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Related Concept Videos

Cycloaddition Reactions: MO Requirements for Photochemical Activation01:12

Cycloaddition Reactions: MO Requirements for Photochemical Activation

2.4K
Some cycloaddition reactions are activated by heat, while others are initiated by light. For example, a [2 + 2] cycloaddition between two ethylene molecules occurs only in the presence of light. It is photochemically allowed but thermally forbidden.
2.4K
Cycloaddition Reactions: Overview01:16

Cycloaddition Reactions: Overview

3.2K
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.
3.2K
Cycloaddition Reactions: MO Requirements for Thermal Activation01:16

Cycloaddition Reactions: MO Requirements for Thermal Activation

4.0K
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.
4.0K
[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction01:16

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

11.9K
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.
11.9K
Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

2.1K
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
2.1K
Electrophilic 1,2- and 1,4-Addition of X2 to 1,3-Butadiene01:14

Electrophilic 1,2- and 1,4-Addition of X2 to 1,3-Butadiene

3.2K
Electrophilic addition of halogens to alkenes proceeds via a cyclic halonium ion to form a 1,2-dihalide or a vicinal dihalide.
3.2K

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Cercosporin-Photocatalyzed [4+1]- and [4+2]-Annulations of Azoalkenes Under Mild Conditions
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Visible-Light-Mediated Heterocycle Functionalization via Geometrically Interrupted [2+2] Cycloaddition.

Mihai V Popescu1, Aroonroj Mekereeya1, Juan V Alegre-Requena2

  • 1Chemistry Research Laboratory, University of Oxford, 12 Mansfield Road, Oxford, OX1 3TA, UK.

Angewandte Chemie (International Ed. in English)
|August 29, 2020
PubMed
Summary

Researchers developed a new photochemical method using blue LED light and an iridium complex to efficiently create fused γ-lactam structures. This interrupted [2+2] cycloaddition offers a novel route to valuable bicyclic compounds.

Keywords:
density functional calculationsenergy transferhomogeneous catalysisphotochemistryvisible light

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Area of Science:

  • Photochemistry
  • Organic Synthesis
  • Catalysis

Background:

  • The [2+2] photocycloaddition is a significant and well-studied photochemical reaction.
  • Fused γ-lactams are important structural motifs in organic chemistry.

Purpose of the Study:

  • To develop an efficient method for synthesizing fused γ-lactams using visible light photocatalysis.
  • To explore the mechanism of this novel photochemical transformation.

Main Methods:

  • Irradiation of N-acryloyl heterocycles with blue LED light (440 nm).
  • Use of an iridium(III) complex as a photocatalyst.
  • Quantum chemical calculations to elucidate the reaction mechanism.

Main Results:

  • Efficient and high-yielding formation of fused γ-lactams from various substituted heterocycles.
  • Demonstration of a reaction pathway involving triplet excited state cyclization, intersystem crossing, and a prototropic shift.
  • Identification of the key role of amide planarity in preventing cyclobutane formation.

Conclusions:

  • The developed method provides a novel and efficient route to fused γ-lactams via an interrupted [2+2] cycloaddition pathway.
  • The study elucidates the mechanistic details, highlighting the importance of excited state dynamics and structural constraints.