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Thermal Electrocyclic Reactions: Stereochemistry

Thermal Electrocyclic Reactions: Stereochemistry

The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
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.

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...

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.

Photochemical Electrocyclic Reactions: Stereochemistry

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

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.

Thermal and Photochemical Electrocyclic Reactions: Overview

Thermal and Photochemical Electrocyclic Reactions: Overview

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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Related Experiment Video

Updated: May 4, 2026

Design, Synthesis, and Photochemical Properties of Clickable Caged Compounds

Design, Synthesis, and Photochemical Properties of Clickable Caged Compounds

Published on: October 15, 2019

A click chemistry approach to secosteroidal macrocycles.

Malika Ibrahim-Ouali¹, Khalil Hamze¹

¹Aix Marseille Université, Centrale Marseille, CNRS, iSm2 UMR 7313, 13397 Marseille, France.

|December 24, 2013

Summary

Researchers developed a novel synthetic route for secosteroidal macrocycles using cycloaddition reactions. The study details the characteristic spectroscopic properties of these newly synthesized compounds.

Keywords:

1,2,3-Triazole Cholic acid Macrocycles ‘Click chemistry’

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Area of Science:

Organic Chemistry
Synthetic Chemistry
Medicinal Chemistry

Background:

Secosteroids are steroidal compounds that have undergone cleavage of one of the carbon-carbon bonds in their core structure.
Macrocyclic compounds are large ring structures that are of interest in various fields, including drug discovery.
The synthesis of complex molecular architectures like secosteroidal macrocycles presents significant challenges in organic chemistry.

Purpose of the Study:

To develop a new and efficient synthetic pathway for the construction of secosteroidal macrocycles.
To utilize cycloaddition reactions as a key step in the synthesis of these complex molecules.
To characterize the synthesized secosteroidal macrocycles using advanced spectroscopic techniques.

Main Methods:

A novel synthetic strategy employing cycloaddition reactions was designed and executed.
The reaction conditions were optimized to achieve efficient formation of the secosteroidal macrocycle core.
Nuclear Magnetic Resonance (NMR) spectroscopy, including proton (1H) and carbon-13 (13C) NMR, was used for structural elucidation.

Main Results:

A new synthetic pathway towards secosteroidal macrocycles was successfully established.
The key step in the synthesis involved a cycloaddition reaction, demonstrating its utility in forming the macrocyclic structure.
Detailed (1)H and (13)C NMR spectroscopic data for the synthesized compounds were obtained and reported, confirming their structures.

Conclusions:

The developed synthetic pathway provides a viable method for accessing secosteroidal macrocycles.
Cycloaddition reactions are effective for the construction of these complex molecular frameworks.
The reported spectroscopic characterization aids in the identification and further study of these compounds.