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Cycloaddition Reactions: Overview

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 Activation

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.

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

[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.

Cycloaddition Reactions: MO Requirements for Photochemical Activation

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.

Pericyclic Reactions: Introduction

Pericyclic Reactions: Introduction

Pericyclic reactions are organic reactions that occur via a concerted mechanism without generating any intermediates. The reactions proceed through the movement of electrons in a closed loop to form a cyclic transition state, where rearrangement of the σ and π bonds yields specific products.
Pericyclic reactions can be classified into three categories: electrocyclic reactions, cycloaddition reactions, and sigmatropic rearrangements. Electrocyclic reactions and sigmatropic rearrangements are...

Cyclohexenones via Michael Addition and Aldol Condensation: The Robinson Annulation

Cyclohexenones via Michael Addition and Aldol Condensation: The Robinson Annulation

Robinson annulation is a base-catalyzed reaction for the synthesis of 2-cyclohexenone derivatives from 1,3-dicarbonyl donors (such as cyclic diketones, β-ketoesters, or β-diketones) and α,β-unsaturated carbonyl acceptors. Named after Sir Robert Robinson, who discovered it, this reaction yields a six-membered ring with three new C–C bonds (two σ bonds and one π bond).

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Related Experiment Video

Updated: Jun 3, 2026

Preparation of a Corannulene-functionalized Hexahelicene by Copper(I)-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units

Preparation of a Corannulene-functionalized Hexahelicene by Copper(I)-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units

Published on: September 18, 2016

Recent advances in [2+2+2] cycloaddition reactions.

Gema Domínguez¹, Javier Pérez-Castells

¹Departamento de Química, Facultad de Farmacia, Universidad San Pablo-CEU, Boadilla del Monte, 28668-Madrid, Spain.

Chemical Society Reviews

|March 25, 2011

Summary

This summary is machine-generated.

The [2+2+2] cycloaddition reaction efficiently synthesizes aromatic compounds using various metal catalysts. This review highlights recent advances and applications in creating complex molecules, including natural products.

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Area of Science:

Organic Chemistry
Organometallic Chemistry
Synthetic Chemistry

Background:

The [2+2+2] cycloaddition is a powerful atom-efficient method for synthesizing carbocycles and heterocycles.
This reaction involves forming multiple carbon-carbon bonds in a single step, often yielding aromatic structures.
Numerous organometallic complexes, featuring over 15 different metals, catalyze cyclotrimerization reactions.

Purpose of the Study:

To provide a tutorial review of recent advancements in [2+2+2] cycloaddition reactions.
To encourage the utilization of this reaction for the synthesis of complex molecular architectures.
To summarize common catalysts, reaction conditions, and mechanistic insights.

Main Methods:

Surveying recent literature on [2+2+2] cycloaddition reactions.
Discussing cyclotrimerization of alkynes and nitriles, with emphasis on asymmetric variants.
Reviewing reactions involving double bonds and their applications.

Main Results:

Recent progress in [2+2+2] cycloaddition catalysis and scope has been detailed.
Mechanistic features of the reaction have been summarized.
Exemplary syntheses of natural products utilizing this methodology are presented.

Conclusions:

The [2+2+2] cycloaddition remains a versatile and efficient tool for constructing complex organic molecules.
Recent advances have expanded its utility, particularly in asymmetric synthesis and natural product total synthesis.
This review aims to inspire further exploration and application of this key reaction.