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Cercosporin-Photocatalyzed [4+1]- and [4+2]-Annulations of Azoalkenes Under Mild Conditions
Published on: July 17, 2020
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Photosensitized [2 + 2]-Cycloaddition of Complex Acceptor-Donor Combinations: A Regio/Diastereoselectivity Study
Jens Lefarth1, Axel G Griesbeck1
1Department of Chemistry, University of Cologne, 50939 Köln, Germany.
The Journal of Organic Chemistry
|June 1, 2022
Summary
Photosensitized [2 + 2]-cycloaddition reactions involving chalcones and enones were studied. Reaction conditions can control the complex product mixtures formed with electron-rich alkenes.
Area of Science:
- Organic Chemistry
- Photochemistry
- Cycloaddition Reactions
Background:
- The [2 + 2]-cycloaddition is a fundamental reaction in organic synthesis.
- Chalcones and conjugated enones are versatile building blocks.
- Controlling selectivity in photochemical reactions remains a challenge.
Purpose of the Study:
- To investigate the photosensitized [2 + 2]-cycloaddition of chalcones and conjugated enones with electron-rich alkenes.
- To understand the factors influencing regio- and stereoselectivity.
- To explore methods for controlling complex product mixtures.
Main Methods:
- Photosensitized [2 + 2]-cycloaddition reactions.
- Use of various chalcones, cyclic enones (cyclopentenones, cyclohexenones), and acyclic enones.
- Employing electron-rich alkenes like cyclic enolethers and polymethylated alkenes.
- Analysis of reaction products to determine regio- and stereoisomers.
Main Results:
- Cyclic enones exhibited high regio- and stereoselectivity in the cycloaddition.
- Acyclic enones yielded complex product mixtures, including dimers and four major regio- and diastereoisomers.
- The selectivity of the reaction with acyclic enones could be modulated by reaction conditions.
Conclusions:
- The photosensitized [2 + 2]-cycloaddition offers a pathway to complex cyclic structures.
- Cyclic enones provide a more predictable outcome compared to acyclic enones.
- Optimization of reaction parameters (sensitizer, solvent, additives) is crucial for controlling product distribution in challenging cycloadditions.
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