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La cloración alfa asimétrica organocatalítica directa de los aldehídos

Nis Halland¹, Alan Braunton, Stephan Bachmann

¹Danish National Research Foundation, Center for Catalysis, Department of Chemistry, Aarhus University, DK-8000 Aarhus C, Denmark.

Journal of the American Chemical Society

|April 15, 2004

Resumen

Un nuevo método permite la cloración alfa enantioselectiva de aldehídos mediante organocatálisis. Este eficiente proceso produce valiosos intermediarios quirales para la síntesis de moléculas complejas como los aminoácidos.

Área de la Ciencia:

Química orgánica es la química orgánica.
Catalización asimétrica por catálisis asimétrica.

Sus antecedentes:

Los alfa-cloro aldehídos quirales son valiosos bloques de construcción sintéticos.
Desarrollar métodos enantioselectivos para su síntesis sigue siendo un desafío.

Objetivo del estudio:

Desarrollar una cloruración alfa enantioselectiva organocatalítica directa de los aldehídos.
Para demostrar la utilidad sintética de los resultantes aldehídos quirales alfa-cloro.

Principales métodos:

Utilizó N-clorosuccinimida (NCS) como fuente de cloro.
Se emplean organocatalizadores fácilmente disponibles como la amida de L-prolina y la (2R,5R) -difenilpirrolidina.
Investigó la transformación de los aldehídos alfa-cloro en alcoholes, epóxidos, aminoalcoholes y ésteres.

Principales resultados:

Se han logrado altos rendimientos (hasta el 99%) y enantioselectividades (hasta el 95% ee) para alfa-cloro aldehídos.
Se ha demostrado una conversión eficiente a alcoholes alfa-cloro, epoxidos y aminoalcoholes sin pérdida de pureza óptica.
Sintetizó ésteres alfa-cloro ópticamente activos y los convirtió en aminoácidos no proteinogénicos con altos rendimientos y conservó el exceso enantiomérico.

Conclusiones:

Se estableció un método organocatalítico robusto y eficiente para la cloración alfa enantioselectiva de aldehídos.
Demostró la amplia aplicabilidad sintética de los aldehídos quirales alfa-cloro en la construcción de moléculas quirales complejas.
Destacó el potencial para sintetizar valiosos aminoácidos no proteinogénicos a partir de estos productos intermedios.

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