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Preparation of Alkynes: Alkylation Reaction02:27

Preparation of Alkynes: Alkylation Reaction

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Introduction
Alkylation of terminal alkynes with primary alkyl halides in the presence of a strong base like sodium amide is one of the common methods for the synthesis of longer carbon-chain alkynes. For example, treatment of 1-propyne with sodium amide followed by reaction with ethyl bromide yields 2-pentyne.
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ortho–para-Directing Activators: –CH3, –OH, –⁠NH2, –OCH301:11

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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...
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α-Alkylation of Ketones via Enolate Ions01:10

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Ketones with α protons are deprotonated by strong bases like lithium diisopropylamide (LDA) to form enolate ions. The anion is stabilized by resonance, and its hybrid structure exhibits negative charges on the carbonyl oxygen and the α carbon. This ambident nucleophile can attack an electrophile via two possible sites: the carbonyl oxygen, known as O-attack, or the α carbon, known as C-attack. The nucleophilic attack via the carbanionic site is preferred. This is due to the...
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Preparation of Amines: Alkylation of Ammonia and Amines01:30

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Alkylation is one of the methods used to prepare amines. Direct alkylation of ammonia or a primary amine with an alkyl halide gives polyalkylated amines along with a quaternary ammonium salt through successive SN2 reactions. This process of making the quaternary salt through the direct alkylation method is called exhaustive alkylation.
Each alkylation step makes the nitrogen center more nucleophilic, which triggers successive alkylations until a quaternary ammonium salt is formed. Considering...
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Preparation of 1° Amines: Azide Synthesis01:22

Preparation of 1° Amines: Azide Synthesis

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Direct alkylation of ammonia produces polyalkylated amines, along with a quaternary ammonium salt. To exclusively prepare primary amines, the azide synthesis method can be used.
Azide ions act as good nucleophiles and react with unhindered alkyl halides to form alkyl azides. Alkyl azides do not participate in further nucleophilic substitution reactions, thereby eliminating the chances of polyalkylated products. Alkyl azides are reduced by hydride-based reducing agents, like lithium aluminum...
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Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation02:24

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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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Alquilación enantioselectiva de enlaces primarios C-H en aminas terciarias de metilo habilitadas por el complejo de

Shanshan Yuan1, Sheng-Yu Li1, Xiao-Ming Zhao1

  • 1School of Chemical Science and Engineering, Tongji University, 1239 Siping Road, Shanghai, 200092 P.R. China.

Journal of the American Chemical Society
|November 27, 2024
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Resumen

Este estudio desarrolló un nuevo método para crear aminas quirales utilizando catalizadores de iridio. El proceso funciona en moléculas difíciles y se puede utilizar para modificar productos naturales como la bicuculina.

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Área de la Ciencia:

  • Química orgánica
  • Catálisis
  • Síntesis asimétrica

Sus antecedentes:

  • La funcionalización C ((sp3)-H enantioselectiva es crucial para la síntesis de moléculas quirales.
  • Las aminas terciarias son importantes motivos estructurales en productos farmacéuticos y naturales.
  • Los métodos anteriores lucharon con sustratos de aminas estéricamente obstaculizados o no activados.

Objetivo del estudio:

  • Desarrollar una inserción enantioselectiva de carbenos afinada en los enlaces primarios C ((sp3) -H.
  • Para permitir la síntesis de aminas quirales terciarias de sustratos difíciles.
  • Proporcionar un método versátil para la modificación de productos naturales.

Principales métodos:

  • Se utilizan catalizadores de porfirina de iridio quirales estéricamente exigentes.
  • Compuestos diazo utilizados para la inserción de carbenos en enlaces C (sp3) -H.
  • Mecanismos de reacción investigados utilizando el etiquetado con deuterio y la espectrometría de masas de alta resolución (HRMS).

Principales resultados:

  • Se obtienen altos rendimientos y excelentes enantioselectividades en la alquilación de aminas terciarias alifáticas desbloqueadas y no desactivadas de N-metilo.
  • Se aplicó con éxito el protocolo a la posmodificación de bicuculina quiral con alta diastereoselectividad.
  • Se ha demostrado una vía fácil para la derivación estereodivergente de productos naturales de alcaloides quirales.

Conclusiones:

  • El método desarrollado ofrece un avance significativo en la funcionalización enantioselectiva de C ((sp3) -H.
  • Este enfoque proporciona una herramienta valiosa para acceder a aminas quirales complejas y derivados de productos naturales.
  • Los conocimientos mecanicistas contribuyen a una comprensión más profunda de las reacciones de inserción de carbenos catalizados por iridio.