Video Experimental Relacionado
Updated: Jul 6, 2026
06:34
Synthesis of Antiviral Tetrahydrocarbazole Derivatives by Photochemical and Acid-catalyzed C-H Functionalization via Intermediate Peroxides (CHIPS)
Published on: June 20, 2014
Ciclización altamente eficiente y enantioselectiva de iminas aromáticas a través de la activación dirigida del enlace
Reema K Thalji1, Jonathan A Ellman, Robert G Bergman
1Center for New Directions in Organic Synthesis, Department of Chemistry, University of California-Berkeley, Berkeley, California 94720, USA.
Journal of the American Chemical Society
|June 10, 2004
Resumen
Este estudio introduce la primera reacción catalítica altamente enantioselectiva para la activación de enlaces aromáticos C-H. Este avance permite una ciclización eficiente y selectiva de las ketiminas aromáticas en condiciones más suaves.
Área de la Ciencia:
- Química orgánica es la química orgánica.
- La catálisis es la catálisis.
- Síntesis asimétrica de síntesis.
Sus antecedentes:
- La activación del enlace aromático C-H es una transformación crucial en la síntesis orgánica.
- El desarrollo de métodos enantioselectivos para la activación de C-H sigue siendo un desafío importante.
- Los métodos anteriores para la alquilación intramolecular requerían temperaturas más altas.
Objetivo del estudio:
- Informar sobre la primera reacción catalítica altamente enantioselectiva que involucra la activación de enlaces aromáticos C-H.
- Desarrollar un sistema catalítico eficiente para la ciclización enantioselectiva de las ketiminas aromáticas meta-atadas.
- Para lograr condiciones de reacción más suaves en comparación con los sistemas achirales existentes.
Principales métodos:
- Se utilizó un catalizador de rodio, específicamente 5 mol % [RhCl(coe) ]2.2.
- Se empleó 15 mol % de un ligando de fosforamidita derivado de (S) -binol para la enantioselectividad.
- Investigó la ciclización enantioselectiva de las ketiminas aromáticas con grupos alquenilo.
Principales resultados:
- Se obtienen altas enantioselectividades, con hasta un 96% ee.
- Se obtiene hasta rendimientos cuantitativos para la reacción de ciclización.
- Demostró una reducción significativa en la temperatura de reacción (hasta 75 grados C más baja) en comparación con los sistemas achirales.
Conclusiones:
- El sistema catalítico desarrollado representa un avance significativo en la activación C-H aromática enantioselectiva.
- La reacción procede eficientemente en condiciones suaves, incluso a temperatura ambiente para ciertos sustratos.
- Esta metodología ofrece una poderosa herramienta para la síntesis asimétrica de moléculas orgánicas complejas.
Más Videos Relacionados
Videos de Conceptos Relacionados
01:21Acid-Catalyzed α-Halogenation of Aldehydes and Ketones
By replacing an α-hydrogen with a halogen, acid-catalyzed α-halogenation of aldehydes or ketones yields a monohalogenated product
In the first step of the mechanism, the acid protonates the carbonyl oxygen resulting in a resonance-stabilized cation, which subsequently loses an α-hydrogen to form an enol tautomer. The C=C bond in an enol is highly nucleophilic because of the electron-donating nature of the –OH group. Consequently, the double bond attacks an electrophilic halogen to form a...
In the first step of the mechanism, the acid protonates the carbonyl oxygen resulting in a resonance-stabilized cation, which subsequently loses an α-hydrogen to form an enol tautomer. The C=C bond in an enol is highly nucleophilic because of the electron-donating nature of the –OH group. Consequently, the double bond attacks an electrophilic halogen to form a...
01:26Photochemical Electrocyclic Reactions: Stereochemistry
The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
Selection Rules: Photochemical Activation
01:11ortho–para-Directing Activators: –CH3, –OH, –NH2, –OCH3
All ortho–para directors, excluding halogens, are activating groups. These groups donate electrons to the ring, making the ring carbons electron-rich. Consequently, the reactivity of the aromatic ring towards electrophilic substitution increases. For instance, the nitration of anisole is about 10,000 times faster than the nitration of benzene. The electron-donating effect of the methoxy group in anisole activates the ortho and para positions on the ring and stabilizes the corresponding...
01:24ortho–para-Directing Deactivators: Halogens
Halogens are ortho–para directors. They are more electronegative than carbon. Therefore, as ring substituents, they can withdraw electrons through the inductive effect and deactivate the aromatic ring towards electrophilic substitution. Halogens also have an electron-donating resonance effect on the ring, which influences the orientation of the incoming electrophile. If an electrophile attacks at the ortho or the para position, the halogen donates electrons and stabilizes the intermediate...
01:13meta-Directing Deactivators: –NO2, –CN, –CHO, –CO2R, –COR, –CO2H
All meta-directing substituents are deactivating groups. These substituents withdraw electrons from the aromatic ring, making the ring less reactive toward electrophilic substitution. For example, the nitration of nitrobenzene is 100,000 times slower than that of benzene because of the deactivating effect of the nitro group. The first step in an electrophilic aromatic substitution is the addition of an electrophile to form a resonance-stabilized carbocation. The energy diagrams for the...
01:12Double Resonance Techniques: Overview
Double resonance techniques in Nuclear Magnetic Resonance (NMR) spectroscopy involve the simultaneous application of two different frequencies or radiofrequency pulses to manipulate and observe two distinct nuclear spins. One important application of double resonance is spin decoupling, which selectively suppresses coupling with one type of nucleus while observing the NMR signal from another nucleus, simplifying the spectrum and enhancing resolution.
Spin decoupling is usually achieved by...
Spin decoupling is usually achieved by...