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Ciclorreversión paso a paso de cationes radicales de oxetano con escisión inicial de enlace C-O
Miguel A Miranda1, M Angeles Izquierdo
1Departamento de Química/Instituto de Tecnología Química UPV- CSIC, Universidad Politécnica de Valencia, Camino Vera s/n, Apdo. 22012, 46022, Valencia, Spain. mmiranda@qim.upv.es
Journal of the American Chemical Society
|June 6, 2002
Resumen
Las sales de 2,4,6-Triaryl ((thia) pirílio facilitan la ciclo-reversión del oxetano. El catión radical del 2,3-difenil-4-hidroximetiloxetano se somete a una escisión O-C2, formando un producto tetrahidrofurano en un lapso de submicrosegundos.
Área de la Ciencia:
- La fotoquímica es la fotoquímica.
- Química orgánica es la química orgánica.
- Mecanismos de reacción Mecanismos de reacción
Sus antecedentes:
- Las sales de 2,4,6-Triaryl ((thia) pirílio son fotosensibilizantes de transferencia de electrones.
- Los sistemas de anillos de oxetano son susceptibles a la ciclo-reversión inducida fotoquímicamente.
- La comprensión de las vías de fragmentación de los oxetanos sustituidos es crucial para las aplicaciones sintéticas.
Objetivo del estudio:
- Para investigar el mecanismo de ciclo-reversión del 2,3-difenil-4-hidroximetiloxetano utilizando fotosensibilización.
- Para dilucidar las especies intermedias y vías de fragmentación involucradas en la reacción fotoquímica.
- Para determinar la cinética de la formación de productos y las rutas de fragmentación competitivas.
Principales métodos:
- Se utilizan sales de 2,4,6-Triaryl ((thia) pirílio como fotosensibilizantes.
- Estudió la fotoquímica del 2,3-difenil-4-hidroximetiloxetano (1).
- Se empleó espectroscopia de resolución temporal para monitorear los intermediarios de reacción y la cinética.
Principales resultados:
- El catión radical de oxetano (1) se somete a una escisión gradual, comenzando con la escisión del enlace O-C2.
- Un intermedio transitorio localiza el giro en el oxígeno y la carga en el carbono.
- El ataque nucleófilo intramolecular conduce a la formación de 2,3-difenil-4-hidroxitetrahidrofurano (4a) en una escala de tiempo submicrosegundo.
- La escisión competitiva C3-C4 forma el catión radical transestilbeno (λmax = 470 nm).
Conclusiones:
- La vía fotoquímica primaria para el oxetano (1) implica la escisión secuencial O-C2 y la ciclización intramolecular.
- La cinética observada indica una rápida formación del producto tetrahidrofurano.
- El estudio proporciona una visión mecanicista detallada de la ciclo-reversión del oxetano fotosensibilizado con oxetano.
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