DBU: a highly efficient catalyst for one-pot synthesis of substituted 3,4-dihydropyrano[3,2-c]chromenes, dihydropyrano[4,3-b]pyranes, 2-amino-4H-benzo[h]chromenes and 2-amino-4H benzo[g]chromenes in aqueous medium

We have reported DBU catalyzed one-pot synthesis of 3,4-dihydropyrano3,2-c]chromenes, dihydropyrano4,3-b]pyranes, 2-amino-4H-benzoh]chromenes and 2-amino-4H-benzog]chromenes from aldehydes, active methylene compounds malononitrile/ethyl cyanocacetate, and 4-hydroxycoumarin/4-hydroxy-6-methylpyrone/1-naphthol/2-hydroxynaphthalene-1,4-dione in water under reflux. The attractive features of this process are mild reaction conditions, reusability of the reaction media, short reaction times, easy isolation of products, and excellent yields.