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.