Sodium alginate: A biopolymeric catalyst for the synthesis of novel and known polysubstituted pyrano[3,2-c]chromenes.

A library of known and new 4-aroyl-pyrano[3,2-c]chromenes have been synthesized through the one-pot, three-component reaction of 4-hydroxycoumarin, aryl glyoxals, and malononitrile or ethyl cyanoacetate in the presence of sodium alginate without any post modification, as a biopolymeric bifunctional organocatalyst, in EtOH under reflux conditions in short times. The desired products were obtained in high to excellent yields under optimized conditions. This procedure offers many advantages, such as operational simplicity, a green solvent system, short reaction times, high to excellent yields, simple work up and separation, and using a natural commercially available polysaccharide that is transition-metal-free, biodegradable and recoverable. Furthermore, sodium alginate can be recycled at least four times with negligible loss of its catalytic activity.