The first practical approach to new pyrimido[4,5-d]pyridazines: novel chemoselective and regioselective reactions

Abstract

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.