Revisit to the synthesis of 1,2,3,4-tetrasubstituted pyrrole derivatives in lactic acid media as a green solvent and catalyst.

In this study, for the first time, lactic acid was used as a bio-based green catalyst and reaction medium for the synthesis of 1,2,3,4-tetrasubstituted pyrrole derivatives from one-pot three-component reaction of commercially available primary amines, 1,3-dicarbonyl compounds, and trans-β-nitrostyrene at room temperature. Thirty-three corresponding pyrroles, of which eight are novel and have been reported for the first time, were synthesized in high to excellent yields in lactic acid media and characterized by spectroscopic analysis. In all examined cases, lactic acid represented many advantages, including shorter reaction time, ease of product isolation, higher yields, no by-products, no chromatographic process, and lower volatility in the reaction. This bio-based green solvent can also be recycled and reused three times without loss of its efficiency as a catalyst and solvent.