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Thermal and Photochemical Electrocyclic Reactions: Overview

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Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.

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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.

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Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.

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Updated: May 31, 2026

Efficient Construction of Drug-like Bispirocyclic Scaffolds Via Organocatalytic Cycloadditions of α-Imino γ-Lactones and Alkylidene Pyrazolones

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A remarkable multicomponent cascade sequence for the formation of a spirocyclic polyether.

Philip J Parsons¹, Noel Cooper, Matthew Renshaw

¹Department of Chemistry, School of Life Sciences, University of Sussex, Falmer, Brighton BN1 9QJ, UK. P.J.Parsons@sussex.ac.uk

Organic Letters

|June 25, 2011

Summary

Researchers synthesized a novel spirocyclic ether using a reaction involving 2-hydroxy-2-methylbutan-3-one and sodium hydride. This chemical synthesis provides a new route to complex cyclic compounds.

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Area of Science:

Organic Chemistry
Synthetic Chemistry

Background:

The synthesis of complex cyclic ethers is a fundamental area in organic chemistry.
Spirocyclic compounds possess unique structural and chemical properties.

Purpose of the Study:

To explore a novel synthetic route for spirocyclic ether formation.
To investigate the reaction of 2-hydroxy-2-methylbutan-3-one with sodium hydride.

Main Methods:

Reaction of 2-hydroxy-2-methylbutan-3-one with sodium hydride.
Use of ethyl formate as a potential reactant or additive.
Acid workup for product isolation.

Main Results:

Successful synthesis of the spirocyclic ether, designated as compound 3.
The reaction proceeded efficiently in the presence or absence of ethyl formate.

Conclusions:

A new method for synthesizing spirocyclic ethers has been established.
The reaction conditions are versatile, allowing for variations in the presence of ethyl formate.