FeCl₂/TBAC has been found to be highly active for the construction of indoline-fused tetrahydroisoquinolines using aryltetrahydroisoquinolines and active methylene as simple reactants. The transformation was proposed to proceed via domino coupling reactions between C_sp³–H and C_sp³–H, and subsequently C_sp³–H and C_sp²–H, respectively. The EPR spectra have been acquired to analyse the catalytically active species, Fe³⁺OO˙ and Fe³⁺, which accelerated the reaction via HAT and SET processes, respectively.