The synthesis of 1H-benzo[f]isoindole derivatives was achieved by the cascade radical cyclization–cyclization reaction of the active methine substrate having an allyl group and phenyl group as different two radical acceptors. This oxidative transformation proceeded by using iron(III) chloride FeCl3 as a mild oxidant via the intramolecular radical addition to the allyl group followed by the second radical addition to the phenyl group.