Copper-Catalyzed Sequential Cyclization/Migration of Alkynyl Hydrazides for Construction of Ring-Expanded N–N Fused Pyrazolones

A copper-catalyzed sequential cyclization/migration reaction of alkynyl hydrazides for the synthesis of ring-expanded N–N fused pyrazolones was developed. Control experiments indicate that the copper–ligand complex plays an essential role in the reaction. This approach features a broad scope including some functional group tolerance as well as a nucleophilic addition/1,3-migration/formal 1,2-migration sequence. This protocol provides simple manipulation and less waste due to high yield and atom economy. The synthetic utility of N–N fused pyrazolones was also demonstrated by further transformations.