Mechanism of the Stereoselective α‐Alkylation of Aldehydes Driven by the Photochemical Activity of Enamines
Herein we describe our efforts to elucidate the key mechanistic aspects of the previously reported enantiose- lective photochemical α-alkylation of aldehydes with electron- poor organic halides. The chemistry exploits the potential of chiral enamines, key organocatalytic intermediates in thermal asy...
| Autores: | , |
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| Tipo de recurso: | artículo |
| Estado: | Versión aceptada para publicación |
| Fecha de publicación: | 2016 |
| País: | España |
| Institución: | Varias* (Consorci de Biblioteques Universitáries de Catalunya, Centre de Serveis Científics i Acadèmics de Catalunya) |
| Repositorio: | Recercat. Dipósit de la Recerca de Catalunya |
| OAI Identifier: | oai:recercat.cat:2072/350687 |
| Acceso en línea: | http://hdl.handle.net/2072/350687 https://doi.org/10.1021/jacs.6b04871 |
| Access Level: | acceso abierto |
| Palabra clave: | 54 |
| Sumario: | Herein we describe our efforts to elucidate the key mechanistic aspects of the previously reported enantiose- lective photochemical α-alkylation of aldehydes with electron- poor organic halides. The chemistry exploits the potential of chiral enamines, key organocatalytic intermediates in thermal asymmetric processes, to directly participate in the photo- excitation of substrates either by forming a photoactive electron donor−acceptor complex or by directly reaching an electronically excited state upon light absorption. These photochemical mechanisms generate radicals from closed- shell precursors under mild conditions. At the same time, the ground-state chiral enamines provide effective stereochemical control over the enantioselective radical-trapping process. We use a combination of conventional photophysical investigations, nuclear magnetic resonance spectroscopy, and kinetic studies to gain a better understanding of the factors governing these enantioselective photochemical catalytic processes. Measurements of the quantum yield reveal that a radical chain mechanism is operative, while reaction-profile analysis and rate-order assessment indicate the trapping of the carbon-centered radical by the enamine, to form the carbon−carbon bond, as rate-determining. Our kinetic studies unveil the existence of a delicate interplay between the light-triggered initiation step and the radical chain propagation manifold, both mediated by the chiral enamines. |
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