1) The cyclization of 6-chloro-3-hydrazino-4-methylpyridazine (I) with refluxing formic acid gives 6-chloro-8-methyl-1,2,4-triazolo[4,3-b]pyridazine (II), which is then condensed with piperidine (III) at reflux temperature.
2) By cyclization of 3-hydrazino-4-methyl-6-piperidinopyridazine (I) in refluxing formic acid.