Water-mediated, green, and efficient synthesis of bisquinolones under catalyst-free conditions

Water-mediated, green, and efficient synthesis involving condensation of 4-hydroxy-1-methylquinoline-2(1H)-one (3) with different aromatic and heterocyclic aldehydes (4a–n) leading to 3,3′-(arylmethylene)-bis-(4-hydroxy-1-methylquinolin-2(1H)-one) 5(a–n) under catalyst-free conditions is described. This reaction has an easy workup without using column chromatography and provides excellent yields of the products in shorter reaction times. It does not require any catalyst and uses water as the medium which is the greenest solvent. 3 required in this work was itself obtained by condensation of N-methylaniline (1) with malonic acid (2) in the presence of POCl₃ using a previously reported procedure.