Tetrazole-ring formation

The tetrazole functionality has an important role in organic synthesis, medicinal chemistry, and various materials science applications. The simplest method to prepare this heterocyclic ring is the 1,3-dipolar cycloaddition of azides and nitriles. The reaction mechanism was recently revised.  

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Schemes Tetrazole ring formation from a resin-bound nitrile 319 with MesSiNj (146) and catalytic -Bu2SnO for 50 h at 90 °C in o-xylene [217,228]...

The thermolysis of l-([l,3,4]thiadiazol-2-yl)tetrazoles 133 gives rise to the loss of dinitrogen from the tetrazole ring and the formation of 2,6-diaryl[l,2,4]triazolo[5,l+][l,3,4]thiadiazoles 71 (Equation 39) <1985IJB908, 1990FA953>. (For another synthesis of compounds 71, see Section 11.07.8.1.5.)... 

Ring synthesis involving formation of the tetrazole ring via azide-tetrazole equilibrium 656... 

Ring synthesis including formation of the tetrazole ring by intramolecular 1,3-dipolar... 

In effect, antifoggants enhance the difference between the rate of formation of the desired image density and that of fog density. Many heterocyclic compounds have been claimed to restrain fog. These include suitably substituted benzotriazoles, benzimidazoles, indazoles, oxazoles, thiazoles, triazoles and tetrazoles. Heterocyclic compounds bearing a thiol substituent invariably show some antifoggant activity. Thus phenylmercaptotetrazole (16) which contains both a thiol group and a tetrazole ring is very effective (59MI11400). 

When heated with bases, the 2-azidopyrido[l,2- ]pyrimidine (102) yields pyridyltetrazoles (269 R = CONR R2). This reaction is initiated by nucleophilic addition of the base to the carbonyl group it is followed by ring opening between the C-4 and N-5 atoms and formation of the tetrazole ring involving the azido group and the N-l atom of the starting pyrido-pyrimidine.166 291... 

Reactions of alkyl substituents of the tetrazole ring relevant to the formation and transformations of vinyl groups at C-5 are considered in a review <2003RCR143> (cf. Section 6.07.7.2.7). 

The main reactions (A-G) and the corresponding pathways resulting in the formation, or subsequent functionalization, of tetrazole rings are shown in Scheme 83. As seen from the scheme, only several elementary reaction acts leading to a five-membered heteroaromatic ring with four nitrogen atoms (tetrazole ring) are possible. These reactions follow the mechanisms depicted in Scheme 83. These are ... 

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