Video Experimental Relacionado
Updated: Jun 11, 2026
10:17
Efficient Construction of Drug-like Bispirocyclic Scaffolds Via Organocatalytic Cycloadditions of α-Imino γ-Lactones and Alkylidene Pyrazolones
Published on: February 7, 2019
Control electrónico y estérico de las regioselectividades en las cicloadiciones catalizadas por Rh (I) (5 + 2):
Peng Liu1, Lauren E Sirois, Paul Ha-Yeon Cheong
1Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569, USA.
Journal of the American Chemical Society
|July 1, 2010
Resumen
Las cicloadiciones catalizadas por Rh (I) (5 + 2) entre los vinilciclopropanos (VCP) y las alquinas muestran una regioselectividad predecible basada en la posición del sustituyente. Los efectos estéricos y electrónicos en el estado de transición gobiernan el resultado de estas importantes reacciones orgánicas.
Área de la Ciencia:
- Química orgánica es la química orgánica.
- La catálisis de la catálisis.
- Mecanismo de reacción Mecanismo de reacción
Sus antecedentes:
- Los vinilciclopropanos (VCP) son versátiles bloques de construcción en la síntesis orgánica.
- Las cicloadiciones catalizadas por el rodio ((I) (5 + 2) ofrecen una ruta poderosa a estructuras cíclicas complejas.
- La regioselectividad en estas reacciones, particularmente con las alquinas asimétricas, sigue siendo un área que requiere una investigación detallada.
Objetivo del estudio:
- Investigar la regioselectividad de las cicloadiciones (5 + 2) catalizadas por Rh (I) entre VCPs y alquinas no simétricas.
- Establecer un modelo predictivo para controlar el resultado regioquímico.
- Comprender la influencia de los efectos de los sustituyentes en la selectividad de la reacción.
Principales métodos:
- Estudios experimentales que involucran varios VCPs y alquinas sustituidos.
- Cálculos de la Teoría Funcional de Densidad (DFT) para el análisis mecanicista.
- Análisis de los productos de reacción para determinar los ratios de regioselectividad.
Principales resultados:
- Se observó una alta regioselectividad (>20:1) para los VCP con sustitución terminal de alquenos, consistente con los modelos estéricos.
- Se encontró una regioselectividad variable (variando de >20:1 a 1:2.3) para los PCV con sustitución interna de alquenos.
- Se propuso un modelo refinado que incorporaba los efectos electrónicos de los sustituyentes de alquinos para explicar las tendencias observadas.
Conclusiones:
- La regioselectividad de las cicloadiciones catalizadas por Rh (I) (5 + 2) está influenciada por factores estéricos y electrónicos.
- La sustitución VCP terminal conduce a una regioselectividad predecible impulsada por estéricos.
- La sustitución interna de VCP y los grupos alquinos que retiran electrones pueden alterar la selectividad a través de la estabilización del estado de transición.
Más Videos Relacionados
![Solid-phase Synthesis of [4.4] Spirocyclic Oximes](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2FCDNSource%2Fteasers%2F58508.jpg&w=3840&q=50)
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.
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.
02:17Regioselectivity of Electrophilic Additions to Alkenes: Markovnikov's Rule
If a set of reactants can yield multiple constitutional isomers, but one of the isomers is obtained as the major product, the reaction is said to be regioselective. In such reactions, bond formation or breaking is favored at one reaction site over others.
The hydrohalogenation of an unsymmetrical alkene can yield two haloalkane products, depending on which vinylic carbon takes up the halogen. However, one product usually predominates, where hydrogen adds to the vinylic carbon bearing the...
The hydrohalogenation of an unsymmetrical alkene can yield two haloalkane products, depending on which vinylic carbon takes up the halogen. However, one product usually predominates, where hydrogen adds to the vinylic carbon bearing the...
01:16Cycloaddition Reactions: Overview
Cycloadditions are one of the most valuable and effective synthesis routes to form cyclic compounds. These are concerted pericyclic reactions between two unsaturated compounds resulting in a cyclic product with two new σ bonds formed at the expense of π bonds. The [4 + 2] cycloaddition, known as the Diels–Alder reaction, is the most common. The other example is a [2 + 2] cycloaddition.
01:34Woodward–Hoffmann Selection Rules and Microscopic Reversibility
Electrocyclic reactions, cycloadditions, and sigmatropic rearrangements are concerted pericyclic reactions that proceed via a cyclic transition state. These reactions are stereospecific and regioselective. The stereochemistry of the products depends on the symmetry characteristics of the interacting orbitals and the reaction conditions. Accordingly, pericyclic reactions are classified as either symmetry-allowed or symmetry-forbidden. Woodward and Hoffmann presented the selection criteria for...
01:23Electrophilic Addition of HX to 1,3-Butadiene: Thermodynamic vs Kinetic Control
The addition of a hydrogen halide to 1,3-butadiene gives a mixture of 1,2- and 1,4-adducts. Since more substituted alkenes are more stable, the 1,4-adduct is expected to be the major product. However, the product distribution is strongly influenced by temperature; low temperature favors the 1,2-adduct, whereas the 1,4-adduct is predominant at high temperature.