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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.

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

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Updated: Dec 9, 2025

Constructing Cyclic Peptides Using an On-Tether Sulfonium Center

Constructing Cyclic Peptides Using an On-Tether Sulfonium Center

Published on: September 28, 2022

Photochemical Methods for Peptide Macrocyclisation.

Laetitia Raynal¹, Nicholas C Rose¹, James R Donald^1,2

¹Department of Chemistry, University of York, Heslington, York, YO10 5DD, UK.

Chemistry (Weinheim an Der Bergstrasse, Germany)

|September 11, 2020

Summary

This summary is machine-generated.

Photochemical macrocyclisation of peptides and small proteins offers enhanced stability and potency. This review covers established and emerging methods, highlighting opportunities for innovative therapeutic agents.

Keywords:

macrocyclisation peptides photochemistry

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Area of Science:

Organic Chemistry
Photochemistry
Medicinal Chemistry

Background:

Photochemical reactions have seen significant advancements in the last 20 years.
These methods are now applied to peptide and small protein macrocyclisation.
Macrocyclic peptides offer improved stability, rigidity, and biological activity compared to linear peptides.

Purpose of the Study:

To provide an overview of photochemical peptide macrocyclisation methods.
To highlight established and emerging techniques in the field.
To identify limitations and future opportunities for innovation.

Main Methods:

Review of literature on photochemical macrocyclisation techniques.
Analysis of established and novel synthetic strategies.
Discussion of the advantages and disadvantages of different methods.

Main Results:

Established photochemical methods enable peptide macrocyclisation.
Emerging techniques offer new possibilities for complex macrocycle synthesis.
Macrocyclic peptides demonstrate enhanced therapeutic potential.

Conclusions:

Photochemical macrocyclisation is a powerful tool for creating advanced peptide therapeutics.
Further innovation is needed to overcome current limitations.
The field holds significant promise for drug discovery and development.