Direct Synthesis of Benzo[ f]indazoles from Sulfonyl Hydrazines and 1,3-Enynes by Copper-Catalyzed Annulation.

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 moderate to good yields with good functional group tolerance and remarkable regioselectivity.