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Videos de Conceptos Relacionados

Thermal Electrocyclic Reactions: Stereochemistry01:17

Thermal Electrocyclic Reactions: Stereochemistry

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The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
2.1K
Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

2.4K
Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
2.4K
[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction01:16

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

10.3K
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.
10.3K
Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

1.9K
The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
1.9K
Reduction of Alkenes: Asymmetric Catalytic Hydrogenation02:17

Reduction of Alkenes: Asymmetric Catalytic Hydrogenation

3.4K
Catalytic hydrogenation of alkenes is a transition-metal catalyzed reduction of the double bond using molecular hydrogen to give alkanes. The mode of hydrogen addition follows syn stereochemistry.
The metal catalyst used can be either heterogeneous or homogeneous. When hydrogenation of an alkene generates a chiral center, a pair of enantiomeric products is expected to form. However, an enantiomeric excess of one of the products can be facilitated using an enantioselective reaction or an...
3.4K
Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation02:24

Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation

7.9K
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.
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Accessing Valuable Ligand Supports for Transition Metals: A Modified, Intermediate Scale Preparation of 1,2,3,4,5-Pentamethylcyclopentadiene
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Accessing Valuable Ligand Supports for Transition Metals: A Modified, Intermediate Scale Preparation of 1,2,3,4,5-Pentamethylcyclopentadiene

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Deshidrogenación mecanoquímica mediada por litio

Kanna Fujishiro1, Yuta Morinaka2, Yohei Ono2

  • 1Department of Chemistry, Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan.

Journal of the American Chemical Society
|April 3, 2023
PubMed
Resumen
Este resumen es generado por máquina.

Los investigadores desarrollaron una nueva ciclodehidrogenación aniónica mecanoquímica mediada por litio 0. Este método fácil de usar sintetiza eficientemente hidrocarburos aromáticos policíclicos y nanografenos, incluido el rileno molecular no sustituido más largo, el quinterrileno.

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Área de la Ciencia:

  • Síntesis orgánica
  • Química de los materiales
  • Nanotecnología

Sus antecedentes:

  • La ciclodehidrogenación es crucial para la síntesis de hidrocarburos aromáticos policíclicos (HAP), compuestos heteroaromáticos y nanografenos.
  • La ciclodehidrogenación aniónica utilizando potasio es efectiva para crear estructuras de rilenos, pero sufre de poca practicidad, piroforicidad y escalabilidad.
  • Los métodos existentes presentan desafíos significativos para una aplicación sintética generalizada.

Objetivo del estudio:

  • Desarrollar un método nuevo, práctico y escalable para la ciclodehidrogenación aniónica.
  • Establecer un protocolo fácil de usar para la síntesis de HAP y nanografenos.
  • Para sintetizar nuevos nanographenes, incluido el rileno molecular no sustituido más largo.

Principales métodos:

  • Desarrollo de una reacción de ciclodehidrogenación aniónica mecanoquímica mediada por litio.
  • Utilizando el alambre de litio convencional a temperatura ambiente y bajo aire.
  • Investigar el alcance de la reacción, el mecanismo y la síntesis a escala de gramos a través de análisis computacionales y RMN.

Principales resultados:

  • Se obtiene una síntesis eficiente de perileno a partir de 1,1'-binaftil en 30 minutos con un rendimiento del 94%.
  • Demostró la practicidad de la reacción, la tolerancia al aire y el funcionamiento a temperatura ambiente.
  • Sintetizó con éxito nuevos nanografenos a través de múltiples ciclodehidrogenaciones, incluido el quinterrileno ([5]rileno).

Conclusiones:

  • El protocolo mecanoquímico mediado por litio ofrece ventajas significativas en cuanto a practicidad y aplicabilidad con respecto a los métodos existentes.
  • Este enfoque fácil de usar permite la síntesis de nanografenos complejos, expandiendo las capacidades sintéticas.
  • El estudio proporciona una comprensión completa del alcance, el mecanismo y las limitaciones de la reacción, allanando el camino para futuras aplicaciones.