A solvent-free synthesis of coumarins using a Wells-Dawson heteropolyacid as catalyst

Substituted coumarins are synthesized from phenols and beta-ketoesters by the Pechmann reaction, using a Wells-Dawson heteropolyacid (H(6)P(2)W(18)O(62)(.)24H(2)O) as catalyst by a solvent-free procedure. This one requires low reaction times, 130degreesC temperature and as little as 1 mol% of Wells-Dawson acid, obtaining good to excellent yields of coumarins. The catalyst showed to be reusable with no differences in the yields. The results are compared with those of the reactions performed in toluene solution. The presented synthetic procedure is a convenient, clean and fast alternative for synthesizing 4-substituted coumarins (17 examples). (C) 2004 Elsevier Ltd. All rights reserved.