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The intermediate-dependent green and efficient synthesis of dimeric quinolones 4a-l and 7a-l by the Knoevenagel condensation followed by Michael-type addition of 4-hydroxy-1-methylquinolin-2(1H)-one 1a, b to indole-3-aldehydes 2a-f and aromatic aldehydes 5a-l in water through the condensed compound 3a-l under catalyst-free conditions is described. This reaction was found to be environmentally friendly, has easy-workup and shorter reaction times giving good yields of the product without the need for its isolation using column chromatography. [ABSTRACT FROM AUTHOR]