The oxidation of s-triazolo[4,3-b]pyridazines with selenium dioxide

Some s-triazolo[4,3-b]pyridazines were oxidized to 2,3-dihydro-s-triazolo[4,3-b]pyridazin-3-ones with selenium dioxide in nitrobenzene at 160–165° (external temperature) for 1–2 hours in 30–40% yields.