Novel and efficient catalysts for the one-pot synthesis of 3,4-dihydropyrano[c]chromene derivatives in aqueous media

Diammonium hydrogen phosphate, (NH4)2HPO4(DAHP), efficiently catalyzes the one-pot, three-component reaction of an aromatic aldehyde, malononitrile and 4-hydroxycoumarin in aqueous media under mild conditions at room temperature, to afford the corresponding dihydropyrano[c]chromenes in high yields. (S)-Proline has also been used as another neutral catalyst for this reaction at reflux.