Microwave‐promoted Synthesis of Novel Fused Osthole Analogues

Osthole is a natural coumarin derivative and has a broad scope of biological activities. Two series of novel fused osthole analogues were designed, and synthesized through a highly efficient microwave‐promoted synthetic protocol via the reaction of 4‐hydroxycoumarins and β‐ketoesters. The reaction conditions including solvent, catalyst, microwave power and irradiation time were also optimized. The pyrano[3,2‐c]chromene‐2,5‐diones and furo[3,2‐c]coumarins were obtained through two distinct intramolecular cyclization processes, and the proposed mechanism was also discussed.