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Related Concept Videos

Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

1.8K
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
1.8K
Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

2.3K
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.
2.3K
Thermal Electrocyclic Reactions: Stereochemistry01:17

Thermal Electrocyclic Reactions: Stereochemistry

2.0K
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.
2.0K
Diels–Alder Reaction Forming Cyclic Products: Stereochemistry01:28

Diels–Alder Reaction Forming Cyclic Products: Stereochemistry

3.7K
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.
3.7K
Diels–Alder Reaction Forming Bridged Bicyclic Products: Stereochemistry01:29

Diels–Alder Reaction Forming Bridged Bicyclic Products: Stereochemistry

4.6K
Diels–Alder reactions between cyclic dienes locked in an s-cis configuration and dienophiles yield bridged bicyclic products.
4.6K
Stereochemical Effects of Enolization01:12

Stereochemical Effects of Enolization

2.0K
The chiral α-carbon of the carbonyl compound is the stereocenter of the molecule. As shown in the figure below, when such a carbonyl compound undergoes racemization under an acidic or basic condition, an achiral enol is formed.
2.0K

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Updated: May 23, 2025

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Deconjugative Photoisomerization of Cyclic Enones.

Lukas Blank1, Jungwon Kim2, Constantin G Daniliuc1

  • 1Institute for Organic Chemistry, University of Münster, Corrensstraβe 36, Münster 48149, Germany.

Journal of the American Chemical Society
|March 7, 2025
PubMed
Summary

This study introduces a simple photochemical method for isomerizing cyclic enones, enabling the creation of valuable regioisomeric products. The new technique uses near-UV light and a Brønsted acid catalyst for efficient alkene reactivity Umpolung.

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Area of Science:

  • Organic Chemistry
  • Photochemistry
  • Catalysis

Background:

  • Deconjugative isomerization of α,β-unsaturated carbonyl compounds is a powerful synthetic tool.
  • Challenges include endergonic processes, regioselectivity control, and underdeveloped methods for cyclic enones.
  • Existing methods often require harsh conditions, have limited scope, or lack mechanistic understanding.

Purpose of the Study:

  • To develop an operationally simple photochemical method for the deconjugative isomerization of cyclic enones.
  • To expand the substrate scope for this transformation, including industrially relevant compounds.
  • To elucidate the reaction mechanism, highlighting the role of solvent and radical intermediates.

Main Methods:

  • Photochemical isomerization using near-UV (372 nm) irradiation.
  • Catalysis with a Brønsted acid (HCl).
  • Mechanistic investigations including solvent effects and kinetic studies.

Main Results:

  • Successful exocyclic deconjugative isomerization of a diverse range of cyclic enones.
  • Demonstrated applicability to α-isophorone, terpenoids, and steroids.
  • Identified solvent as a key mediator and proposed a mechanism involving sequential hydrogen atom transfer (HAT) and reverse-HAT (RHAT).

Conclusions:

  • The developed photochemical platform offers a practical and efficient route for cyclic enone isomerization.
  • The findings provide mechanistic insights into the role of solvent and radical pathways.
  • This method broadens synthetic possibilities for accessing regioisomeric carbonyl compounds.