Ruthenium(II)-Catalyzed Redox-Neutral [3+2] Annulation of Indoles with Internal Alkynes via C-H Bond Activation: Accessing a Pyrroloindolone Scaffold.

Ru(II)-catalyzed redox-neutral [3+2] annulation reactions of N-ethoxycarbamoyl indoles and internal alkynes via C-H bond activation are reported. This method features a broad internal alkyne scope, including various aryl/alkyl-, alkyl/alkyl-, and diaryl-substituted alkynes, good to excellent regioselectivity, diverse functional group tolerance, and mild reaction conditions. The N-ethoxycarbamoyl directing group, temperature, CsOAc, and ruthenium catalyst proved to be crucial for conversion and high regioselectivity. Additionally, preliminary mechanistic experiments were conducted, and a possible mechanism was proposed.