Abstract: 3-Aryl hydrazono-6-methyl-α,γ-pyronone is an important intermediate for the synthesis of a series of dihydro-pyridazones.This intermediate was separated and purified for the first time.By X-ray diffraction method,its crystalline structure was elucidated.NMR monitoring technique was applied to investigate the following ring-closure reaction under acidic and basic conditions.It was proposed that there underwent a mechanism as first by a lactone ring-opening then followed by a dehydrating cyclization reaction.

Key words: Pyronone, Pyridazone, Catalytic ring-closure, NMR monitoring