Synthesis of tetrahydropyridazino[1,2‐ a ][1,2,4] benzotriazin‐6‐one derivatives. A novel heterocyclic system

Synthesis of pyridazino[1,2‐ a ][1,2,4]benzotriazin‐6‐one derivatives involving reaction of either 1,2,3,6‐tetra‐hydropyridazine ( 9 ) or hexahydropyridazine 14 with 2‐fluoro‐5‐nitrophenylisocyanate ( 5 ) to give, via intramolecular cyclization, 3a and 16 respectively is described. Compound 3a was converted to 18 via methylation and hydroxylation to give 20 followed by conversion to the acetonide derivative 18 . Both 16 and 18 were reduced to the amino derivatives 17 and 19 respectively.