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Videos de Conceptos Relacionados

Cycloaddition Reactions: Overview01:16

Cycloaddition 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.
Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation02:24

Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation

Introduction
Like alkenes, alkynes can be reduced to alkanes in the presence of transition metal catalysts such as Pt, Pd, or Ni. The reaction involves two sequential syn additions of hydrogen via a cis-alkene intermediate.
Cycloaddition Reactions: MO Requirements for Thermal Activation01:16

Cycloaddition Reactions: MO Requirements for Thermal Activation

Thermal cycloadditions are reactions where the source of activation energy needed to initiate the reaction is provided in the form of heat. A typical example of a thermally-allowed cycloaddition is the Diels–Alder reaction, which is a [4 + 2] cycloaddition. In contrast, a [2 + 2] cycloaddition is thermally forbidden.
Alkenes via Reductive Coupling of Aldehydes or Ketones: McMurry Reaction01:22

Alkenes via Reductive Coupling of Aldehydes or Ketones: McMurry Reaction

The radical dimerization of ketones or aldehydes gives vicinal diols through a pinacol coupling reaction. However, the behavior of titanium metals used for the reaction as a source of electrons is unusual. When the reaction is carried out in the presence of titanium, diols can be isolated at low temperatures. Else titanium further reacts with diols, forming alkenes through the McMurry reaction.
Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation02:47

Alkynes 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.
[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction01:16

[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction

The Diels–Alder reaction is an example of a thermal pericyclic reaction between a conjugated diene and an alkene or alkyne, commonly referred to as a dienophile. The reaction involves a concerted movement of six π electrons, four from the diene and two from the dienophile, forming an unsaturated six-membered ring. As a result, these reactions are classified as [4+2] cycloadditions.

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El enal-alquino intermolecular catalítico [3 + 2] es una reducción de cicloadiciones.

Ananda Herath1, John Montgomery

  • 1Department of Chemistry, University of Michigan, 930 North University Avenue, Ann Arbor, MI 48109-1055, USA.

Journal of the American Chemical Society
|October 26, 2006
PubMed
Resumen

Una nueva reacción de cicloadición catalizada por níquel combina moléculas acíclicas simples en anillos de cinco miembros. Este proceso reductor utiliza trietilborano y un disolvente prótico para una síntesis eficiente.

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Área de la Ciencia:

  • Química orgánica es la química orgánica.
  • La catálisis de la catálisis.
  • Metodología sintética de la metodología sintética.

Sus antecedentes:

  • Las reacciones de cicloadición son fundamentales en la síntesis orgánica para la construcción de moléculas cíclicas.
  • El desarrollo de métodos catalíticos para [3 + 2] cicloadiciones, especialmente aquellos que involucran precursores acíclicos simples, sigue siendo un área activa de investigación.
  • Las cicloadiciones reductivas ofrecen vías únicas para acceder a estructuras complejas a partir de materiales de partida fácilmente disponibles.

Objetivo del estudio:

  • Desarrollar una nueva reacción de cícloadición intermolecular [3 + 2] reductora y catalítica.
  • Establecer una estrategia catalizada por níquel para la síntesis de anillos de cinco miembros a partir de enalos y alquinas.
  • Investigar el papel del trietilborano como agente reductor y la influencia de los disolventes protóticos en esta transformación.

Principales métodos:

  • Empleando un catalizador de níquel para mediar la reacción de cicloadición entre enalos y alquinas.
  • Utilizando el trietilborano (Et3B) como agente reductor estequiométrico para lograr una reducción neta de dos electrones.
  • Llevar a cabo la reacción en un disolvente protótico, identificado como un parámetro clave para una transformación exitosa.

Principales resultados:

  • Desarrolló con éxito una cicloadición reductora catalítica, intermolecular [3 + 2] de enalos y alquinas.
  • Demostró una estrategia catalizada por níquel para combinar eficientemente dos sencillos sistemas pi acíclicos.
  • Se obtienen productos de anillo de cinco miembros a través de un proceso de reducción de dos electrones netos.
  • Destacó el papel crítico de los disolventes protóticos para facilitar la reacción.

Conclusiones:

  • El método desarrollado proporciona una ruta eficiente a los compuestos heterocíclicos de cinco miembros.
  • Esta cicloadición reductora catalizada por níquel ofrece una herramienta valiosa para la síntesis orgánica.
  • La dependencia de la reacción en materiales de partida simples y condiciones suaves hace que sea sintéticamente útil.