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Intramolecular sin precedentes [4 + 2]-Cicloadición entre un 1,3-Diene y un Diazo Ester

Huang Qiu^1,2,3, Harathi D Srinivas¹, Peter Y Zavalij²

¹Department of Chemistry, The University of Texas at San Antonio , San Antonio, Texas 78249, United States.

Journal of the American Chemical Society

|January 23, 2016

Resumen

Este estudio introduce una nueva reacción de [4 + 2]-cicloadición utilizando compuestos diazo y dienos. El proceso, iniciado por la reorganización catalizada por el oro, se produce en condiciones suaves con altos rendimientos.

Área de la Ciencia:

Química orgánica
Reacciones de cicloadición

Sus antecedentes:

Los compuestos diazo se someten típicamente a reacciones de [3 + 2]-cicloadición.
El descubrimiento de nuevas vías de cicloadición expande las capacidades sintéticas.

Objetivo del estudio:

Explorar y caracterizar una reacción de cicloadición [4 + 2] previamente desconocida que involucra compuestos diazo.
Investigar el mecanismo y el alcance de esta nueva transformación.

Principales métodos:

Rearreglo catalizado por oro de los arildiazoacetatos de propargilo a los arildiazoacetatos de 1,3-dienilo activados.
Reacciones de cicloadición térmica de E- y Z-1,3-dienil aryldiazoacetatos aislados con dienos.
Estudios cinéticos y análisis de Hammett para elucidar el mecanismo de reacción.

Principales resultados:

Demostración exitosa de una nueva reacción de cicloadición térmica [4 + 2] entre los 1,3-dienilarildiazoacetatos activados y los dienos.
Se obtuvieron altos rendimientos y condiciones de reacción suaves para la [4 + 2]-cicloadición.
El isómero E del dienil diazoacetato sufre fácilmente cicloadición, mientras que el isómero Z no es reactivo.
Se determinaron los parámetros cinéticos (ΔH(‡) = 15,6 kcal/mol, ΔS(‡) = -27,3 cal/(mol·°C)) para la reacción del isómero E.
Las relaciones de Hammett indicaron un carácter dipolar para la transformación.

Conclusiones:

Este trabajo presenta el primer ejemplo de una reacción de [4 + 2]-cicloadición que involucra compuestos diazo y dienos.
La reacción ofrece una nueva ruta sintética bajo condiciones suaves y eficientes.
La estereoselectividad en la cicloadición está influenciada por la geometría del dienil diazoacetato.

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