L-Proline-catalysed sequential four-component on water protocol for the synthesis of structurally complex heterocyclic ortho-quinones

The L-proline-catalyzed synthesis of 7-(aryl)-8-methyl-10-phenyl-5H-benzo[h]pyrazolo[3,4-b]quinoline-5,6(10H)-diones via the four-component sequential reaction of phenylhydrazine, 3-aminocrotononitrile, substituted benzaldehydes and 2-hydroxynaphthalene-1,4-dione is described. This on water protocol proceeds in high atom economy and leads to the generation of two rings, together with two C-C, one C-N and two C=N bonds in a single operation. The environmental advantages of the method include short reaction time, excellent yield, easy work-up, and the absence of extraction and chromatographic purification steps.