Preparation of Pyrido[2,3-b]indole Derivatives Using Silicates of Group 1 and 2 Metals

An efficient synthesis of 2,4-diaryl-9H-pyrido[2,3-b] indole derivatives in aqueous medium via the three-component reaction of indolin-2-one, a chalcone and ammonium acetate was developed using Na₂SiO₃, K₂SiO₃, Li₂SiO₃, CaSiO₃, MgSiO₃, BaSiO₃, SrSiO₃, and ZnSiO₃ as catalysts. Results of activity evaluations indicated that among of the metal silicate used alkali metal silicates exhibits much higher activity than other samples due to the stronger basicity power and higher solubility in water. Under the optimum reaction conditions, all of the reactions with diverse aromatic aldehydes provided high yields in low reaction times.