2.5- Disubstituted tetrazoles, thermolysis

A well-known reaction of tetrazoles is the thermolysis of 2,5-disubstituted tetrazoles to give nitrilimines by loss of N2 an example is shown in Scheme 4. The reaction is used not only for its synthetic potential but also as a source of nitrilimines for direct observation and exploration of their behavior. The first direct detection of a thermally generated nitrilimine was the species (31) produced by flash vacuum pyrolysis of 5-phenyl-2-trimethylsilyltetrazole (85AG(E)56). The parent nitrilimine, HCNNH, has been generated by file photolysis of tetrazole (96LA1041). 

Recent studies of the chemistry of 2,5-disubstituted tetrazoles have been mainly concerned with reactions that involve loss of nitrogen and generation of nitrilimine intermediates. Examples of this have already been seen in the photolysis of these compounds and in the thermolysis of the unstable 2-acyltetrazoles obtained from acylation of 5-substituted tetrazoles. Direct thermolysis of 2,5-diaryltetrazoles141 142,442 also leads to nitrilimine intermediates [Eq. (39)]. These undergo a wide variety of... 

When treated with heat or light nitrogen, can be eliminated from tetrazoles and 1,2,3-triazoles. Nitrile imides can be formed by photolysis or thermolysis of 2,5-disubstituted tetrazoles. The nitrile imides can then react... 

Thermolysis of tetrazole oximes (478) in a suitable hydrocarbon solvent, or pyrolysis without it, produces 3,5-disubstituted 1,2,4-oxadiazoles (480) (Scheme 75) (81BSB193 87BSB675 91MIP137367). in the case of 5-unsubstituted tetrazoles (478 R = H), the reaction goes by two concomitant pathways, which imply elimination of hydrazoic acid or nitrogen. 

Gas-phase thermolysis of substituted tetrazoles (46a,b and 48), the 1,4-disubstituted 1,4-dihydro-5//-tetrazol-5-oncs (49a-f) and the 1,4-disubstituted 1,4-dihydro-5/7-tetrazol-5-thiones (50b,c,e-h) have been monitored by photoelectron spectroscopy.27... 

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