Mechanochemical Synthesis of Indene-Containing Spirolactones via Tf2O-Promoted Cascade Cyclization of 2-Benzoylbenzoic Acids with Arylalkynes

The Tf2O-promoted cascade cyclization of 2-benzoylbenzoic acids with arylalkynes was achieved under solvent-free ball-milling conditions. This process renders rapid entry to the rare indene-containing spirolactones via intramolecular cyclization of 2-benzoylbenzoic acids and subsequent annulation with arylalkynes, which resulted in one C-O and two C-C bond formations. As the reactions utilize easily available starting materials and proceed in the absence of organic solvents, the present protocol constitutes an expedient and environmentally friendly access to indene-containing spirolactones.