Synthesis of pyrazolo[3,2-c]-1,2,4-triazines from N-(5-pyrazolyl)-α-ketohydrazidoyl halides

3-Phenylpyrazole-5-diazonium chloride (5) couples with benzenesulfonylacetone (9a) , benzenesulfonylacetophenone (9b) , ethyl benzenesulfonylacetate 9c , and ethyl benzoylacetate (12b) in ethanol in the presence of sodium acetate at room temperature to afford the pyrazolo3,2-c]-1,2,4-triazine derivatives 11a and 11b and the acyclic hydrazones 10c and 13 respectively. The products 11a,b and 10c can also be obtained from the reaction of the corresponding hydrazidoyl halides 8a-c with sodium benzenesulfinate in high yield. The hydrazones 10c and 13 can be cyclised thermally or under the influence of acid into pyrazolo3,2-c]-1,2,4-triazine derivatives 11c and 14 respectively.