To further understand the mechanism of the cross-nucleophile-coupling reaction mediated by bromobenzoidoxole 2c, we turned to DFT calculations at the B3LYP and M06 functional levels using the Gaussian 16 software (see Supporting Information for more details). The calculations were carried out using the sum of the energies of enolate species I and iodine(III) reagent 2c as the reference point (G = 0 kcal/mol) of the energy profile (Figure , middle). The enolate can attack the iodine atom either through the oxygen or through the carbon of the enolate, leading to formation of at least three possible low-energy enolonium intermediates (O-enolonium-II (-2.0 kcal/mol), C-enolonium-II (-3.0 kcal/mol), and C-enolonium-II´ (0.2 kcal/mol). In all cases, the formation of the enolate-iodine bond occurs in the position trans to the phenyl-I substituent, inducing an elongation of the Br-I bond. In the starting compound 2c, the Br-I bond is short, i.e., 2.9 Å. This bond length is increased in O-enolonium-II (3.17 Å), and even more so in C-enolonium-II´ (3.20 Å) and C-enolonium-II (3.29 Å). These distances are similar to those found in structures with a halogen bond between iodine and bromine atoms. The three calculated intermediates are almost isoenergetic and they could, therefore, be in equilibrium. The direct reductive ligand coupling of the bromine and enolate fragments of these enolonium intermediates was calculated to be feasible. For example, TSII-IV and TSII´-IV have calculated activation energies of 18-19 kcal/mol from their respective enolonium intermediates, O-enolonium-II (-2.0 kcal/mol) and C-enolonium-II´ (0.2 kcal/mol). Interestingly, a transition state was found for the isomerization of the enolate substituent, which rotates from the trans to the cis position relative to the phenyl-I bond, displacing the bromine atom from the coordination sphere of the iodine. This transition state (TSII-III, DDG ‡ = 16.2 kcal/mol) is low in energy, and leads to enolonium intermediate C-enolonium-III. From here, backside attack by the bromide (TSIII-IV) on the a-carbon in C-enolonium-III has the lowest calculated energy for C-Br formation (DDG ‡ = 15.8 kcal/mol). In contrast, the syn attack represented by TS ´III-IV is too high energy to take place under these reaction conditions (DDG ‡ = 35.7 kcal/mol). Thus, our DFT calculations show that the formation of the a-bromo ketone intermediate INT-IV is feasible under the reaction conditions starting from the enolate and iodine(III) reagent 2c. This pathway is possible in the absence of any external nucleophilic anion. After that, intermediate a-bromoketone 9 evolves via a nucleophilic displacement upon reaction with the heteronucleophiles (Scheme S2).