The success of this approach relies on three key features. Firstly, the radical cation RC2a needs to be regioselectively deprotonated to form the radical R2a. No product results resulting from R2a' has been identified but we cannot exclude that such products are formed in small amount (Scheme 11A). The calculated pKa values for the C(2)-H and C(3)-H bond (see scheme 11A) are very close and cannot be used to rationalize this result. Nevertheless, this type of selectivity for the less substituted position is well-established and can be rationalized by both steric and stereoelectronic effects. Secondly, in principle all three amines 1a, 2a and 3a present in solution can be easily oxidized by the Ir(III)* catalyst excited state. However, only RC1a and RC2a (calculated pKa 51.4 and 52.7 in DCE) are undergoing deprotonation to generate α-aminoalkyl radicals. The deprotonation of the bicyclic radical RC3a (pKa 58.4) is much less favorable and no product resulting from the bicyclic radical R3a has been observed (Scheme 11B). A separate attempt to achieve allylation of pure 3a under our standard reaction conditions led only to partial decomposition of the starting material without formation of an allylated product. Since the oxidation potentials of all three amines 1a, 2a and 3a are close and well below the oxidation potential of the excited Ir(III)* catalyst, we believe that the efficacy of the whole process is due to the fact that oxidation of 3a, which is becoming increasingly important as the reaction proceeds, is not leading to its decomposition as long as 1a and 2a are present in solution due to rapid electron transfers between the different amines in solution (Scheme 11C). Such rapid electron transfers involving radical cations are well-documented in the literature and have led to the use of triarylaminium radical cation as organic mediator in electro-organic synthesis. Scheme 11. Possible mechanism for the [3+3] radical annulation and analysis of (A) the regioselectivity of radical formation, (B) the selective formation of bicyclic radicals, and (C) the equilibrium between the different radical cations formed during the reaction.