Facile route to highly functionalized 2H-chromene-2-thiones via ring annulations of β-oxodithioesters with phenols catalyzed by AlCl3 under solvent-free conditions

A facile synthesis of chromene-2-thiones by the Pechmann condensation of phenols and β-oxodithioesters catalyzed by AlCl3 under solvent-free condition has been reported. The best results were obtained in the case of substituted phenols such as resorcinol, substituted resorcinol, and pyrogallol. The optimum condition was observed with the use of 10 mol % of AlCl3 at 130 °C under solvent-free conditions. This method offers a wide scope for the synthesis of coumarins in good yields during a short period of time.