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Estudios mecanicistas sobre la borilación de arseno electrófilo mediada por aminas y su aplicación en la síntesis de
Viktor Bagutski1, Alessandro Del Grosso, Josue Ayuso Carrillo
1Department of Chemistry, University of Manchester, Manchester, M13 9PL, United Kingdom.
Journal of the American Chemical Society
|December 5, 2012
Resumen
La borilación electrofílica directa de arenas y heteroarenos se consigue utilizando Y(2)BCl y AlCl(3) con aminas. Este método produce boronatos MIDA estables y procede a través de mecanismos S(E) Ar con cationes de borenio para sustratos activados.
Área de la Ciencia:
- Química orgánica es la química orgánica.
- Química organometálica Química orgánica de los metales.
- Metodología sintética de la metodología sintética.
Sus antecedentes:
- La borilación electrófila es una transformación crucial para la síntesis de compuestos de organoboron.
- El desarrollo de métodos eficientes y versátiles para la borilación directa sigue siendo un área activa de investigación.
Objetivo del estudio:
- Desarrollar un método de borilación electrofílica directa para una amplia gama de arenas y heteroarenas.
- Para investigar los mecanismos de reacción e identificar los intermediarios clave.
- Para permitir la síntesis de boronatos MIDA estables.
Principales métodos:
- Borilación electrofílica directa utilizando Y(2) BCl (Y(2) = Cl(2) o o-catecolato) con AlCl(3) equimolar y una amina terciaria.
- Funcionalización in situ de los productos ArBCl{2) con TMS{2) MIDA.
- Combinación de estudios experimentales y computacionales para elucidar los mecanismos de reacción.
Principales resultados:
- Borilación exitosa de diversas arenas y heteroarenos en rendimientos de moderados a buenos.
- Formación de boronatos MIDA estables en el banco.
- Identificación de los cationes de borenio, [Y(2) B(amina) ](+), como electrófilos clave en el mecanismo S(E) Ar para los arenos activados.
- Elucidación de dos vías dependientes de aminas para las catecolatoborocaciones.
- Mecanismos alternativos identificados para arenas pobremente activadas y reacciones con aminas voluminosas.
Conclusiones:
- Se ha establecido un versátil protocolo de borilación electrofílica directa.
- El estudio proporciona información mecanicista sobre la borilación de varios sustratos aromáticos.
- El método desarrollado ofrece una ruta práctica a los valiosos bloques de construcción de boronato MIDA.
Videos de Conceptos Relacionados
03:08Hydroboration-Oxidation of Alkenes
In addition to the oxymercuration–demercuration method, which converts the alkenes to alcohols with Markovnikov orientation, a complementary hydroboration-oxidation method yields the anti-Markovnikov product. The hydroboration reaction, discovered in 1959 by H.C. Brown, involves the addition of a B–H bond of borane to an alkene giving an organoborane intermediate. The oxidation of this intermediate with basic hydrogen peroxide forms an alcohol.
01:38Preparation of Amines: Reductive Amination of Aldehydes and Ketones
Carbonyl compounds and primary amines undergo reductive amination first to produce imines, followed by secondary amines in the same reaction mixture, using selective reducing agents like sodium cyanoborohydride or sodium triacetoxyborohydride. Reductive amination produces different degrees of substitution of amines depending on the starting amine substrate.
02:47Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation
Introduction
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
02:36Regioselectivity and Stereochemistry of Hydroboration
A significant aspect of hydroboration–oxidation is the regio- and stereochemical outcome of the reaction.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.
01:19Amines to Amides: Acylation of Amines
Various carboxylic acid derivatives (such as acid chlorides, esters, and anhydrides) can be used for the acylation of amines to yield amides. The reaction requires two equivalents of amines. The first amine molecule functions as a nucleophile and attacks the carbonyl carbon to produce a tetrahedral intermediate. This is followed by the loss of the leaving group and restoration of the C=O bond.
Next, the second equivalent of amine serves as a Brønsted base and deprotonates the quaternary amide...
Next, the second equivalent of amine serves as a Brønsted base and deprotonates the quaternary amide...
01:20Electrophilic Aromatic Substitution: Nitration of Benzene
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