Chemo‐ and Regioselective Synthesis of Functionalized 1H‐imidazo[1,5‐a]indol‐3(2H)‐ones via a Redox‐Neutral Rhodium(III)‐Catalyzed [4+1] Annulation between Indoles and Alkynes

Abstract Alkynes generally serve as C 2 synthons in transition‐metal‐catalyzed C−H annulations, herein, exploiting electron‐deficient alkynes as unconventional C 1 synthons, the chemo‐ and regiospecific synthesis of functionalized 1 H ‐imidazo[1,5‐ a ]indol‐3(2 H )‐ones via a redox‐neutral rhodium(III)‐catalyzed [4+1] annulation of N ‐carbamoyl indoles has been achieved. This process is characterized by high chemo‐ and regioselectivity, broad substrate scope, good tolerance of functional groups, moderate to high yields and mild redox‐neutral conditions, thus affording a robust approach to access valuable 1 H ‐imidazo[1,5‐ a ]indol‐3(2 H )‐ones. magnified image