Synthesis of Fused or Spiro Polyheterocyclic Compounds via the Dehydrogenative Annulation Reactions of 2-Arylindazoles with Maleimides.

A dehydrogenative annulation of 2-arylindazoles with maleimides for the switchable synthesis of indazolo[2,3-a]pyrrolo[3,4-c]quinolinones or spiroindolo[1,2-b]indazole-11,3'-pyrrolidinones is presented. Mechanistically, the formation of the title compounds involves a Rh(III)-catalyzed C-H metalation of 2-arylindazole, followed by maleimide insertion and intramolecular cyclization. Interestingly, the selectivity to form the fused or spiro compounds could be switched by resorting to different additives. The notable features of this protocol include simple substrates and excellent atom economy and regioselectivity.