One‐pot Method for Reduction of Pyrazolo[5,1‐c][1,2,4]Triazine‐7‐diazonium Tetrafluoroborate to 7‐Hydrazinyl Derivatives

New convenient one‐pot method for reduction of hetarenediazonim tetrafluoroborates to the hetarylhydrazine derivatives was developed. Interaction of 8‐carboxyethyl‐3‐(tert‐butyl)‐4‐oxo‐4,6‐dihydropyrazolo5,1‐c ]1,2,4]triazine‐7‐diazonium tetrafluoroborate with anhydrous SnCl₂ in anhydrous CF₃CO₂H, and further sequence of one‐pot operations led to formation of various derivatives of the unstable ethyl 3‐(tert‐butyl)‐7‐hydrazinyl‐4‐oxo‐4,6‐dihydropyrazolo5,1‐c ]1,2,4]triazine‐8‐carboxylate (hydrochloride, hydrazides, hydrazones, and pyrazoles), which were isolated in high yields. The anhydrous conditions were first used with SnCl₂ and allowed to exclude hydrolysis of the ester group and formation of the by‐products.