L-Proline-promoted three-component reaction of anilines, aldehydes and barbituric acids/malononitrile: regioselective synthesis of 5-arylpyrimido[4,5-b]quinoline-diones and 2-amino-4-arylquinoline-3-carbonitriles in water
A green and efficient one-pot process to achieve 5-aryl-pyrimido[4,5-b]quinoline-dione derivatives, using a three-component reaction involving anilines, aldehydes and barbituric acids was developed. This protocol was accomplished efficiently using L-proline as catalyst in an aqueous medium to give the corresponding products in high yield. Also, 2-amino-4-arylquinoline-3-carbonitrile derivatives were obtained by replacing the barbituric acid with malononitrile in the designed protocol. The catalytic activity of L-proline in these reactions was tested over a set of aldehydes and amines, demonstrating that it is reactive towards a variety of functionalities. The multicomponent reactions showed good regioselectivity, and computational studies were used to investigate the selectivity.