Cascade Reaction of Isatins with 1,1-Enediamines: Synthesis of Multisubstituted Quinoline-4-carboxamides

A one-step methodology for the synthesis of multisubstituted quinoline-4-carboxamides was developed by simply refluxing a mixture of isatins 1 and various kinds of 1,1-enediamines 2–4 in a reaction catalyzed by NH₂SO₃H. As a result, a series of quinolone-4-carboxamides were produced through a novel cascade reaction mechanism. This reaction involved the formation of the quinoline ring accompanied by the formation of an amide bond in one step. Accordingly, this protocol is suitable for combinatorial and parallel syntheses of quinolone-4-carboxamide drugs or natural products.