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

We describe a novel mechanism of stabilization of the E -ac isomer of an arylhydrazide via n N → π* Ar interactions. We further show that when a leaving group (F) is present at the ortho -position of the carbonyl group of such an arylhydrazide, the n N → π* Ar interaction facilitates an S N Ar 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 S N Ar reactions. The n N → π* Ar interaction-mediated stabilization of the E -ac isomers of arylhydrazides and their S N Ar autocyclization to indazolones are discussed.