Room temperature aqueous Paal-Knorr pyrrole synthesis catalyzed by aluminum tris(dodecyl sulfate)trihydrate

This article reports a novel procedure to prepare pyrroles using a modification of the Paal-Knorr reaction. Water is a safe solvent meeting environmental considerations, but most organic substrates are not soluble in water. A possible solution to improve the solubility of substrates is the use of surface-active reagents that can form micelles. For instance, combined Lewis acid-surfactant catalyst acts both as a Lewis acid to activate the substrate molecules and as a surfactant to form emulsions in water. Here, we prepared and used aluminum tris(dodecyl sulfate)trihydrate to condense various amines to 2,5-hexadione at room temperature. The sole solid pyrrole was separated by a simple filtration. Our findings thus show a novel and improved modification of the Paal-Knorr reaction in terms of mild reaction conditions and clean reaction profiles, using a simple workup procedure and improved yields with excellent chemo-selectivity.