n → π* interactions stabilize the -ac isomers of arylhydrazides and facilitate their SAr autocyclizations.

We describe a novel mechanism of stabilization of the -ac isomer of an arylhydrazide n → π* interactions. We further show that when a leaving group (F) is present at the -position of the carbonyl group of such an arylhydrazide, the n → π* interaction facilitates an SAr autocyclization reaction to produce indazolone, an important heterocycle with biological activity. Faster autocyclization of arylhydrazide is observed when an electron withdrawing group is present in the aryl ring, which is a characteristic of SAr reactions.