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Formal organocatalítico asimétrico [3 + 2] cicloadición con nitronas de N-carbamoil generadas in situ

Claudio Gioia¹, Francesco Fini, Andrea Mazzanti

¹Department of Organic Chemistry A. Mangini, University of Bologna, viale Risorgimento 4, 40136 Bologna, Italy.

Journal of the American Chemical Society

|June 26, 2009

Resumen

Este estudio introduce una nueva reacción organocatalítica para sintetizar isoxazolidinas protegidas por N-Boc y N-Cbz. El método utiliza catalizadores fácilmente disponibles y proporciona bloques de construcción químicos valiosos con alto rendimiento y pureza.

Área de la Ciencia:

Química orgánica es la química orgánica.
Catalización asimétrica por catálisis asimétrica.
Metodología sintética de la metodología sintética.

Sus antecedentes:

Los nitrones N-carbamoil son típicamente difíciles de generar y utilizar como 1,3-dipolos.
La síntesis asimétrica de las isoxazolidinas es crucial para acceder a valiosos bloques de construcción quirales.

Objetivo del estudio:

Desarrollar una nueva reacción de cicloadición formal [3 + 2] organocatalítica.
Para lograr la síntesis directa de isoxazolidinas protegidas por N-Boc y N-Cbz con alta diastereoselectividad y enantioselectividad.

Principales métodos:

Generación in situ de nitrones de N-carbamoil.
Organocatálisis utilizando sales de amonio cuaternario cuaternario del alcaloide Cinchona.
Formal [3 + 2] cicloadición con glutaconatos como dipolarófilos.

Principales resultados:

Síntesis directa de isoxazolidinas protegidas por N-Boc y N-Cbz como diastereoisómeros individuales.
Generalmente altos rendimientos y excesos enantioméricos alcanzados bajo condiciones suaves.
Utilidad sintética demostrada de los productos en isoxazolidinas libres, aminoalcoholes y lactamas.

Conclusiones:

Este trabajo es pionero en el uso de nitrones N-carbamoil como dipolos 1,3-pobre en electrones en la catálisis asimétrica.
El método desarrollado ofrece una ruta eficiente a valiosos derivados quirales de isoxazolidina.
El sistema catalítico se basa en derivados de alcaloides de Cinchona baratos y fácilmente disponibles.

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