Abstract Dehydrogenation and amination of 4, 4a, 5, 6-tetrahydro and 5, 6- dihydrobenzocinnolinones in refluxing hydrazine hydrate to give new benzo [h] cinnolinones and 4-aminobenzo [h] cinnolinones are reported, and reaction mechanisms proposed. Experiments were also extended to 4, 4a-dihydro-5H-indenopyridazinone which underwent hydrazine induced dehydrogenation to 5H-indenopyridazin-3-one but not subsequent ...