[PC] + /[PC]* = -1.11 V vs SCE). Therefore, the thermodynamic feasibility of a single electron transfer (SET) reduction of S8 by the excited thioxanthone was also excluded by means of the cyclic voltammetry measurement (Fig. ). followed by a radical-radical coupling process with the ambiphilic iminyl radical 16 from the opposite, sterically accessible side to produce the desired trans-diamine 8. We speculated that the observed regioselectivity of this reaction might be mainly guided by the stability, electronic property, as well as steric hindrance of the generated C-centered radical after the addition of the N-centered amidyl radical to H1. The addition to H1 at the C2 position generated a stabilized benzyl radical (17), while the addition at the C3 position would yield a highly nucleophilic α-aminoalkyl radical (18). Although C3 is relatively more nucleophilic than C2, the polar match of ambiphilic N-centered iminyl radical with stabilized benzyl radical ( ) might be higher than that with highly nucleophilic α-aminoalkyl radical (18). Moreover, the steric hindrance of the generated C-centered radical undoubtedly played an important role in regiocontrol. Clearly, radical 17 was less sterically hindered than radical 18, facilitating the radical-radical cross-coupling of C-centered radical with N-centered iminyl radical to furnish the desired diamine product. Notably, while 17 is a nucleophilic and relatively stabilized benzyl radical, the radical-radical cross-coupling of 17 with the electrophilic amidyl radical 15 was not observed in the reaction (Fig. ).