Imidazole Chichibabin reaction

Amines are insufficiently nucleophilic to react with most azoles which do not contain a ring oxygen, and the stronger nucleophile NH2 is required. When treated with amide ions, thiazoles can be aminated in the 2-position by NaNHa at 150 °C. Only TV-substituted condensed imidazoles such as 1-alkylbenzimidazole react in such Chichibabin reactions. Imidazoles are aminated by alkaline NH2OH. 

Chichibabin reaction, 5, 409-410 UV spectra, 5, 356 Naphthimidazoles, 2-amino-tautomerism, 5, 368 Naphth[2,3-h]imidazoles oxidation, 5, 405 Naphth[l,2-d]imidazolium salts nucleophilic substitution, 5, 412 Naphth[l, 2-h]isoquinolines... 

In general, the 1,3-diazoles do not react by nucleophilic substitution, although imidazole can participate in the Chichibabin reaction with substitution at C-2 the position of substitution is eqmvalent to that noted with pyridine (see Section 11.4.1). Nucleophilic species that are strong bases, like... 

Only condensed imidazoles will enter into the Chichibabin reaction.406 Sulfo groups on C-2 of benzimidazoles are replaced by chloro,407 cyano,408 hydroxy,409 410 and alkylamino groups,411 and the... 

The Chichibabin reaction with imidazoles has been the subject of extensive study in the U.S.S.R. (82CHE1221). Criteria for successful amination require that the imidazole ring be condensed with an aromatic system at the 4-and 5-positions, and that the pyrrole nitrogen be substituted (Scheme 72) (73CHE88). Another requirement is that the heterocycle must have a pK, of at least 4.3 for heterogeneous aminations. The parent compound, imidazole, substituted in the 1-position, does not undergo the Chichibabin reaction. Even substituted imidazoles such as phenanthro[9,10-d] imidazole (204) do not aminate (73CHE88). 

Nucleophiles react faster with benzimidazoles than with imidazoles, the attack occurring at the 2-position. For instance, on treatment with sodium amide in xylene, 1-alkylbenzimidazoles give the corresponding 2-amino compounds (Chichibabin reaction, see p 278). 

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