Erminia Del Vecchio

Tetrahalogenomethanes: simple reagents for the synthesis of monohalogenated and mixed dihalogenated aromatic heterocycles via metal–halogen exchange from lithium compounds

Abstract Tetrabromo- or tetrachloromethane and 2-lithio derivatives of aromatic heterocycles rapidly produce the corresponding 2-bromo or 2-chloro derivatives in high yields through a metal–halogen exchange mechanism. This kind of reaction was also used to obtain, in good yields, 5-bromo-2-chlorothiazole and 5-bromo-2-chloro-N-methylimidazole.

Arenediazonium o‐Benzenedisulfonimides: Some Kinetics of Azo Coupling Reactions with Naphthols

Kinetic investigation of azo coupling reactions between naphthols and 4-methoxy- and 4-nitrobenzenediazonium o-benzenedisulfonimides has been carried out for comparison with the related benzenediazonium tetrafluoroborates. The data clearly indicate that the two kinds of diazonium salts show very similar reactivities. This fact emphasizes that arenediazonium o-benzenedisulfonimides, which are very stable, may be used as alternatives to the more usual diazonium salts. The azo coupling reactions between 4-nitro- and 4-methoxybenzenediazonium salts and 1-bromo-2-naphthol, performed with equimolecular amounts of both reagents, showed the unexpected formation of large amounts of 1-bromo-4-nitrobenzene and 1-bromo-4-methoxybenzene. Some mechanistic implications of this behaviour are discussed. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Ring Closure of Azo Compounds to 1,2-Annulated Benzimidazole Derivatives and Further Evidence of Reversibility of the Azo-Coupling Reaction

The reaction between 1,3,5-tris(N,N-dialkylamino)benzene derivatives and 2 equiv of p-substituted benzenediazonium salts gives dicationic species which collapse to new benzimidazole derivatives with expulsion of p-substituted anilines. The presence of electron-withdrawing groups on the benzenediazo moiety of the dicationic species plays a key role in this unexpected ring closure reaction. The observed chemical behavior has been rationalized in terms of the already reported reversibility of azo coupling reactions and provided further evidence for it.