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Reacción directa catalítica asimétrica de tipo Mannich de hidroxicetona utilizando un complejo Et2Zn/vinculado-BINOL:

Shigeki Matsunaga¹, Takamasa Yoshida, Hiroyuki Morimoto

¹Graduate School of Pharmaceutical Sciences, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.

Journal of the American Chemical Society

|July 15, 2004

Resumen

Este estudio detalla una reacción directa catalítica asimétrica de tipo Mannich utilizando un complejo BINOL vinculado al zinc. La reacción produce de manera eficiente alcoholes anti- o syn-beta-amino con alta estereoselectividad mediante el ajuste de los grupos protectores iminos.

Área de la Ciencia:

Química orgánica es la química orgánica.
Catalización asimétrica por catálisis asimétrica.
Síntesis estereoselectiva por síntesis.

Sus antecedentes:

La reacción de tipo Mannich es una reacción fundamental de formación de enlaces carbono-carbono.
El desarrollo de variantes asimétricas catalíticas es crucial para la síntesis de moléculas quirales.
Las reacciones directas catalíticas asimétricas tipo Mannich de las hidroxicetonas siguen siendo un desafío.

Objetivo del estudio:

Para describir una reacción directa catalítica asimétrica de tipo Mannich de las hidroxicetonas.
Para lograr un alto estereocontrol (anti- o sin-selectividad) utilizando un único sistema catalítico.
Para investigar la alta eficiencia del catalizador y los números de rotación.

Principales métodos:

Utilizó un complejo BINOL ligado a Et2Zn/S,S como catalizador.
Empleó diferentes grupos de protección en el nitrógeno imine (N-difenilfosfinoil (Dpp) y Boc).
Realizó estudios mecanicistas para comprender la eficiencia del catalizador.

Principales resultados:

Se obtuvieron altos rendimientos (>99%) y un excelente exceso enantiomérico (>99.5%) tanto para los alcoholes anti- como para los syn-beta-amino.
Estereoselectividad sintonizable demostrada (razones anti/syn hasta >98/2 o 5/95) mediante el cambio de grupos protectores.
Se observaron números de rotación de catalizadores significativamente altos (TON hasta 4920), reduciendo la carga del catalizador a 0.02 mol %.

Conclusiones:

El complejo BINOL ligado a Et2Zn/S,S permite una reacción de tipo Mannich catalítica asimétrica directa estereoselectiva y altamente eficiente.
La manipulación de grupo protector en la imina es clave para controlar la diastereoselectividad anti/syn.
El método desarrollado ofrece un sistema catalítico superior con TON sin precedentes para reacciones asimétricas de tipo Mannich.

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