Meerwein arylation intramolecular

Cyclizations of aromatic diazonium salts138 (intramolecular Meerwein arylations) are pieparatively related to atom transfer reactions because a radical cyclization is terminated by the transfer of an atom or group other than hydrogen. However, the two methods are not mechanistically related. In the atom transfer method, the atom that is transferred to the cyclic product always derives from the radical precursor, but in the cyclizations of aryldiazonium salts, die atom or group transferred derives from an added reagent. This means that many different products can be prepared from a single diazonium precursor, but it... 

There are some reactions in which an aryl radical reacts with an sp2-carbon atom of an aliphatic side chain. In such reactions a carbo- or heteroalicyclic ring fused with a benzene ring is formed (Scheme 10-80). They may be called intramolecular Meerwein reactions. Techniques for these syntheses were developed by Beckwith s group in the 1980s. The majority of Beckwith s investigations were made with 2-(2 -propenyloxy)- and 2[(2 -methyl-2 -propenyl)oxy]benzenediazonium tetrafluoro-... 

In this section we include the intramolecular arylation of the Pschorr type, the inter-molecular arylation (Gomberg-Bachmann reaction), the arylation of alkenes and alkynes (Meerwein reaction) and related processes. 

The addition of aryl radicals, generated by chemical reduction of aryldiazonium salts, onto arenes in the Gomberg-Hey reaction is well established [163]. The addition of these radicals to alkenes in the Meerwein reaction is also well known [164], Aryl o-radicals generated by electrochemical reduction of aryl halides take part in similar reactions. Good yields of the products are obtained when the intermediate phenyl radical can react in an intramolecular manner. The addition step is then fast and competes successfully with further electron transfer to form the phenyl car-banion, followed by protonation. 

Indoles and Carbazoles. - Formation. 2-Arylindoles (132) are formed by intramolecular Wittig reaction of the phosphonium salts (131). The hydroxamic acids PhN(OH)COCH2COR (R = alkyl or aryl) cyclize in boiling toluene to mixtures of indoles (133) and 3-isoxazolones (134). Irradiation of a solution of o-iodoaniline and the potassium enolate of acetone affords 2-methylindole. The enamino-ketone (135) cyclizes photochemically to 1,2-dimethylindole (136) with elimination of acetaldehyde/ The styrene derivative (137), obtained by the action of Meerwein s acetal, Me2NCH(OMe)2, on o-nitrotoluene, yields 1-hydroxyindole on treatment with zinc/ Azidobenzocyclobutanes (138 R = Me, Ph, or CH2Ph) are converted into indoles (133) by the action of concentrated sulphuric acid/ ... 

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