1,2,3 triazole iminium intermediate

The authors supported the reaction with a possible mechanism via an iminium intermediate (Scheme 4.40). In the first step, the a,p-unsaturated ketone 102a reacts with the catalyst piperidine 103 to generate the iminium intermediate A. Cycloaddition between the iminium species A and the azide 15 generated the triazoline intermediate B, which on hydrolysis of the iminium center and subsequent air oxidation of the triazoline moiety in C resulted in the formation of the fully substituted triazole 104e. 

Scheme 4.40 Mechanism of 1,2,3-triazole formation via iminium intermediate.

Another field of research is concerned with the one-pot synthesis of this system from readily available starting materials. In Scheme 12, reaction of phenyl azide and malononitrile in the presence of sodium ethoxide leads, via the intermediate triazole (139), to the self-condensation product (140), itself a triazolopyrimidine. In the presence of other nitriles the preferred formation of the more useful compounds (141) occurs in low to moderate yields with small amounts of dimer <87JHC997>. Direct synthesis of the 5,7-dione derivatives (143) (60-90%) is achieved by the reaction of the readily available aminopyrimidinedione (142) with an azide iminium salt in dichloromethane at moderately high dilution <87JHC1493>. 

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