Indium-Catalyzed [1 + <i>n</i>] Annulation Reaction between β-Ketoester and α,ω-Diyne

A catalytic amount of In(NTf2)3 effects the inter- and intramolecular addition of a β-ketoester to an α,ω-diyne to produce a 1,3-dimethylenecycloalkane derivative in a single step. This [1 + n] annulation reaction shows good functional group tolerance and allows the synthesis of five- to seven-membered carbo- and heterocyclic as well as spirocyclic structures in moderate to excellent yields.