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Related Concept Videos

Cycloaddition Reactions: Overview01:16

Cycloaddition Reactions: Overview

3.7K
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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[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.
12.9K
Woodward–Hoffmann Selection Rules and Microscopic Reversibility01:34

Woodward–Hoffmann Selection Rules and Microscopic Reversibility

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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...
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Cycloaddition Reactions: MO Requirements for Thermal Activation01:16

Cycloaddition Reactions: MO Requirements for Thermal Activation

4.9K
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

3.1K
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.
3.1K
Thermal Electrocyclic Reactions: Stereochemistry01:17

Thermal Electrocyclic Reactions: Stereochemistry

2.6K
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.
2.6K

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Cercosporin-Photocatalyzed [4+1]- and [4+2]-Annulations of Azoalkenes Under Mild Conditions
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Natural [4 + 2]-Cyclases.

Byung-Sun Jeon1, Shao-An Wang1, Mark W Ruszczycky1

  • 1Department of Chemistry and ‡Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy, University of Texas at Austin , Austin, Texas 78712, United States.

Chemical Reviews
|April 27, 2017
PubMed
Summary
This summary is machine-generated.

Enzymes catalyze Diels-Alder (or [4+2]) cycloadditions in natural product biosynthesis, accelerating reactions and controlling stereochemistry. Ongoing research reveals insights into their function, catalysis, and evolutionary origins.

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Area of Science:

  • Biochemistry
  • Organic Chemistry
  • Natural Product Synthesis

Background:

  • Diels-Alder ([4+2]) cycloadditions are crucial in synthesizing complex natural products.
  • Enzymes involved in these pathways are known to enhance reaction rates and stereochemical control.
  • Mechanistic studies of these enzymes are still in early stages.

Purpose of the Study:

  • To explore the role of enzymes in [4+2] cycloadditions within natural product biosynthesis.
  • To investigate the catalytic mechanisms and evolutionary origins of these enzymes.
  • To provide new insights into the biosynthetic pathways of complex natural products.

Main Methods:

  • Literature review of recent studies on biosynthetic enzymes.
  • Analysis of known Diels-Alder ([4+2]) cycloaddition reactions in nature.
  • Comparative analysis of enzyme mechanisms and evolutionary data.

Main Results:

  • Enzymes significantly accelerate [4+2] cycloaddition rates in natural product biosynthesis.
  • Enzymes impose precise stereochemical control over the cycloaddition reactions.
  • Recent studies offer novel perspectives on enzyme function and origin.

Conclusions:

  • Enzymes play a vital role in facilitating and controlling key cycloaddition reactions in natural product synthesis.
  • Understanding these enzymes provides insights into biosynthetic strategies and enzyme evolution.
  • Further mechanistic studies are essential for a comprehensive understanding.