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Related Concept Videos

Cycloaddition Reactions: MO Requirements for Photochemical Activation01:12

Cycloaddition Reactions: MO Requirements for Photochemical Activation

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.
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.
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.
Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

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
Oxidation of Alkenes: Anti Dihydroxylation with Peroxy Acids02:04

Oxidation of Alkenes: Anti Dihydroxylation with Peroxy Acids

Diols are compounds with two hydroxyl groups. In addition to syn dihydroxylation, diols can also be synthesized through the process of anti dihydroxylation. The process involves treating an alkene with a peroxycarboxylic acid to form an epoxide. Epoxides are highly strained three-membered rings with oxygen and two carbons occupying the corners of an equilateral triangle. This step is followed by ring-opening of the epoxide in the presence of an aqueous acid to give a trans diol.
[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.

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Updated: Jun 12, 2026

[(DPEPhos)(bcp)Cu]PF6: A General and Broadly Applicable Copper-Based Photoredox Catalyst
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[(DPEPhos)(bcp)Cu]PF6: A General and Broadly Applicable Copper-Based Photoredox Catalyst

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[2+2] cycloadditions by oxidative visible light photocatalysis.

Michael A Ischay1, Zhan Lu, Tehshik P Yoon

  • 1Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, USA.

Journal of the American Chemical Society
|June 10, 2010
PubMed
Summary

Ruthenium tris(bipyridine) (Ru(bpy)(3)(2+)) efficiently catalyzes [2+2] cycloadditions for both electron-rich and electron-deficient olefins. This versatile photocatalyst enables strained ring synthesis using visible light.

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Light-driven Enzymatic Decarboxylation
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Light-driven Enzymatic Decarboxylation
09:58

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Published on: May 22, 2016

Area of Science:

  • Organic Chemistry
  • Photochemistry
  • Catalysis

Background:

  • Photochemical reactions are valuable for synthesizing strained ring systems, such as cyclobutanes.
  • Ruthenium tris(bipyridine) (Ru(bpy)(3)(2+)) has been previously established as an effective photocatalyst for [2+2] cycloadditions involving electron-deficient olefins.

Purpose of the Study:

  • To demonstrate the efficacy of Ru(bpy)(3)(2+) as a photocatalyst for the [2+2] cycloaddition of electron-rich olefins.
  • To highlight the versatile photoelectrochemical properties of Ru(bpy)(3)(2+) in organic synthesis.

Main Methods:

  • Utilized visible light irradiation in the presence of Ru(bpy)(3)(2+).
  • Investigated the [2+2] cycloaddition reactions of electron-rich olefins.
  • Leveraged the photoelectrochemical capabilities of the photocatalyst for one-electron reduction or oxidation.

Main Results:

  • Ru(bpy)(3)(2+) effectively catalyzes the [2+2] cycloaddition of electron-rich olefins.
  • The photocatalyst demonstrates versatility by facilitating reactions through either one-electron reduction or oxidation pathways.

Conclusions:

  • Ru(bpy)(3)(2+) is a versatile photocatalyst for [2+2] cycloadditions of both electron-deficient and electron-rich olefins.
  • This expands the utility of Ru(bpy)(3)(2+) in constructing strained ring systems via visible-light photochemistry.