Aqua one-pot, three-component synthesis of dihydropyrano[3,2-c]chromenes and amino-benzochromenes catalyzed by sodium malonate

The widespread biological properties of dihydropyrano[3,2-c]chromenes, 2-amino-4-aryl-4H-benzo[h]chromenes, and 3-amino-1-aryl-1H-benzo[f]chromenes have led to increasing efforts for the development of tremendously effective synthetic protocols aimed at their synthesis. In this contribution, sodium malonate was employed for the first time as an efficient catalyst for the one-pot, three-component tandem Knoevenagel-cyclocondensation reaction of 4-hydroxycoumarin (or naphthols), malononitrile/ethyl cyanoacetate, and various aldehydes. These compounds underwent Knoevenagel-Michael-Thorpe-Ziegler cyclization upon heating at 70 A degrees C in water to give the respective medicinally relevant dihydropyrano[3,2-c]chromenes and amino-benzochromenes. The method is versatile and amenable to many substrates as it requires no specialized devices such as microwave, ultrasound and ball-milling. Also, the salient features of this high-yielding protocol are green reaction conditions, the use of commercially available catalyst, easy purification processes by a simple filtration, and relatively shorter reaction times.