Ynone-triggered ring expansion of indandiones: transition-metal-free access to benzoannulated seven-membered rings.

A transition-metal-free ring expansion of 2-(2'-ketoalkyl)-1,3-indandiones with ynones provides access to benzotropones and cyclohepta-fused furans under mild basic conditions. The transformation proceeds through a ynone-triggered annulation followed by cyclization and dehydration, generating a key intermediate that undergoes retro-Claisen-type C-C bond cleavage to furnish structurally complex fused furan-tropone frameworks. The method exhibits broad substrate scope and good functional-group tolerance, including heteroaryl and aliphatic ynone partners, and its synthetic utility is demonstrated by gram-scale synthesis and diverse product derivatizations.