Water Mediated, Eco-friendly Enantioselective Synthesis of Indole Substituted N-heterocyclic Compounds via Friedel-Crafts Alkylation

Background: Among the nitrogen heterocycles, quinolones and their derivatives represent the most important class of organic scaffolds that attract the interest of both medicinal and synthetic chemists. And these molecules possess a large number of biological and pharmacological properties. Here, we have synthesized 3-(1-(1H-indol-3-yl)-3-oxo-3-phenylpropyl)-4-hydroxy-1-methylquinolin-2( 1H)-ones 5 in presence of L-proline through the intermediacy of 4-hydroxy-1-methyl-3-(3-oxo-3-phenylprop- 1-en-1-yl) quinolin-2(1H)-one 3. Methods: All the compounds 5(aa-ce) have been synthesized in step-wise, one-pot with sequential addition and one-pot process with all substrates present from the outset methods under green conditions. The structure of the product was established based on its spectral properties IR, H-1-NMR, C-13-NMR and Mass. Results: In this work we describe the synthesis of 3-(1-(1H-indol-3-yl)-3-oxo-3-phenylpropyl)-4-hydroxy- 1-methylquinolin-2(1H)-ones 5(aa-ce) by condensation of 4-hydroxy-1-methyl-2-oxo-1,2-dihydroquinoline- 3-carbaldehyde 1, with acetophenone 2(a-c) and indole 4(a-e) in the presence of L-proline and water. Conclusion: We have synthesized new series of indole substituted N-heterocyclic chalcones via Friedel-Crafts alkylation under green condition. The syntheses are water mediated and eco-friendly involving easy workup: moreover they gave high yields without the need of costly catalyst and column chromatography.