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An unusual radical Smiles rearrangement
Eric Bacqué1, Myriem El Qacemi, Samir Z Zard
1Laboratoire de Synthèse Organique associé au CNRS, Ecole Polytechnique, 91128 Palaiseau, France.
Organic Letters
|August 12, 2005
Summary
This study reveals a new Smiles rearrangement mechanism involving a four-membered ring for specific radicals. This process can also lead to unprecedented isocyanate fragmentation under moderate heating conditions.
Area of Science:
- Organic Chemistry
- Reaction Mechanisms
- Radical Chemistry
Background:
- The Smiles rearrangement is a known nucleophilic aromatic substitution reaction.
- Radical-mediated reactions offer alternative pathways for molecular transformations.
Purpose of the Study:
- To investigate the radical-induced Smiles rearrangement of N-(alpha-xanthyl)acetanilides and N-(alpha-xanthyl)acetylaminopyridines.
- To characterize the reaction intermediates and products, including novel fragmentation pathways.
Main Methods:
- Generation of radicals from N-(alpha-xanthyl)acetanilides and N-(alpha-xanthyl)acetylaminopyridines.
- Analysis of reaction products using spectroscopic techniques.
- Mechanistic studies to elucidate the rearrangement pathway.
Main Results:
- A novel Smiles rearrangement proceeding through a four-membered ring intermediate was discovered.
- Amidyl radicals, formed from the cleavage of the four-membered ring, were observed to fragment into isocyanates.
- Isocyanate formation via fragmentation was unprecedented at temperatures relevant to refluxing benzene or chlorobenzene.
Conclusions:
- The study presents a new radical-mediated Smiles rearrangement mechanism.
- A novel fragmentation pathway for amidyl radicals leading to isocyanates under moderate conditions has been identified.
- These findings expand the known scope of the Smiles rearrangement and radical reaction chemistry.