Herein, we report a mechanistic exploration of the unusual FeCl3-mediated hydroarylation of N-Ac indoles. Electron density topology analysis of a crystal, in situ IR monitoring, Hammett and Taft studies as well as DFT computations allowed us to determine that activation of acetyl with FeCl3 and of the C2[double bond, length as m-dash]C3 bond with a proton is involved.