“…3,4-Dihydropyrano[c] chromene derivatives are generally synthesized via one-pot reaction of an aryl aldehydes, malononitrile and 4-hydroxycoumarin in the presence of several catalysts such as sodium dodecyl sulfate (SDS) 14 , DBU 15 , morpholine 16 , piperidine 17 , K 2 CO 3 under microwave irradiation 18 , sulfonic acid functionalized silica (SiO 2 PrSO 3 H) 19 , trisodium citrate 20 , silica gel 21 , inorganic-organic hybrid magnetic nanocatalyst 22 28 and heteropoly acids 29 . However, in spite of their potential utility, some difficulties still exist, such as expensive or toxic reagent.…”