Sodium alginate: An efficient biopolymeric catalyst for green synthesis of 2-amino-4H-pyran derivatives

Abstract

Sodium alginate, a naturally occurring macromolecule, in its granular form and without any post-modification was found to be an efficient and recoverable bifunctional heterogeneous organocatalyst for the domino synthesis of various 2-amino-3-cyano-4H-pyran annulated derivatives through three-component condensation of different aldehydes, malononitrile and diverse 1,3-dicarbonyl compounds under mild conditions. Corresponding 4H-pyran derivatives were obtained in high to excellent yields after 25-150min stirring in 2mL EtOH under reflux conditions in the presence of 10mol% of sodium alginate, equimolar amounts of aldehydes, malononitrile and 1,3-dicarbonyl compounds. The catalyst was easily separated from the reaction mixture to obtain desired products in excellent purity as shown by FTIR and (1)H NMR spectroscopic methods. Avoiding the use of any transition metal, one-pot and multi-component procedure catalyzed by a renewable biopolymer, the reusability of the catalyst, broad substrate scope and operational simplicity are important features of this methodology for preparation of medicinally important compounds.

Keywords: 4H-Pyrans; Bifunctional organocatalyst; Biopolymers; Green chemistry; Sodium alginate.