When 4-Chloro-3-vinyl Coumarins Meet Cyclic 1,3-Diketones: Chemoselective and Unexpected Synthesis of Benzocoumarin Derivatives

A series of pyranocoumarins and benzocoumarins were synthesized by base-mediated reaction of 4-chloro-3-vinyl coumarins with cyclic 1,3-dikeones in ethanol at reflux. Reactions using dimedone and 1,3-cyclohexadione gave pyranocoumarins, whereas 1,3-indandione resulted in the formation of unexpected benzocoumarin derivatives. These transformations were carried out under relatively green and mild conditions, provided access to novel coumarin-based heterocycles in synthetically useful yields.