Radical reactions of arenediazonium ions: An easy entry into the

Chem. Rev. 1988. 88. 765-792

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Radical Reactions of Arenediazonium Ions: An Easy Entry into the Chemistry of the Aryl Radical CARLO GALL1

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Ceniro di studio sui Maccanismi di Reazione del CNR, Diparlimenio di Chimica. Univemiia "La Sapienza 00 185 Roma. Italy Received July

Contents I. Introduction 11. Evolution of the Mechanistic View of the Diazonium Group Replacement 111. Homolytic Dediazoniation Reactions: A General Description A. How the Homolytic Dediazonlation Takes Place 1. Reduction at the Electrode 2. Radiolytic Approach 3. Photoinduced Electron Transfer 4. Reduction by Metal Cations 5. Anion-Induced Dedazoniation 6. Solvent-Induced Dediazoniation 7. Summary B. Product Patterns of the Aryl Radical 1. Hydrogen Atom Abstraction (Hydro-dediazoniation) 2. Reaction with X- (Halo-dediazoniation) 3. Other Sandmeyer-like Reactions 4. Addition to Olefins 5. Arylation of Aromatic Compounds 6. Conclusions IV. Related Reactions A. Intermediacy of the Aryl Radical 1. Reactions of Diaryliodonium Ions 2. S,,1 Reactions 8. Interchange of Product Patterns V. Unrelated Reactions VI. Acknowledgment VII. References

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I . Introduction The reactions of arenediazonium ions, ArN2+,have aroused mechanistic curiosity since the beginning of their extensive use in preparative chemistry. The present review will cover those processes where the diazo group is lost, that is, the dediazoniationreactions. These may take place, as we now understand them, either by a heterolytic (eq la) or by a homolytic (eq lb) mechanism or also via an aryne intermediate (Scheme