Tungstate sulfuric acid-catalyzed Knorr reaction have been used as a simple, rapid, atom economic and green method for the synthesis of indazole and pyrazole derivatives based on the condensation of hydrazine derivatives and b-dicarbonyl compounds under solvent-free conditions. It was found that the catalyst could be recovered and reused without significant loss of its activity. The use of this method provides a novel and improved modification of Knorr synthesis in terms of clean reaction profile, use of a safe catalyst and solvent-free conditions.

A new three-component condensation of aryl glyoxals, acetylacetone and urea in the presence of a small amounts of tungstate sulfuric acid (TSA) leads to novel functionalized 5-acetyl-4-(aryloyl)-3,4-dihydropyrimidinones which these heterocycles can undergo the Knorr condensation with hydrazines to produce new pyrimido [4,5-d]pyridazines in good yields. These approaches are consistent with principles of green chemistry due to some factors, such as the use of a safe and recyclable catalyst under solvent-free conditions.

A Modified and Practical Synthetic Route to Indazoles and Pyrazoles Using Tungstate Sulfuric Acid. -Indazole and pyrazole derivatives are obtained by the simple, rapid, and green tungstate sulfuric acid-catalyzed Knorr reaction of hydrazine derivatives with various -dicarbonyl compounds under solvent-free reaction conditions. The catalyst is reusable without significant loss of activity. -(RAHMATZADEH, S. S.; KARAMI*, B.; KHODABAKHSHI, S.; J. Chin. Chem. Soc. (Weinheim, Ger.) 62 (2015) 1, 17-20, http://dx.doi.org/10.1002/jccs.201400251 ; Dep. Chem., Yasouj Univ., Yasouj 75918, Iran; Eng.) -H. Toeppel 23-135