Heterocyclic Diazo and Diazonium Compounds

The high reactivity of heterocyclic diazonium ions in azo coupling reactions is the reason why in some cases the primary diazotization products cannot be isolated. 2-Methyl-5-aminotetrazole 38, for example, yields directly the diazoamino compound 39 on diazotization, the intermediate diazonium ion being reactive enough to give the N-coupling product with the parent amine, even under strongly acidic conditions (22)60.61) 

The unsubstituted diazotetrazol 40 even couples with hydrazine in a manner not observed with benezenediazonium ions to form the hexazadiene 41 (23) 

An interesting example of how the reaction conditions can influence the structure of the product is given in (24). Depending on the acidity of the reaction medium and on the reaction time, the diazotization of aminotriazoles 42 yields the nitrosamines 43, the chlorb compounds 44, or the azo coupling product, i.e. the diazoamino compounds 45 

Most diazotized heterocyclic amines undergo normal coupling reactions with common aromatic coupling components, as well as with some C—H acidic compounds . This pertains for five-membered ring systems such as pyrrols 46 pyrazoles imidazoles 45 , l,2,4-(49) and 1,2,3-triazoles 50 

Reactions of potentially high synthetic utility are intramolecular azo coupling reactions of heterocyclic diazonium ions to give new fused-ring heterocycles. Some examples are given in (25-27) . The use of heterocyclic diazo compounds in organic synthesis has recently been reviewed by Ti ler and Stanovink , 

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