Gold‐Catalyzed Ring Expansion of Alkynyl Heterocycles through 1,2‐Migration of an Endocyclic Carbon–Heteroatom Bond

A mild and efficient gold‐catalyzed oxidative ring‐expansion of a series of alkynyl heterocycles using pyridine‐ N ‐oxide as the oxidant has been developed, which affords highly valuable six‐ or seven‐membered heterocycles with wide functional group toleration. The reaction consists of a regioselective oxidation and a chemoselective migration of an endocyclic carbon–heteroatom bond (favored over CH migration) with the order of migratory aptitude for carbon–heteroatom bonds being CS>CN>CO. In the absence of an oxidant, polycyclic products are readily constructed through a ring‐expansion/Nazarov cyclization reaction sequence.