Abstract
Irradiation of 6-unsubstituted-2-methyl-3 (2H)-pyridazinone 1-oxide (5) in neutral alcohol resulted in the ring contraction to form N-methylamino-isomaleimide (6), γ-lactone of 4-hydroxy-2-pentenoic acid (7), 2-methyl-3, 6-pyridazinedione (8), and the deoxygenated parent pyridazinone (9). The 6-substituted 1-oxide (5) afforded 7 and 9 alone. On the other hand, in the case of irradiation in alcohol containing HCI, the 6-unsubstituted compound (5) afforded 6-chloro-2-methyl-3 (2H)-pyridazinone (14), derived by chlorination at the α-position to the N-oxide group. The 6-substituted compound (5) gave 6-chloromethyl-3 (2H)-pyridazinone (15), derived by chlorination at N-CH3 group. The formation mechanism of these compounds is also discussed.
