Synthesis of fluorinated indazoles through ANRORC-like rearrangement of 1,2,4-oxadiazoles with hydrazine

A series of 6-substituted fluorinated indazoles has been obtained through an ANRORC-like rearrangement (Addition ofNucleophile, Ring-Opening and Ring-Closure) of 5-tetrafluorophenyl-1,2,4-oxadiazoles with hydrazine. The initial addition of the bidentatenucleophile to the electrophilic C(5) of the 1,2,4-oxadiazole ring, followed by ring opening and ring closure, leads to the formation offluorinated indazoles in high yield under mild experimental conditions. Functionalization of the C(6) in the final indazole nucleus waspreliminarily achieved through a nucleophilic aromatic substitution on the starting 5-pentafluorophenyl-1,2,4-oxadiazole.