Pschorr reaction mechanism

The Pschorr reaction can take place by two different mechanisms, depending on conditions (1) attack by an aryl radical (as in the Gomberg-Bachmann reaction) or (2) attack by an aryl cation (similar to the SnI mechanism discussed on p. 853). Under certain conditions the ordinary Gomberg-Bachmann reaction can also involve attack by aryl cations. 

Another free-radical arylation method consists of the photolysis of aryl iodides in an aromatic solvent. Yields are generally higher than in 14-17 or 14-21. The aryl iodide may contain OH or COOH groups. The mechanism is similar to that of 14-17. The aryl radicals are generated by the photolytic cleavage ArI AR + T. The reaction has been applied to intramolecular arylation (analogous to the Pschorr reaction). A similar reaction is photolysis of an arylthallium bis(trifluoroacetate) (12-21) in an aromatic solvent. Here too, an unsymmetrical biaryl is produced in good yields. ... 

The Pschorr reaction is a method of synthesis of phenanthrenes from diazotized Z-2-aminostilbenes. A traditional procedure involves heating with a copper catalyst. Improved yields are often observed, however, if the diazonium ion is treated with iodide ion. Suggest a mechanism for the iodide-catalyzed reaction. 

Studies on the mechanism of the Pschorr reaction have led to a number of interesting cyclizations onto a pyridine nucleus. Hey and Osbond441 were the first to carry out such a reaction 7,8-dihydro-benzo[/]quinoline (211) was obtained in 41 % yield from the N-nitroso-acetanilide (210). The diazonium salt of the amine 212 also underwent cyclization in spite of the presence of a second deactivating... 

Furthermore, the Pschorr reaction of the aminoisoquinoline 163 gave no expected product 164 but only the abnormal products isovanillin (165) and the isocarbostyril derivative 166, the mechanism of the... 

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