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.

Alkynes generally serve as C2 synthons in transition‐metal‐catalyzed C−H annulations, herein, exploiting electron‐deficient alkynes as unconventional C1 synthons, the chemo‐ and regiospecific synthesis of functionalized 1H‐imidazo[1,5‐a]indol‐3(2H)‐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 1H‐imidazo[1,5‐a]indol‐3(2H)‐ones. [ABSTRACT FROM AUTHOR]