Agar–sulfuric acid catalyzed synthesis of tetrahydro-4H-chromene-3-carbonitrile derivatives

Tetrahydrobenzo[b]pyran, pyrano[2,3-d]pyrimidine, and pyrano[c]chromene derivatives have attracted much attention due to their wide range of biological properties [1].4H-pyrans and their derivatives have also attracted great attention due to their useful biological and pharmacological properties [2]. Furthermore, substituted 4H-pyrans also constitute a structural unit of a series of natural products [3]. On the other hand organic reactions under solvent‐free conditions have also attracted much interest from chemists particularly from the viewpoint of green chemistry. The possibility of performing multicomponent reactions under solvent‐free conditions using an environmentally friendly catalyst could enhance the efficiency from an economic as well as ecological point of view[4].In continuation of our efforts to develop new, green chemistry methods as well as our interest on applications of heterogeneous-catalyzed organic reactions,we decided to explore the possibility of synthesizing tetrahydro-4H-chromene-3-carbonitrilederivatives via a One- Pot , three-component condensation of dimedone, aromatic aldehydes and malononitrile under solvent-free conditions using agar–sulfuric acid [ASA] as a recyclable catalyst (figure 1).