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Con respecto a la reactividad de los dioxiranos. Observaciones de experimentos y teoría de la teoría

Cosimo Annese¹, Lucia D'Accolti, Anna Dinoi

¹Dipartimento Chimica, Università di Bari, CNR.-ICCOM, v. Amendola 173, I-70126 Bari, Italy.

Journal of the American Chemical Society

|January 8, 2008

Resumen

Los dioxiranos exhiben reactividad electrófila, incluso con los alquenos pobres en electrones, desafiando hipótesis anteriores. El metil ((trifluorometil) dioxirano es un oxidante electrofílico más fuerte que el dimetildioxirano, apoyado por datos electroquímicos.

Área de la Ciencia:

Química orgánica es la química orgánica.
Mecanismos de reacción Mecanismos de reacción
Química de la oxidación Química de la oxidación

Sus antecedentes:

Los dioxiranos son potentes oxidantes en la síntesis orgánica.
La naturaleza electrónica de los alquenos en la epoxidación del dioxirano sigue siendo objeto de investigación.
Se ha debatido una reactividad "bifílica" propuesta (electrofílica vs. nucleófila) para los dioxiranos.

Objetivo del estudio:

Investigar experimentalmente la reactividad de los dioxiranos con los alquenos pobres en electrones.
Para determinar el carácter electrónico preciso de la epoxidación de dioxirano.
Para comparar el poder oxidante de diferentes dioxiranos.

Principales métodos:

Estudios cinéticos utilizando los valores de Hammett rho para los cinnamonitriles sustituidos.
Análisis electroquímico a través de voltametría cíclica para medir potenciales de reducción.
Frontier Molecular Orbital (FMO) teoría para racionalizar las diferencias de reactividad.

Principales resultados:

Los datos experimentales refutan la hipótesis "bifílica", confirmando el ataque electrófilo a los alquenos pobres en electrones.
Los valores rho de Hammett demuestran inequívocamente la epoxidación electrofílica.
El metil ((trifluorometil) dioxirano (TFDO) muestra un mayor poder oxidante electrofílico que el dimetildioxirano (DDO).
Los potenciales de reducción se correlacionan con las diferencias observadas en la fuerza oxidante.

Conclusiones:

Los dioxiranos actúan constantemente como oxidantes electrófilos, independientemente de las propiedades electrónicas de los alquenos.
El TFDO es un oxidante electrofílico más potente que el DDO.
La teoría FMO proporciona un marco para comprender la reactividad mejorada de TFDO.

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