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Reglas para el cierre del anillo aniónico y radical de los alquinos
Igor V Alabugin1, Kerry Gilmore, Mariappan Manoharan
1Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida, 32306-4390, United States. alabugin@chem.fsu.edu
Journal of the American Chemical Society
|June 17, 2011
Resumen
Este estudio hace una revisión de Baldwin.
Área de la Ciencia:
- Química orgánica es la química orgánica.
- Mecanismos de reacción Mecanismos de reacción
- La estereoquímica es la estereoquímica.
Sus antecedentes:
- Las reglas de Baldwin predicen modos de ciclización favorecidos basados en el tamaño del anillo y la trayectoria de ataque.
- Se vuelven a examinar los factores estereoelectrónicos que rigen las ciclizaciones nucleófilas y radicales de los alquinos.
Objetivo del estudio:
- Reevaluar la base estereoelectrónica de las trayectorias de ataque favorecidas en las ciclizaciones de alquinos.
- Para comparar las preferencias estereoelectrónicas intrínsecas con la estabilidad termodinámica en la formación de productos.
Principales métodos:
- Dissección de las barreras de activación en componentes intrínsecos y termodinámicos utilizando la teoría de Marcus.
- Análisis computacional de las selectividades de ciclización para varios nucleófilos.
- Comparación con observaciones experimentales de reacciones de ciclización conocidas.
Principales resultados:
- Las trayectorias de ataque obtusas (exo-dig) son estereoelectrónicamente favorecidas sobre las trayectorias agudas (endo-dig) para la formación de enlaces intrínsecos.
- La estabilidad termodinámica de los endoproductos puede enmascarar la preferencia intrínseca por anillos más pequeños.
- Las predicciones se alinean con los datos experimentales para ciclizaciones de 3 exo dígitos y 4 exo dígitos, contradiciendo las reglas de Baldwin.
- Las selectividades calculadas para los nucleófilos centrados en el carbono, el nitrógeno y el oxígeno muestran preferencia exo-digital.
Conclusiones:
- La preferencia estereoelectrónica intrínseca favorece los cierres exo-dig, desafiando las reglas tradicionales de Baldwin.
- Los factores termodinámicos juegan un papel importante, especialmente en la formación de anillos más pequeños.
- Los hallazgos proporcionan un modelo estereoelectrónico más preciso para las ciclizaciones de alquinos, aplicable tanto a las vías nucleófilas como a las radicales.
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