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Related Concept Videos

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.
[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.
Aromatic Hydrocarbon Cations: Structural Overview01:18

Aromatic Hydrocarbon Cations: Structural Overview

Cycloheptatriene is a neutral monocyclic unsaturated hydrocarbon that consists of an odd number of carbon atoms and an intervening sp3 carbon in the ring. The three double bonds in the ring correspond to 6 π electrons, which is a Huckel number, and therefore satisfies the criteria of 4n + 2 π electrons. However, the intervening sp3 carbon disrupts the continuous overlap of p orbitals. As a result, cycloheptatriene is not aromatic.
Removing one hydrogen from the intervening CH2 group with both...
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.
Criteria for Aromaticity and the Hückel 4n + 2 Rule01:20

Criteria for Aromaticity and the Hückel 4n + 2 Rule

Like benzene, cyclobutadiene and cyclooctatetraene are cyclic compounds with alternate single and double bonds. However, their chemical behavior differs from benzene, as they are unstable and not aromatic. So, what are the structural characteristics of unsaturated compounds categorized as aromatic?
For the first time, Eric Hückel, a German chemical physicist, derived a set of structural features for a compound to be classified as aromatic. This is now known as Hückel’s rule or the 4n + 2 rule.
Nomenclature of Alkynes02:39

Nomenclature of Alkynes

Alkynes are unsaturated hydrocarbons characterized by the presence of carbon-carbon triple bonds and have a general formula CnH2n-2. The nomenclature of alkynes follows a set of rules similar to alkanes and alkenes; however, alkynes bear the suffix "-yne" instead of "-ane" or "-ene." There are two approaches to naming alkynes:

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Helical Topologies via [4 + 2] Cycloaddition Reactions between Structurally Complex Benzynes and Several Alkenyl

Rong Tang1, Trinadh Kaicharla1, Thomas R Hoye1

  • 1Department of Chemistry, University of Minnesota, 207 Pleasant Street, SE, Minneapolis, Minnesota 55455, United States.

Organic Letters
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Summary

This study explores reactions between vinyl-substituted arenes and benzynes, forming complex polycyclic products with helical structures. These reactions showcase intriguing reactivity, including atom-economical pathways for intricate molecule synthesis.

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Area of Science:

  • Organic Chemistry
  • Synthetic Chemistry
  • Polycyclic Aromatic Hydrocarbons

Background:

  • Vinyl-substituted arenes and benzynes are key building blocks in organic synthesis.
  • Hexadehydro-Diels-Alder (HDDA) reactions offer pathways to complex molecular architectures.
  • Understanding the reactivity of dearomatized adducts is crucial for developing new synthetic methodologies.

Purpose of the Study:

  • To investigate the reactions of various vinyl-substituted arenes with benzynes.
  • To explore the formation of complex polycyclic products with helical topologies.
  • To elucidate the mechanistic pathways and reactivity of the initial adducts.

Main Methods:

  • Generation of benzynes via thermal cycloisomerization of triyne substrates using hexadehydro-Diels-Alder (HDDA) reaction.
  • Reaction of in-situ generated benzynes with vinyl-substituted arenes (phenyl, 2-naphthyl, 9-phenanthryl, 2-triphenylenyl).
  • Exploration of reactions involving indene and benzofuran.

Main Results:

  • Formation of structurally complex, polycyclic products with helical topologies.
  • Observation of unexpected reactivity modes in initial [4 + 2] dearomatized adducts, including ene reactions, [2 + 2] cycloadditions, and autoxidation.
  • Demonstration of significant complexity-building, with up to five new rings formed in some cases.
  • Identification of fully atom-economical transformations.

Conclusions:

  • The reaction of vinyl-substituted arenes with benzynes provides access to intricate polycyclic molecules with helical structures.
  • The observed reactivity highlights novel mechanistic pathways and the potential for cascade reactions.
  • These findings contribute to the development of efficient and atom-economical synthetic strategies for complex molecule construction.