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Conjugación de ciclopropilo y aniones cetilo: ¿cuándo comienzan a desmoronarse las cosas?

J M Tanko¹, Xiangzhong Li, M'hamed Chahma

¹Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, USA. jtanko@vt.edu

Journal of the American Chemical Society

|March 21, 2007

Resumen

La reducción electroquímica de los derivados del ciclopropano revela diferentes tasas de apertura del anillo. Algunos compuestos se someten a una rápida apertura de anillos, mientras que otros exhiben tasas más lentas debido a la estabilización de resonancia, y uno muestra un mecanismo de reordenamiento único.

Área de la Ciencia:

La electroquímica es electroquímica.
Química orgánica es la química orgánica.
Mecanismos de reacción Mecanismos de reacción

Sus antecedentes:

Los derivados del ciclopropano son conocidos por sus sistemas de anillos tensados.
La reducción electroquímica ofrece una vía para estudiar la reactividad de estos sistemas de tensión.
Comprender los efectos de los sustituyentes en la apertura del anillo del ciclopropano es crucial.

Objetivo del estudio:

Para investigar la reducción electroquímica de varios derivados del 1,2-diacilciclopropano.
Para determinar la cinética y los mecanismos de apertura del anillo después de la transferencia de electrones.
Explorar los efectos de los sustituyentes sobre la estabilidad y la reactividad de los aniones radicales.

Principales métodos:

Reducción electroquímica del 1,2-diacetilciclopropano, el 1-acetil-2-fenilciclopropano, el 1-acetil-2-benzoilciclopropano y el 1,2-dibenzoilciclopropano.
Análisis cinético de la apertura del anillo de aniones radicales.
Estudios computacionales que incluyen cálculos de órbitas moleculares.

Principales resultados:

El anión radical 1-acetil-2-fenilciclopropano tiene una barrera muy pequeña para la apertura del anillo (> 10^7 s^-1).
Los ciclopropanos sustituidos por benzoilo (7 y 8) muestran una apertura del anillo más lenta (10^5-10^6 s^-1) debido a la estabilización por resonancia.
El 1,2-dibenzoilciclopropano (8) se somete a una reorganización inesperada del vinilciclopropano al ciclopenteno a través de un mecanismo de cadena de iones radicales.
Los resultados de la reducción electroquímica del 1,2-diacetilciclopropano (5) son ambiguos, lo que sugiere una simple transferencia de electrones o una transferencia de electrones disociativa concertada (DET).

Conclusiones:

Los grupos de sustitutos influyen significativamente en la vía de reducción electroquímica y la cinética de apertura del anillo de los derivados del ciclopropano.
La estabilización de la resonancia por grupos benzoilo reduce la velocidad de apertura del anillo.
Se observó un nuevo mecanismo de reordenamiento del vinilciclopropano para el 1,2-dibenzoilciclopropano.
El mecanismo de reducción para el 1,2-diacetilciclopropano sigue siendo objeto de debate, ya que podría implicar una transferencia de electrones disociativa concertada.

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