Synthesis of biologically important, fluorescence active 5-hydroxy benzo[g]indoles through four-component domino condensations and their fluorescence “Turn-off” sensing of Fe(iii) ions?

RSC Advances Pub Date: 2015-06-08 DOI: 10.1039/C5RA05780A

Abstract

Several highly substituted 2-pyrrolyl-2-cyanoacetamides were prepared through four-component domino condensation of various easily available 1,3-dicarbonyl compounds, amines, arylglyoxals and malononitrile. Subsequently these cyanoacetamide derivatives were converted into biologically important 5-hydroxy benzo[g]indoles through thermal cyclization under metal-free conditions. The synthesized 5-hydroxy benzo[g]indoles are fluorescence active with good quantum yields (ΦF = ～0.50). They also show excellent fluorescence “Turn-off” sensing of Fe3+ ions (detection limit = ～1.2 × 10?6 M). The interaction of 5-hydroxy benzo[g]indoles with Fe3+ ions can also be monitored through UV-Vis spectral change and naked-eye colour change in the presence and absence of UV radiation. The 1H NMR titration unambiguously proves the formation of a complex between 5-hydroxy benzo[g]indoles and Fe3+ ion through the coordination of –OH groups with the metal. The binding constant of the complex (metal?:?ligand = 1?:?1) has been measured using Benesi–Hildebrand equation and found to be ～7.97 × 103 M?1.

Graphical abstract: Synthesis of biologically important, fluorescence active 5-hydroxy benzo[g]indoles through four-component domino condensations and their fluorescence “Turn-off” sensing of Fe(iii) ions
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