Reacciones altamente enantioselectivas de cicloadición 1,3-dipolar de 2-benzopirilio-4-olato catalizadas por ácidos
Hiroyuki Suga1, Kei Inoue, Shuichi Inoue
1Department of Chemistry and Material Engineering, Faculty of Engineering, Shinshu University, Wakasato, Nagano 380-8553, Japan. sugahio@gipwc.shinshu-u.ac.jp
Journal of the American Chemical Society
|December 12, 2002
Resumen
Los catalizadores de ácido de Chiral Lewis, específicamente los complejos de triflato de metales de tierras raras con 2,6-bis(oxazolinyl) piridina (Pybox), permiten cicloadiciones altamente enantioselectivas de 1,3-dipolar de 2-benzopirilio-4-olatos.
Área de la Ciencia:
- Química orgánica es la química orgánica.
- Catalización asimétrica por catálisis asimétrica.
Sus antecedentes:
- Las reacciones de cicloadición 1,3-dipolar son cruciales para la síntesis de compuestos heterocíclicos.
- Lograr una alta enantioselectividad en estas reacciones es esencial para producir moléculas quirales.
Objetivo del estudio:
- Investigar el uso de complejos quirales de triflato de metales de tierras raras 2,6-bis (oxazolinilo) piridina (Pybox) como catalizadores de ácido de Lewis.
- Para lograr una enantioselectividad significativa en las cicloadiciones 1,3-dipolares de 2-benzopirilio-4-olatos.
Principales métodos:
- Utilizó complejos quirales Pybox-triflato de metales de tierras raras como catalizadores de ácido de Lewis.
- Realizó reacciones de cicloadición de 1,3-dipolar con varios sustratos, incluidos los derivados de benziloxiacetaldehído, piruvato de bencilo y 3-acriloil-2-oxazolidinona.
- Se emplean catalizadores basados en escandio (Sc(III)) e iterbio (Yb(III)) con diferentes ligandos Pybox (i-Pr y Ph).
Principales resultados:
- Las reacciones catalizadas por Sc(III) -Pybox-i-Pr produjeron endoaductos con hasta un 93% de exceso enantiomérico (ee).
- La reacción con el piruvato de bencilo proporcionó un exoaducto con 87% ee.
- Yb(III) - Pybox-Ph catalizó efectivamente la reacción con 3-acriloil-2-oxazolidinona, produciendo un exo-adducto con 98% ee.
Conclusiones:
- Los complejos de triflato de metales de tierras raras Pybox-chiral son catalizadores efectivos para las cicloadiciones 1,3-dipolares enantioselectivas.
- La elección del metal y el ligando Pybox influye en el resultado estereoquímico (endo/exo) y en la enantioselectividad de las reacciones.
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