Regioselective synthesis of pyrano[3,2-c]coumarins via Cu(II)-catalyzed tandem reaction

Efficient synthesis of pyrano[3,2-c]coumarins has been achieved via copper(II) triflate catalyzed tandem reaction of 4-hydroxycoumarin with α,β-unsaturated carbonyl compounds in high yields. The catalytic reaction proceeded very smoothly under solvent-free conditions and showed high regioselectivity. The synthetic potential of this methodology was explored to 4-hydroxy-6-methyl-2-pyrone successfully.