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Related Concept Videos

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

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

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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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Cycloaddition Reactions: Overview01:16

Cycloaddition Reactions: Overview

2.4K
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.
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Preparation of Alkynes: Dehydrohalogenation02:34

Preparation of Alkynes: Dehydrohalogenation

17.1K
Introduction
Alkynes can be prepared by dehydrohalogenation of vicinal or geminal dihalides in the presence of a strong base like sodium amide in liquid ammonia. The reaction proceeds with the loss of two equivalents of hydrogen halide (HX) via two successive E2 elimination reactions.
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Cycloaddition Reactions: MO Requirements for Thermal Activation01:16

Cycloaddition Reactions: MO Requirements for Thermal Activation

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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.
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Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

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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.
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Electrophilic Addition to Alkynes: Halogenation02:38

Electrophilic Addition to Alkynes: Halogenation

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Introduction
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
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Preparation of a Corannulene-functionalized Hexahelicene by CopperI-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units
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Preparation of a Corannulene-functionalized Hexahelicene by CopperI-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units

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[2+2+1] cyclization of allenes.

S Kitagaki1, F Inagaki, C Mukai

  • 1Division of Pharmaceutical Sciences, Graduate School of Medical Sciences, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan. mukai@p.kanazawa-u.ac.jp.

Chemical Society Reviews
|February 12, 2014
PubMed
Summary
This summary is machine-generated.

The Pauson-Khand reaction, a [2+2+1] cyclization, is enhanced by using allenes. This review covers allenic cyclocarbonylation progress, chirality transfer, and synthetic uses.

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Area of Science:

  • Organic Chemistry
  • Synthetic Methodology

Background:

  • The Pauson-Khand reaction is a key method for synthesizing five-membered rings.
  • Traditional Pauson-Khand reactions involve alkynes and alkenes.
  • Allenes offer a versatile alternative to alkenes or alkynes in cyclocarbonylation.

Purpose of the Study:

  • To review the development of allenic [2+2+1] cyclocarbonylation.
  • To highlight the role of allene chirality in the reaction.
  • To explore the synthetic applications of this methodology.

Main Methods:

  • Literature review of allenic cyclocarbonylation reactions.
  • Analysis of stereochemical outcomes, focusing on chirality transfer.
  • Compilation of examples showcasing synthetic utility.

Main Results:

  • Allenes effectively participate in [2+2+1] cyclocarbonylation reactions.
  • Chirality present in the allene can be transferred to the product.
  • The reaction provides access to diverse cyclopentanone derivatives.

Conclusions:

  • Allenic cyclocarbonylation expands the scope of the Pauson-Khand reaction.
  • This method offers efficient routes to chiral cyclopentanones.
  • It represents a valuable tool in modern organic synthesis.