Structure and Reactivity of Aromatic Radical Cations Generated by FeCl₃

This paper describes the isolation and characterization of an aromatic radical cation generated by FeCl₃. X-ray crystallographic analysis and kinetic studies reveal the mechanism of the generation of aromatic radical cation. In the solid state, a tight ion-pair of a radical cation with FeCl₄^- is observed. Leveraging the efficient generation of the radical cation-FeCl₄^- ion pair, we explore a radical cation-induced cycloaddition of trans-anethole initiated by catalytic amount of FeCl₃. Both [4+2] cycloaddition and [2+2] cycloaddition with a broad substrate scope are also described. Moreover, a 100 g-scale reaction is demonstrated with the use of 1 mol % of FeCl₃ as a simple and a highly active initiator.