HFIP-mediated multicomponent reactions for the synthesis of fluorescent quinoline-fused pyrroles

Abstract

Herein we report a metal-free multicomponent reaction for the synthesis of diverse quinoline-fused pyrroles using 1,1,1,3,3,3-hexafluoro isopropanol (HFIP) as a reaction medium cum promoter. The reaction of aryl glyoxals, 4-hydroxycoumarin or other cyclic 1,3-dicarbonyl compounds, and 6/5-aminoquinoline or 5-aminoisoquinoline in the HFIP medium under reflux conditions provide regioselective corresponding quinoline/isoquinoline-fused pyrroles. This methodology is applicable to a wide range of substrates and provided quinoline/isoquinoline-fused pyrroles in good to very good yields. The notable features of this protocol are metal-free conditions, operational simplicity, easy purification, and the presence of bioactive pyrrole, quinoline/isoquinoline and cyclic 1,3-dicarbonyl moieties in the products. Most of the synthesized fused pyrroles exhibit fluorescence properties. The photophysical properties of all the synthesized fused pyrroles were studied by recording UV–Visible and steady-state fluorescence spectroscopy. Compounds 4a, 4e, 4f, 4h, 4i and 4s showed very good fluorescence quantum yields.