Evidence is presented that the formation of aryl vinyl sulfide cation radicals from the corresponding neutral precursors via reaction with tris(4-bromophenyl)aminium hexachloroantimonate in the context of a cation radical Diels−Alder addition to 1,3-cyclopentadiene does not occur via outer sphere electron transfer but by a mechanism involving strong covalent interaction between the aminium salt acting as an electrophile and the aryl vinyl sulfide substrate acting as a nucleophile.