Transition-Metal-Free Ring Expansion Reactions of Indene-1,3-dione: Synthesis of Functionalized Benzoannulated Seven-Membered Ring Compounds.

A novel ring expansion reaction of indene-1,3-dione with alkynyl ketones under transition-metal-free conditions has been developed. This process offers an efficient and direct way to synthesize benzoannulated seven-membered rings or fused-ring compounds through C-C σ-bond activation. Notable features of the procedure include easily accessible starting materials, good functional group tolerance, and high atom economy.