Solvent Free Three-Component Synthesis of 2,4,5-trisubstituted-1-pyrrol-3-ol-type Compounds from -tryptophan: DFT-B3LYP Calculations for the Reaction Mechanism and 3-pyrrol-3-one↔1-pyrrol-3-ol Tautomeric Equilibrium.

In this paper, we describe the solvent-free three-component synthesis of 2,4,5-trisubstituted-1-pyrrol-3-ol-type compounds from -tryptophan. The first step of the synthetic methodology involved the esterification of -tryptophan in excellent yields (93-98%). Equimolar mixtures of alkyl 2-aminoesters, 1,3-dicarbonyl compounds, and potassium hydroxide (0.1 eq.) were heated under solvent-free conditions. The title compounds were obtained in moderate to good yields (45%-81%). Density functional theory using "Becke, 3-parameter, Lee-Yang-Parr" correlational functional (DFT-B3LYP) calculations were performed to understand the molecular stability of the synthesized compounds and the tautomeric equilibrium from 3-pyrrol-3-one type intermediates to 1-pyrrol-3-ol type aromatized rings.