Synthesis of 5-Substituted 1,3-Dimethylpyrazolo[4,3-e][1,2,4]triazines

A novel method for the synthesis of a new series of 5-substituted 1,3-dimethyl pyrazolo[4,3-e][1,2,4]triazines is described. The new synthetic strategy is based on the classical Bischler 1,2,4-benzotriazine synthesis. This approach involves the preparation of 5-hydrazinopyrazole from 5-chloro-1,3-dimethyl-4-nitropyrazole followed by acylation and nitro group reduction to form the corresponding 4-amino-3-(acylhydrazino)pyrazoles. Intramolecular oxidative cyclization of the latter derivatives, using polyphosphoric acid, produced the respective target pyrazolotriazines.