Novel synthesis modes and properties of [1,4]benzodioxinopyridazines

A simple synthesis involving fusion of catechol and derivatives with 3,4,5-trichloropyridazine has furnished 4-chloro[1,4]benzodioxino[2,3-c]pyridazines 5 for the first time. This new method complements the previously reported base promoted procedure for preparing 4-chloro[1,4]benzodioxino[2,3-d]pyridazines 3. Employing both methods, 4-(trifluoromethyl)catechol was converted to the four regio isomers 3b,c and 5c,d. Reaction of methoxide with either 3 or 5, gave chlorine substitution with formation of methoxybenzodioxinopyridazines 6 and 7 respectively. However, these reactions both give what appears to be an unprecedented rearrangement, with conversion of [2,3-c]pyridazine to [2,3-d]pyridazine and vice versa