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Mecanismos de la estereoinversión del aleno por complejos de imidozirconio

Forrest E Michael¹, Andrew P Duncan, Zachary K Sweeney

¹Department of Chemistry and Center for New Directions in Organic Synthesis, University of California at Berkeley, Berkeley, California 94720, USA.

Journal of the American Chemical Society

|June 12, 2003

Resumen

Este estudio explora la estereoinversión mediada por zirconio en alenos utilizando metaciclos. Los investigadores observaron productos intermedios y propusieron mecanismos para las transformaciones estereoquímicas en estos compuestos organometálicos.

Área de la Ciencia:

Química organometálica Química orgánica de los metales.
La estereoquímica es la estereoquímica.
Química del zirconio Química del zirconio

Sus antecedentes:

Los Allenes son compuestos orgánicos versátiles con una reactividad única.
El control estereoquímico en la síntesis orgánica es crucial para el desarrollo de nuevas moléculas.
Los complejos de circonoceno son reactivos valiosos en las transformaciones orgánicas.

Objetivo del estudio:

Para investigar el comportamiento estereoquímico de los metaciclos mediados por zirconio derivados de los alenos.
Para dilucidar los mecanismos de estereoinversión en estos intermedios organometálicos.
Comprender la influencia de los diferentes sustituyentes de aleno en el resultado estereocímico.

Principales métodos:

[2 + 2] reacciones de cicloadición entre alenos enriquecidos con enantio y complejos de imidozirconoceno.
Medición de las tasas de racemización del ciclo metálico utilizando espectroscopia de dicroísmo circular.
Observación de los intermediarios de reacción a través de la espectroscopia de resonancia magnética nuclear (RMN).

Principales resultados:

Se midieron con éxito las tasas de racemización relativa de los metaciclos.
Se identificaron intermediarios en la estereoinversión del difenilalleno.
Se establecieron distintos mecanismos propuestos para la racemización del ciclo metálico del dialquilalleno y el diarilaleno.

Conclusiones:

La estereoinversión de los alenos puede ser efectivamente mediada por complejos de zirconio.
Es probable que los metaciclos derivados de los dialquilalenos se racemicen a través de la eliminación del beta-hidruro.
La estereoinversión de los metaciclos derivados del diarilaleno es más lenta y puede implicar un estado de transición eta4-azatrimetilenometano.

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