Síntesis asimétrica catalítica de ésteres aleloicos quirales
Stefan F Kirsch1, Larry E Overman
1Department of Chemistry, 516 Rowland Hall, University of California, Irvine, California 92697-2025, USA.
Journal of the American Chemical Society
|March 3, 2005
Resumen
Los 3-aciloxi-1-alquenos quirales se sintetizan a partir de alcenoles proquirales utilizando un nuevo catalizador de paladio. Esta eficiente reacción enantioselectiva ocurre a temperatura ambiente con un alto estereocontrol.
Área de la Ciencia:
- Química orgánica es la química orgánica.
- Síntesis asimétrica de síntesis.
- Química organometálica Química orgánica de los metales.
Sus antecedentes:
- El prociral (Z)-2-alceno-1-ol es un valioso intermediario sintético.
- El desarrollo de métodos catalíticos eficientes para las transformaciones enantioselectivas es crucial en la síntesis orgánica.
Objetivo del estudio:
- Desarrollar un nuevo sistema catalítico para la síntesis enantioselectiva de 3-aciloxi-1-alquenos quirales.
- Investigar el alcance y el mecanismo de esta nueva transformación.
Principales métodos:
- Reacción de los derivados del tricloroacetimidato de los prochiral (Z)-2-alquen-1-ols con los ácidos carboxílicos.
- Utilizando un catalizador quiral de paladio, se obtiene di-mu-acetatobis[(eta5-(S) -(pR)-2-(2'-(4'-metiletilo) oxazolinilo) ciclopentadienilo,1-C,3'-N) ((eta4-tetrafenilciclobutadieno) cobalto] dipalladio (COP-OAc) o su enantiómero.
Principales resultados:
- Se logró una alta enantiopuridad de los 3-aciloxi-1-alquenos quirales.
- La reacción demostró un amplio alcance de sustrato y una alta estereoinducción predecible.
- El proceso es eficiente, funcionando a temperatura ambiente con altas concentraciones de sustrato y bajas cargas de catalizador.
Conclusiones:
- Se ha establecido un método nuevo y eficiente para la síntesis enantioselectiva de 3-aciloxi-1-alquenos quirales.
- Es probable que la reacción proceda a través de un nuevo mecanismo catalítico, lo que justifica una mayor investigación.
Videos de Conceptos Relacionados
01:12Acid Halides to Esters: Alcoholysis
Alcoholysis is a nucleophilic acyl substitution reaction in which an alcohol functions as a nucleophile. Acid halides react with alcohol to produce esters. The mechanism proceeds in three steps:
01:13Esters to Carboxylic Acids: Acid-Catalyzed Hydrolysis
Hydrolysis of esters under acidic conditions proceeds through a nucleophilic acyl substitution. In the presence of excess water, the reaction proceeds in a reversible manner, forming carboxylic acids and alcohols.
During hydrolysis, the ester is first activated towards nucleophilic attack through the protonation of the carboxyl oxygen atom by the acid catalyst. The protonation makes the ester carbonyl carbon more electrophilic. In the next step, water acts as a nucleophile and adds to the...
During hydrolysis, the ester is first activated towards nucleophilic attack through the protonation of the carboxyl oxygen atom by the acid catalyst. The protonation makes the ester carbonyl carbon more electrophilic. In the next step, water acts as a nucleophile and adds to the...
01:24Esters to β-Ketoesters: Claisen Condensation Overview
Regular Claisen condensation is a base-promoted reaction involving identical esters with two α hydrogens, condensing to produce β-ketoesters. It is a nucleophilic acyl substitution reaction wherein one of the ester molecules, upon deprotonation by the base, forms a nucleophilic enolate ion, while the other molecule serves as an electrophile.
01:18β-Dicarbonyl Compounds via Crossed Claisen Condensations
Crossed Claisen condensations are base-promoted reactions between two different ester molecules producing β-dicarbonyl compounds. The reaction involving esters, with both containing α hydrogen, results in a mixture of four different products that are difficult to isolate. This reduces the synthetic utility of the reaction.
01:08Esters to β-Ketoesters: Claisen Condensation Mechanism
Regular Claisen condensation involves the synthesis of β-ketoesters by combining identical ester molecules bearing two α hydrogens in the presence of an alkoxide base. The reaction commences with the deprotonation of the acidic α hydrogen by the base to form a resonance stabilized ester enolate. This nucleophilic ion then attacks the carbonyl center of another ester molecule to generate a tetrahedral alkoxide intermediate. Next, the expulsion of the alkoxide group from the intermediate restores...
01:13Carboxylic Acids to Esters: Acid-Catalyzed (Fischer) Esterification Mechanism
Carboxylic acids react with alcohols to yield esters via an acid-catalyzed condensation reaction called Fischer esterification. This is a nucleophilic acyl substitution reaction that proceeds via a tetrahedral intermediate, where a water molecule is eliminated as the leaving group.