An efficient and practical Cu(I)-catalyzed oxidative cyclization cascade reaction of diverse amines, alkyne esters and maleimides has been developed. The reactions can afford 4,6-dioxopyrrolo[3,4-b]pyrrole-2,3-dicarboxylates and related derivatives with satisfactory yields by altering the reaction conditions slightly. The substrate scope highlights the flexibility of the catalyst, and a reaction mechanism is also proposed.

An efficient Pd(II)-catalyzed approach for the direct synthesis of indolo[3,2-a]pyrrolo[3,4-c]carbazole-6,8-diones has been developed from both free and protected (NH) indoles and maleimides via a regioselective tandem oxidative coupling reaction. The yields are moderate to excellent. In addition, 2-substituted indoles are suitable substrates in this protocol, leading to the formation of indolylmaleimides. The present methodology provides a concise route to highly functionalized indolopyrrolocarbazole derivatives.

A highly efficient synthetic strategy for synthesizing 3-arylsuccinimides has been developed from arenediazonium tetrafluoroborates and maleimides in the presence of TiCl3. The reactions generated 3-arylsuccinimides in satisfactory yields under mild reaction conditions. In addition, 3-arylmaleimides were obtained by the coupling of arenediazonium tetrafluoroborate and maleimides catalyzed by CuCl. This methodology provided the selective and tunable synthesis of two classes of products by simply switching different metal reagents. The methods are simple, efficient and practical.