Silica-Bonded N-Propylpiperazine Sodium n-Propionate as Recyclable Basic Catalyst for Synthesis of 3,4-Dihydropyrano[c]chromene Derivatives and Biscoumarins

A simple and efficient procedure for the preparation of silica-bonded N-propylpiperazine sodium n-propionate (SBPPSP) by the hydrolysis of silica-bonded N-propylpiperazine methyl n-propionate (SBPPMP) in hydrochloric acid (0.5 mol/L) followed by treatment with saturated sodium bicarbonate is described. The SBPPMP was obtained by the reaction of 3-silica-bonded N-propylpiperazine and methyl acrylate in methanol. SBPPSP was used as a recyclable basic catalyst for the synthesis of 3,4-dihydropyrano[c]chromenes by the reaction of aromatic aldehydes, malononitrile, and 4-hydroxycoumarin in aqueous ethanol (1:1 v/v) under reflux conditions. Biscoumarins were also obtained via condensation of aldehydes and 4-hydroxycoumarin in aqueous ethanol (1:1 v/v) under reflux conditions. The catalyst could be recycled several times without any additional treatment.