Arenediazonium salt aryl iodides from

Arylamines are converted by diazotization with nitrous acid into arenediazonium salts, ArN2+ X-. The diazonio group can then be replaced by many other substituents in the Sandmeyer reaction to give a wide variety of substituted aromatic compounds. Aryl chlorides, bromides, iodides, and nitriles can be prepared from arenediazonium salts, as can arenes and phenols. In addition to their reactivity toward substitution reactions, diazonium salts undergo coupling with phenols and arylamines to give brightly colored azo dyes. 

Such a mechanism was unlikely as addition of an external trap, 1,1-diphenylethylene, had no effect on the course of the arylation of p-ketoesters.i l A second approach involved the use of an internal trapping system which had been successfully used in the study of the radical reactions of arenediazonium salts.The internal trap containing reagent, ( rf/io-allyloxyphenyl)lead triacetate (94), can be easily prepared from the corresponding boronic acid. 2 Reaction with various types of nucleophiles, such as ethyl 2-oxocyclopentanecarboxylate (86), mesitol (36), the sodium salt of nitropropane, iodide and azide always afforded the C-arylation products in high yield. No trace of the 3-substituted dihydrobenzofurans, expected in a mechanism involving the intermediacy of free radicals, could be detected. 

In the initial demonstration of this concept, the aryl radical was obtained by the classic tin method (eq 2). Subsequently, by changing the radical precursor from a halogen to a diazonium ion and working in the presence of an appropriate source of electrons, it was possible to carry out the homolytic displacement reaction under stannane-free, nonreductive conditions. The method is based on work from the Beckwith laboratory, in which it was demonstrated that arenediazonium salts in the presence of electron donors, such as iodide and thiolate ions, can generate aryl radicals in a facile, clean reaction. 

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