Bi(OTf)3-catalyzed solvent-free synthesis of pyrano[3,2-c]coumarins through a tandem addition/annulation reaction between chalcones and 4-hydroxycoumarins

A Bi(OTf)3-catalyzed tandem addition/annulation reaction is described in order to synthesize pyrano[3,2-c]coumarins under solvent-free conditions. Substituted/unsubstituted chalcones were conveniently condensed with various 4-hydroxycoumarins by means of this environmentally benign method which produces water as the only side product.