A convenient synthesis of 2,4-diarylpyrroles from β-cyanoketones via reductive rearrangement of in situ generated 2-aminofurans

Abstract

A new, efficient, and regioselective method for the synthesis of 2,4-diarylpyrroles based on readily available β-cyanoketones has been developed. The cascade reaction proceeds through the in situ formation of 2-aminofurans in polyphosphoric acid, followed by their reductive rearrangement under the action of zinc dust and phosphorous acid. Optimized conditions (PPA 87% / H3PO3 5:1, 160 °C) allow for the preparation of the target pyrroles with yields ranging from 26 to 83%. The compatibility of the method with alkyl, thioether, and amino groups has been demonstrated, and the reactivity limitations associated with ortho-substitution and the presence of alkoxy groups have been investigated.