Efficient Microwave Solvent-Free Synthesis of Flavones, Chromones, Coumarins and Dihydrocoumarins

Simple, clean, environmentally friendly procedures for the solvent-free preparation of coumarins, dihydrocoumarins, flavones and chromones under microwave heating are described. Silica-supported Wells-Dawson heteropolyacid (H6P2W18O62 center dot 24 H2O) was employed as catalyst. High selectivity, very good yields and short reaction times were obtained. The results are compared with those of the reactions performed under conventional heating.