Video Experimental Relacionado
Updated: Jun 28, 2026
09:58
Metal-free Synthesis of Ynones from Acyl Chlorides and Potassium Alkynyltrifluoroborate Salts
Published on: February 24, 2015
Reactividad ortogonal en los organotrifluoroboratos sustituidos por borilo
Gary A Molander1, Deidre L Sandrock
1Roy and Diana Vagelos Laboratories, Department of Chemistry, University of Pennsylvania, 231 South 34th Street, Philadelphia, Pennsylvania 19104-6323, USA. gmolandr@sas.upenn.edu
Journal of the American Chemical Society
|November 5, 2008
Resumen
Un nuevo método de hidroboración crea intermedios de dibora a partir de los organotrifluoroboratos. Esto permite el acoplamiento cruzado selectivo, preservando el trifluoroborato para reacciones posteriores, simplificando la síntesis de moléculas complejas.
Área de la Ciencia:
- Química orgánica es la química orgánica.
- Química del organoborón Química del organoborón
Sus antecedentes:
- Los organotrifluoroboratos ofrecen una reactividad única en la síntesis orgánica.
- El desarrollo de métodos eficientes para la funcionalización de compuestos de organoboron es crucial para la construcción de moléculas complejas.
Objetivo del estudio:
- Desarrollar un nuevo método de hidroboración para organotrifluoroboratos que contienen alquenilo.
- Para permitir reacciones de acoplamiento cruzado quimioselectivo utilizando los intermediarios de dibora generados.
- Establecer una secuencia de una sola olla para una síntesis eficiente de productos elaborados.
Principales métodos:
- Hidroboración de organotrifluoroboratos que contienen alkenilo para formar intermedios de dibora.
- Acoplamiento cruzado quimioselectivo de la fracción de borano con haluros de arilo.
- Secuencia de acoplamiento cruzado bidireccional / hidroboración de una olla.
- Aplicación de condiciones a los trialquilboranos y a los organotrifluoroboratos que contienen halo.
Principales resultados:
- Generación exitosa de productos intermedios de dibora a través de la hidroboración.
- Alta quimioselectividad en el acoplamiento cruzado, preservando el grupo trifluoroborato.
- Demostración de una secuencia de un solo vaso que produce moléculas complejas en buenos rendimientos.
- Amplia aplicabilidad a diferentes sustratos de organoboron.
Conclusiones:
- El método desarrollado proporciona una estrategia versátil para la funcionalización del organoboron.
- La estabilidad de la fracción de trifluoroborato es clave para las transformaciones secuenciales.
- Este enfoque facilita la construcción eficiente y simple de arquitecturas moleculares complejas.
Videos de Conceptos Relacionados
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.
01:11ortho–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...
01:13Electrophilic Aromatic Substitution: Fluorination and Iodination of Benzene
Bromination and chlorination of aromatic rings by electrophilic aromatic substitution reactions are easily achieved, but fluorination and iodination are difficult to achieve. Fluorine is so reactive that its reaction with benzene is difficult to control, resulting in poor yields of monofluoroaromatic products. To address this, Selectfluor reagent is used as a fluorine source in which a fluorine atom is bonded to a positively charged nitrogen.
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.
01:24ortho–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...
02:35Regioselectivity of Electrophilic Additions-Peroxide Effect
In the presence of organic peroxides, the addition of hydrogen bromide to an alkene yields the isomer that is not predicted by Markovnikov’s rule. For example, the addition of hydrogen bromide to 2-methylpropene in the presence of peroxides gives 1-bromo-2-methylpropane. This addition reaction proceeds via a free radical mechanism, which reverses the regioselectivity. The free radical reaction mechanism involves three stages: initiation, propagation, and termination.