When employing density functional theory (DFT) calculations to further study the reaction pathway, it was observed that the complexation of the radical cation 1a •+ with a simple alkene (propene) to form IM-I •+ , is exergonic by 1.2 kcal/mol (Fig. ). Subsequent insertion of the alkene fragment into the BCB scaffold was found to be a kinetically facile process (TS-Ia), with a free energy barrier of 10.0 kcal/mol with respect to the preceding IM-I •+ . To rationalise the regiochemistry of this initial bond forming process, all other possible transition states (TS-Ib, TS-Ic, and TS-Id) were computed and were all found to have significantly higher free energy barriers. From TS-Ia, formation of the subsequent intermediate IM-II •+ was determined to be exergonic by 5.5 kcal/mol. Upon closer analysis of IM-II •+ we identified that the spin density of the radical cation is highly localised on the propene α-carbon (C8), a result that agreed with the outcome of the radical trapping experiments which suggested that a carbon radical is present at this position (Fig. ). However, in order to rationalise the apparently contradictory results of the radical clock experiments, we calculated the spin densities for the corresponding intermediate with substrate 2z (IM-2z •+ , Fig. ) and found that, in this case, no spin density is localised on the carbon adjacent to the cyclopropane (C8). From this, we can conclude that the distribution of spin and charge density in the intermediate following the initial interaction of 1a •+ with olefins is highly dependent on the nature of the alkene substituents. The final C-C bond formation step in the mechanism (TS-II) was found to be a barrierless process, with an estimated free energy of -14.5 kcal/mol using a restrained calculation (see Supplementary Information). Reduction of the thermodynamically stable 3a •+ (-20.9 kcal/mol), can then occur from either the reduced photocatalyst or a neutral BCB molecule to turn over the radical chain and generate BCH product 3a.