BICYCLIC [B]-HETEROANNULATED PYRIDAZINE DERIVATIVES .3. PARTIALLY HYDROGENATED TRIAZOLO[4,3-B]PYRIDAZINES

The structures of enyl-3-trifluoromethyl-s-triazolo[4,3-b]pyridazine ( 1), and its isomer, -trifluoromethyl-s-triazolo[4,3-b]pyridazin-6-one, (2), C19H15F3-N4O, have been solved. The two molecules differ in the bonding at N5 and in the conformation of the pyridazine ring which con tains this atom. This partially hydrogenated six-membered ring is puck ered in both molecules, adopting a half-chair shape in (1) and a twist -boat shape in (2). In both molecules, the triazole ring and the mean plane of the pyridazine ring are not coplanar.