Química orgánica de los metales.
- Catalización asimétrica por catálisis asimétrica.
- Química orgánica sintética y orgánica.
Sus antecedentes:
- El desarrollo de métodos catalíticos eficientes para sintetizar aminas quirales N-heterocíclicas es crucial para los productos farmacéuticos y la ciencia de los materiales.
- Los complejos metálicos del grupo 4 con los ligandos ciclopentadienilbis ((oxazolinyl) borato ofrecen propiedades estéricas y electrónicas únicas para la catálisis.
Objetivo del estudio:
- Investigar la ciclización catalítica de aminoalquenos utilizando nuevos complejos de ciclo-pentadienilbis (oxazolinilo) borato del grupo 4.
- Para dilucidar el mecanismo de esta transformación altamente enantioselectiva e identificar las características clave del estado de transición.
Principales métodos:
- Ciclización catalítica de varios aminoalquenos utilizando complejos de titanio, zirconio y hafnio a bajas temperaturas.
- Estudios mecánicos que emplean pruebas sintéticas, análisis cinético, efectos de isótopos cinéticos primarios y teoría de estados de transición.
- Análisis estereoquímico para determinar los excesos enantioméricos de los productos de aminas N-heterocíclicas.
Principales resultados:
- Síntesis exitosa de aminas N-heterocíclicas de cinco, seis y siete miembros con altas enantioselectividades (> 90%, hasta 99%).
- Los estudios cinéticos indicaron una interacción reversible entre el sustrato y el catalizador seguida de una etapa irreversible de ruptura del enlace N-H.
- Los parámetros de activación y los efectos del isótopo cinético apoyaron un estado de transición altamente organizado, de seis centros y concertado.
Conclusiones:
- El sistema catalítico desarrollado proporciona una ruta eficiente a las aminas N-heterocíclicas enriquecidas enantioméricamente.
- Las investigaciones mecanicistas revelaron un estado de transición concertado único responsable de la alta estereoselectividad.
- Este estudio ofrece información valiosa sobre los mecanismos asimétricos de hidroaminación / ciclización mediados por los metales del grupo 4.
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