Pyridazine derivatives and related compounds, Part 17: The synthesis of some 3-substituted pyridazino{[}3 `, 4 `: 3,4]pyrazolo {[}5,1-c]-1,2,4-triazines and their antimicrobial activity

The reaction of the hydrazide of pyridazino{[}3',4':3,4]pyrazolo{[}5,1-c]-1,2,4-triazine-3-carboxylic acid 3 with carbon disulfide in the presence of potassium hydroxide gave the 1,3,4-oxadiazole-2-thione derivative 4. The methylation of this product in an alkaline medium proceeds at the sulfur atom. The reaction of 3 with KOH and carbon disulfide followed by addition of hydrazine hydrate afforded the 4-amino-1,2,4-triazole derivative 6. Compound 3, when heated either with ammonium thiocyanate or with potassium thiocyanate, afforded the same product 7, which underwent cyclodehydration in the presence of acetyl chloride, which led to the 2-acetylamino-1,3,4-thiadiazole derivative 8. In a basic medium, the product was 1,2,4-triazole-3-thione derivative 9. The reaction of 3 with phenyl isothiocyanate provided thiosemicarbazide derivative 10, which underwent cyclodehydration in a basic medium and gave the 1,2,4-triazole derivative 11. The reaction of 3 with formic acid yielded the 3-carboxyl-2'-(formyl)hydrazine derivative 12. The refluxing of the latter with phosphorus pentasulfide in xylene yielded compound 14 (65\%). The reaction of compound 12 with phosphorus pentoxide afforded compound 15. Some representative examples were screened for antimicrobial activity.