Indazole moiety is a privileged N-heterocyclic structure in medicinal chemistry due to its pronounced biological and therapeutic activities,and especially,tricyclic 1H-benzo-indazole plays increasingly important role in drug discovery.1 In the past few decades,a number of impressive methods have been reported for the construction of indazole frameworks,2 yet synthetic protocols to benzo[f]indazole are severely scarce,which have hampered their biomedical applications.In our work,a novel and efficient strategy for the direct synthesis of benzo[f]indazoles via copper-catalyzed cascade reaction of sulfonyl hydrazides with 1,3-enynes under mild conditions has been developed.This method achieves the formation of two C–N bonds and one C–C bond in one pot,providing a series of benzo[f]indazoles in good yields with good functional group tolerance and remarkable regioselectivity.