A series of 12 silica gel-bound enaminones and their Cu(II) complexes were prepared and tested for their suitability as heterogeneous catalysts in azomethine imine-alkyne cycloadditions (CuAIAC). ...Immobilized Cu(II)–enaminone complexes showed promising catalytic activity in the CuAIAC reaction, but these new catalysts suffered from poor reusability. This was not due to the decoordination of copper ions, as the use of enaminone ligands with additional complexation sites resulted in negligible improvement. On the other hand, reusability was improved by the use of 4-aminobenzoic acid linker, attached to 3-aminopropyl silica gel via an amide bond to the enaminone over the more hydrolytically stable N-arylenamine C-N bond. The study showed that silica gel-bound Cu(II)–enaminone complexes are readily available and suitable heterogeneous catalysts for the synthesis of 6,7-dihydro-1H,5H-pyrazolo1,2-apyrazoles.
Pyrazoles and their reduced form, pyrazolines, are considered privileged scaffolds in medicinal chemistry, owing to their noteworthy biological activities, physicochemical properties and occurrence ...in many low-molecular-weight compounds present in several marketed drugs (e.g., Celebrex® and Viagra®). Pyrazoles are also found in a variety of agrochemicals (fungicides, insecticides, and herbicides) and are versatile compounds for synthetic manipulations. Their challenging chemical structures and properties (mainly tautomerism, with possible implications in their reactivity), and diverse applications, have attracted the attention of many researchers who have developed various synthetic approaches. This reprint presents some examples of the most recent advances in pyrazoles’ chemistry, including synthetic methodologies to access novel pyrazole derivatives, to their functionalization, and studies of their properties and applications in different fields, mainly in medicine and materials science.
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