The reactions of substituted 2-alkyl-2H-tetrazol-5-ylhydrazones with bromine and lead tetra-acetate: routes to 6-aryl-1-methyl[1,2,4]triazolo[4,3-d]tetrazoles

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Abstract
2-Methyl-2H-tetrazol-5-ylhydrazones were generally more reactive towards electrophilic reagents than the 1-methyl isomers and their reactions involved considerable amounts of decomposition. When treated with bromine the hydrazones yielded hydrazidic bromides. These latter materials were much less reactive than the 1-methyl isomers and were solvolysed ca. 200 times more slowly in dioxan–water (90% v/v). The products of the solvolysis were new triazolotetrazoles. This reaction, which probably involved the formation of an azocarbonium ion intermediate which underwent nucleophilic ring closure with the tetrazole ring as nucleophile, was in competition with nucleophilic attack by solvent water, and was eliminated when a highly nucleophilic solvent such as aniline was used. When the tetrazolylhydrazones were treated with lead tetra-acetate, cyclisation to the triazolotetrazoles constituted only a minor reaction. The major reaction involved here was an acetoxylation of the hydrazone, to give an N-acetyl hydrazide. Deacetylation of these N-acetyl hydrazides afforded a convenient conversion of the parent hydrazones into hydrazides.

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