Green synthesis of 3-(1-naphthyl), 4-methyl-3-(1-naphthyl) coumarins and 3-phenylcoumarins using dual-frequency ultrasonication

Green synthesis of 3-(1-naphthyl), 4-methyl-3-(1-naphthyl) coumarins and 3-phenylcoumarins has been carried out in one step by reacting 2-hydroxybenzaldehydes and 2-hydroxyacetophenones with 1-naphthylacetic anhydride and phenylacetic anhydride, respectively, using dual-frequency ultrasonication, i.e. ultrasonic bath of 40 kHz and probe of 20 kHz. The compounds were obtained in very high yield (80–90%) and their structures were confirmed by infrared and nuclear magnetic resonance data