Microwave-induced calcium(II) chloride-catalyzed Paal–Knorr pyrrole synthesis: a safe, expeditious, and sustainable protocol

Green Synthesis of Bioactive Pyrrole Derivatives via Heterogeneous Catalysts Since 2010

Pyrrole derivatives are known as building blocks for the synthesis of biological compounds and pharmaceutical drugs. Several processes were employed to synthesize pyrroles, including Hantzsch, Paal-Knorr, and cycloaddition of dicarbonyl compounds reaction. Using catalysts like nanoparticles, metal salts, and heterogeneous ones was necessary to obtain the targeted pyrrole structure. Also, to afford more active pyrrole compounds, heterocyclic molecules such as imidazole or other rings were used in the synthesis as amines. This review presents heterogeneous catalysts since 2010 for the green synthesis of bioactive pyrroles in a one-pot multi-component reaction. Additionally, each synthetic method included a demonstration of the suggested mechanisms. Diakylacetylenedicarboxylate, dicarbonyl group, amines, furans, and acetylene group are consolidated to yield biological pyrroles through the heterogeneous catalysts. Finally, various pyrrole-performed activities were displayed, such as antibacterial, anti-inflammatory, analgesic, and other significant activities.

Crystallographic, spectroscopic and thermal studies of 1-(4-bromophenyl)-5-(2,5-dimethyl-1H-pyrrol-1-yl)-3-methyl-1H-pyrazole

The new title pyrrole-pyrazole derivative, C16H16BrN3, was synthesized through a citric acid-catalyzed Paal-Knorr reaction between acetonylacetone and 1-(4-bromophenyl)-3-methyl-1H-pyrazol-5-amine under mild reaction conditions. This synthetic protocol is noteworthy for its utilization of stoichiometric amounts of the reactants, an ecofriendly solvent and a cost-effective, non-toxic and biodegradable organocatalyst. A comprehensive understanding of the molecular structure was gained through spectroscopic, thermal and X-ray crystallographic analyses. The crystal structure is characterized by weak interactions, where only C-H...π connections contribute to the hydrogen-bond contacts. The supramolecular assembly is controlled by dispersion forces. However, the energy frameworks demonstrate that these forces act in three dimensions, providing enough stability, as observed in TGA-DSC (thermogravimetric analysis-differential scanning calorimetry) studies.