Green and eco-friendly synthesis of quinolone substituted indolyl- 4H -chromenes via C–C bond formation

A novel and green strategy for the construction of biologically relevant substituted indolyl-4H-chromenes scaffolds is reported using L-proline as a catalyst and water as a promoter solvent. The catalytic system offers wider applicability, crossing over a variety of substrates, besides affording exclusively the desired product in shorter reaction times and high yields. L-proline-Water was found to be an efficient and cheaper catalytic system for regioselective synthesis of indolyl-4H-chromenes. The reaction between 4-hydroxy-1-methyl-2-oxo-1,2-dihydroquinoline-3-carbaldehyde (1) with active methylene compounds (2a–b) and substituted indoles(3a–f) in the presence of L-proline afforded quinolone substituted indolyl-4H-chromenes (4a–l) in excellent yields. Furthermore, the reactions involve easy workup giving high yields without the need of column chromatography, making it one of the most ideal conditions for green chemistry.