A convenient method for the synthesis of dihydropyranobenzopyrandiones and their sulfur analogs

Abstract

A general and convenient synthesis is described of a number of 2,3-dihydro-4H,5H-pyrano[3,2-c][1]benzopyran-4,5-diones and 2,3-dihydro-4H,5H-pyrano[2,3-b][1]benzothiopyran-4,5-diones. It involves the condensation of 4-hydroxycoumarin derivatives and their thioanalogs with different α,β-unsaturated acids in the presence of PPA. Assignments of the structures in both the cases are based on analytical and spectroscopic evidence.