Synthesis and photochemical reactivity of 3-methylisoxazolo[4,5-d]pyridazines

A synthetic pathway to 3-methylisoxazolo4,5-d]pyridazine and some of its derivatives is described. Uv irratiation of 4,7-dimethoxy (XVII) and 7-chloro-4-hydrazino-3-methylisoxazolo4,5-d]pyridazine (IX) shows that both intramolecular rearrangements and solvent involving reactions can occur.