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12-Tungstophosphoric acid (PW) supported on different metal oxides (SiO 2 , γ-Al 2 O 3 , KSF, K10) and activated carbon were prepared by impregnation method and their catalytic performances were evaluated in three component condensation of benzaldehyde, ethyl acetoacetate and ammonium acetate to afford corresponding 1,4-dihydropyridine. A high catalytic activity was found over silica supported PW. Effect of PW loading, catalyst loading and solvent was studied to introduce the best reaction condition. Based on the above experimental finding, catalytic performances was optimized with a loading of 40% PW onto SiO 2 (0.2 g) under solvent-free condition. The characterization data derived from FT-IR, XRD, and TGA–DSC techniques reveal that the PW on silica support exists in Keggin structure. In addition, acidity measurements were performed by potentiometric titration with n -butylamine. The activity of the catalysts is strongly dependent on their acidic characteristic which, in turn, depended on PW loading. Finally, a series of 4-aryl, N -alkyl, and N -aryl substituted 1,4-dihydropyridines have been synthesized in high to excellent yield in short reaction times. PW/SiO 2 was found to be reusable and a considerable catalytic activity still could be achieved after fourth run.

The multicomponent Strecker reaction using trimethylsilyle cyanide was performed in very short reaction times, and α-aminonitriles were prepared in excellent yields in the presence of a catalytic amount of alumina-supported tungstosilicic acid.

The production of β-acetamido ketones from aldehydes, ketones and acetyl chloride in acetonitrile over supported heteropoly acids has been examined. This study reports the use of heteropoly acids (HPAs) supported on metal oxides (SiO2, Al2O3, K 10 and KSF montmorillonite) and activated carbon as efficient and reusable catalysts, and their comparison with other catalysts in Dakin–West reaction. Dodecatungstophosphoric acid supported on KSF and γ-Al2O3 shows the best results and reusability.

The multicomponent Strecker reaction using trimethylsilyle cyanide or potassium cyanide was performed in very short reaction times and α-aminonitriles were prepared in excellent yields in the presence of a catalytic amount of silica supported dodecatungstophosphoric acid. The simple experimental and product isolation procedure combined with easy recovery and reusability of the catalyst are expected to contribute to the development of clean and environmentally friendly strategy for the synthesis of α-aminonitriles.

In the presence of KSF-supported heteropoly acid as a heterogeneous, reusable and inexpensive catalyst, three-component reactions between aldehydes or ketones, amines, and trimethylsilyl cyanide preceded to afford α-aminonitriles in excellent yields, very short reaction times, and low loading of catalyst. This catalyst was highly selective and other functional groups including carbon-carbon double bond, and heterocyclic moieties did not affect the reaction. KEY WORDS : Heterogeneous catalysis, Clays, Combinatorial chemistry, α-Aminonitrile, Heteropoly acid Bull. Chem. Soc. Ethiop. 2010 , 24(2), 209-215.

The multicomponent Strecker reaction using trimethylsilyle cyanide was performed in very short reaction times, and α-aminonitriles were prepared in excellent yields in the presence of a catalytic amount of alumina-supported tungstosilicic acid.

Catalytic performance of different supported heteropoly acids (HPAs) in the synthesis of β-enaminones and β-enamino esters from various substituted amines and β-diketones or β-keto esters has been studied. In order to improve the yield and reaction time, the effect of various solvents, HPA loading, different amount of the catalyst and solventless conditions have been investigated. 40% (w/w) PW/SiO2 was found to be a very efficient and reusable catalyst in comparison with others, under solvent free conditions. In this eco-friendly approach, the usage of organic solvents and hazardous reagents were minimized. Also, a high yield of products within short reaction times were obtained.

Catalytic performance of different supported heteropoly acids (HPAs) in the synthesis of β-enaminones and β-enamino esters from various substituted amines and β-diketones or β-keto esters has been studied. In order to improve the yield and reaction time, the effect of various solvents, HPA loading, different amount of the catalyst and solventless conditions have been investigated. 40% (w/w) PW/SiO2 was found to be a very efficient and reusable catalyst in comparison with others, under solvent free conditions. In this eco-friendly approach, the usage of organic solvents and hazardous reagents were minimized. Also, a high yield of products within short reaction times were obtained.

Tungstophosphoric acid supported on titania (PW/TiO 2 ), catalyzed three and four component coupling of various β-dicarbonyl compounds, aldehydes and amines under solvent free conditions. Different 4-aryl, N-hydroxy ethyl and N-aryl substituted 1, 4-dihydropyridines and polyhydroquinoline derivatives, have been synthesized with high to excellent yields. Short reaction times, simple work-up, and mild reaction conditions are advantages of this procedure. The catalyst is reusable without loss of activity for five runs.