Video Experimental Relacionado
Updated: May 31, 2026
09:45
A Protocol for Safe Lithiation Reactions Using Organolithium Reagents
Published on: November 12, 2016
Sobre la naturaleza del heteroacoplamiento oxidativo de los enolados de litio
Brian M Casey1, Robert A Flowers
1Department of Chemistry, Lehigh University, Bethlehem, Pennsylvania 18015, USA.
Journal of the American Chemical Society
|July 5, 2011
Resumen
La formación selectiva de 1,4-dicarbonilos a través del acoplamiento enolado se logra a través de la heteroagregación. Este estudio revela que la heteroagregación de enolato de litio impulsa el heteroacoplamiento selectivo, produciendo más de las cantidades estadísticamente predichas.
Área de la Ciencia:
- Química orgánica es la química orgánica.
- Química sintética de la química sintética.
Sus antecedentes:
- La oxidación de un solo electrón de los enolados ofrece una vía directa a los compuestos 1,4-dicarbonilo.
- El heteroacoplamiento intermolecular de distintos enolados a través de la oxidación de un solo electrón puede producir productos sintéticamente valiosos en altos rendimientos.
Objetivo del estudio:
- Aclarar el mecanismo detrás de la formación selectiva de productos heteroacoplados en reacciones de acoplamiento de enolados.
- Comprender los factores que contribuyen a que los rendimientos superen las predicciones estadísticas en las reacciones de heteroacoplamiento.
Principales métodos:
- Se emplearon estudios cinéticos para analizar las velocidades y vías de reacción.
- (7) La espectroscopia de resonancia magnética nuclear (RMN) de litio se utilizó para investigar el estado de agregación de los enolados de litio.
- Se llevaron a cabo estudios sintéticos para confirmar la formación y el rendimiento del producto.
Principales resultados:
- Los datos experimentales indican que la formación selectiva de productos heteroacoplados no es aleatoria.
- La evidencia apunta hacia la asociación preferencial de diferentes enolados de litio (heteroagregación) como el factor clave.
- Esta heteroagregación influye en el resultado de la reacción, lo que lleva a mayores rendimientos de los productos heteroacoplados deseados.
Conclusiones:
- La síntesis selectiva de 1,4-dicarbonilos a través del heteroacoplamiento de enolato intermolecular se rige por la heteroagregación de enolato de litio.
- Comprender y controlar la heteroagregación es crucial para optimizar las estrategias sintéticas en la química de los enolados.
- Este hallazgo proporciona información fundamental sobre la formación selectiva de enlaces C-C a través de intermediarios radicales.
Videos de Conceptos Relacionados
01:23Reactivity of Enolate Ions
Enolate ions are formed by the acid–base reaction of a carbonyl compound with a base. This leads to deprotonation of the α hydrogen atom, leading to a resonance-stabilized enolate ion where one of the contributing structures is an oxyanion, which imparts additional stability. Therefore, the proton on the α carbon is more acidic in nature than that of other sp3-hybridized C–H bonds but less acidic than those in O–H bonds where the negative charge in the conjugate base is localized on the oxygen...
01:10α-Alkylation of Ketones via Enolate Ions
Ketones with α protons are deprotonated by strong bases like lithium diisopropylamide (LDA) to form enolate ions. The anion is stabilized by resonance, and its hybrid structure exhibits negative charges on the carbonyl oxygen and the α carbon. This ambident nucleophile can attack an electrophile via two possible sites: the carbonyl oxygen, known as O-attack, or the α carbon, known as C-attack. The nucleophilic attack via the carbanionic site is preferred. This is due to the strong interaction...
01:33Regioselective Formation of Enolates
As depicted in the figure below, the unsymmetrical ketones can form two possible enolates: less substituted or more substituted enolates. Usually, the thermodynamic enolates are formed from the more substituted α-carbon atom, while the kinetic enolates are formed faster by deprotonation from the less substituted position. The thermodynamic enolates have lower energy, so they are more stable. But the energy required to form kinetic enolates is less.
01:12Stereochemical Effects of Enolization
The chiral α-carbon of the carbonyl compound is the stereocenter of the molecule. As shown in the figure below, when such a carbonyl compound undergoes racemization under an acidic or basic condition, an achiral enol is formed.
01:15Enolate Mechanism Conventions
When a carbonyl compound is treated with a strong base, the α position gets deprotonated to give a resonance-stabilized intermediate called an enolate. Enolates are ambident nucleophiles because they possess two nucleophilic sites that can attack an electrophile owing to the delocalization of the negative charge between the α carbon and oxygen atoms. When the oxygen atom attacks an electrophile, it is called O-attack, whereas electrophilic attack via the α carbon is known as C-attack.
C-attack...
C-attack...
01:18Reactivity of Enols
Enols are a class of compounds where a hydroxyl group is attached to a carbon–carbon double bond, which implies that it is a vinyl alcohol. A carbonyl compound with an α hydrogen undergoes keto–enol tautomerism and remains in equilibrium with its tautomer, the enol form. Usually, the keto tautomer is present in a higher concentration than the enol tautomer due to the higher bond energy of C=O compared to C=C. Moreover, the direction of the keto–enol equilibrium is governed by factors like...