Synthesis and rearrangement of 3-Amino-2-Benzyl[1,2,4]Triazolo[4,3-a]Pyrimidinium Salts

It has previously been shown that the reaction of 1-phenyl[1,2,4]triazole-3,5-diamine perchlorate with 1,3-diketones or 1,1,3,3-tetraethoxypropane yields 2-amino-1-phenyl[1,2,4]triazolo[1,5-a]pyrimidinium perchlorates [1]. According to the authors [1], these compounds are the products of a Dimroth rearrangement of the initially formed [4,3-a]-isomers, which could not be separated. We have shown that brief heating of 1-benzyl[1,2,4]triazole-3,5-diamine (1) with the 1,3-diketones 2a,b or 1,1,3,3-tetramethoxypropane (2c) in ethanol in the presence of HCl gives the 2-R-3-amino[1,2,4]triazolo[4,3-a]pyrimidinium chlorides 3a-c, i.e. condensation proceeds similarly to the reaction of 1-substituted [1,2,4]triazole-3,5-diamines with -ketoesters [2].