Role of various heteropolyacids in the reaction of 4-hydroxycoumarin, aldehydes and ethylcyanoacetate

The effects of various heteropolyacids including Preyssler, Wells-Dawson and Keggin regarding the yields and types of products in the reaction of 4-hydroxycoumarin, aldehydes and ethylcyanoacetate have been investigated. The results show that dihydropyrano[3,2-c]chromenes were obtained in the presence of Preyssler and Wells-Dawson as the only products while in the presence of Keggins, this reaction led to formation of two compounds including bis-coumarins as major and dihydropyrano[3,2-c]chromenes as minor products.