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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.

[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 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.

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.

Preparation and Reactions of Sulfides

Preparation and Reactions of Sulfides

Sulfides are the sulfur analog of ethers, just as thiols are the sulfur analog of alcohol. Like ethers, sulfides also consist of two hydrocarbon groups bonded to the central sulfur atom. Depending upon the type of groups present, sulfides can be symmetrical or asymmetrical. Symmetrical sulfides can be prepared via an SN2 reaction between 2 equivalents of an alkyl halide and one equivalent of sodium sulfide.

Diels–Alder Reaction Forming Cyclic Products: Stereochemistry

Diels–Alder Reaction Forming Cyclic Products: Stereochemistry

The Diels–Alder reaction is one of the robust methods for synthesizing unsaturated six-membered rings. The reaction involves a concerted cyclic movement of six π electrons: four π electrons from the diene and two π electrons from the dienophile.

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Related Experiment Video

Updated: Dec 7, 2025

Facile Preparation of 2Z,4E-Dienamides by the Olefination of Electron-deficient Alkenes with Allyl Acetate

Facile Preparation of 2Z,4E-Dienamides by the Olefination of Electron-deficient Alkenes with Allyl Acetate

Published on: June 21, 2017

Small Molecule Activation by Two-Coordinate Acyclic Silylenes.

Shiori Fujimori¹, Shigeyoshi Inoue¹

¹Department of Chemistry WACKER-Institute of Silicon Chemistry and Catalysis Research Center Technische Universität München Lichtenbergstraße 4 85748 Garching bei München Germany.

European Journal of Inorganic Chemistry

|October 1, 2020

Summary

Stable silylenes have advanced significantly, with recent breakthroughs in two-coordinate acyclic silylenes enabling small molecule activation. These reactive compounds, including N-heterocyclic silylenes, are expanding chemical possibilities.

Keywords:

Acyclic compounds Reaction mechanisms Silicon Silylenes Small molecule activation

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Imine Metathesis by Silica-Supported Catalysts Using the Methodology of Surface Organometallic Chemistry

Imine Metathesis by Silica-Supported Catalysts Using the Methodology of Surface Organometallic Chemistry

Published on: October 18, 2019

Area of Science:

Organosilicon Chemistry
Main Group Chemistry
Reactive Intermediates

Background:

Silylene chemistry has seen major advancements since the isolation of silicocene in 1986 and N-heterocyclic silylenes in 1994.
Significant progress has been made in synthesizing cyclic and higher-coordinated silicon(II) compounds.
The isolation of the first two-coordinate acyclic silylene in 2012 marked a new era in silylene research.

Purpose of the Study:

To review the recent developments in silylene chemistry, focusing on two-coordinate acyclic silylenes.
To highlight the synthesis and properties of these highly reactive species.
To discuss their emerging applications in small molecule activation.

Main Methods:

Review of experimental studies on silylene synthesis and characterization.
Analysis of computational investigations into silylene reactivity.
Examination of silylene applications in chemical transformations.

Main Results:

The synthesis of isolable two-coordinate acyclic silylenes has been achieved.
These silylenes exhibit exceptionally high reactivity.
They have demonstrated utility in activating small molecules, including H2.

Conclusions:

Two-coordinate acyclic silylenes represent a significant advancement in main group chemistry.
Their unique reactivity opens new avenues for small molecule activation.
Further research into silylene chemistry promises novel catalytic applications.