Synthesis of Spiro[5.n (n=6-8)]heterocycles through Successive Ring-Expansion/Indole C-2 Functionalization

A cascade procedure for the efficient and atom-economical synthesis of spiro[5.n (n=6-8)]heterocycles has been developed. This process goes through the tandem reactions of base-promoted ring-expansion of cyclic ketones followed by Cu-catalyzed intramolecular C-2 spirocyclization of indoles. Easily accessible starting materials and broad substrate scope are the advantaged features of this protocol.