Pyrrolocarbazoles are important structural motives present in many natural products and pharmaceuticals. Particularly, pyrrolo[3,4-a]carbazole-1,3-diones have attracted much attention as analogues of bioactive compounds, such as anticancer agent granulatimide. Surprisingly, only a few methods for the synthesis of these compounds have been reported in the literature, and they are almost limited to the Diel-Alder cycloaddition of 3-vinylindoles.
We have recently developed a multicomponent synthesis of polysubstituted anilines starting from a,b-unsaturated carbonyls, isocyanides and dienophiles. Here we report the application of this tandem [4+1]-[4+2] cycloaddition procedure for the synthesis of 4-amino-5-arylisoindoline-1,3-diones, which are then cyclized by means of a metal catalyzed intramolecular C-N coupling, affording structurally diverse, natural product-like pyrrolo[3,4-a]carbazole-1,3-diones with high yields and selectivities.