Direct synthesis of fluorene-based spirolactones through a BF3-promoted spiroannulation of α-keto acids and o-alkynylbiaryls

A novel and practical approach to fluorene-based spirolactones has been described via BF 3 -promoted spiroannulation of α-keto acids and o -alkynyl biaryls. This metal-free cascade reaction provides a wide range of products in good to excellent yields.