Both DFT calculations and experimental studies support the formation of a-bromoketone 9 as an important intermediate in this cross-nucleophile coupling. This umpolung event is mediated by benzoidoxole 2c, and can occur by three possible mechanisms. Pathway A and pathway B are analogous mechanisms involving Oenolonium-II and C-enolonium-II', respectively, in which bromide interacts with the I(III) through a halogen bond (3.17 and 3.20 Å, respectively). These species then undergo a reductive coupling step to give a-bromoketone 9. These Br-I interactions might explain the lack of by-products. As mentioned above, the formation of by-products such as dimers (Nu 2 = 1) or a-hydroxy ketones (Nu 2 = OH -, Scheme 3e) has been a major limitation in similar I(III)mediated umpolung approaches. We have also observed by-product formation when using other I(III) reagents, e.g., with 2a in our previous work, and with 2e in the optimization experiments described in this paper (Scheme 1). Alternatively, pathway C can occur via C-enolonium-III, which is formed by ligand rearrangement around the I(III) center of C-enolonium-II. In pathway C, the bromide atom is not interacting with the I(III) center (Br-I distance is 5.16 Å) of C-enolonium-III. From here, a nucleophilic attack of the Br -on the very electrophilic a-C of Cenolonium-III also leads to a-bromoketone 9 (16.2 kcal/mol for isomerization and 15.8 kcal/mol for the SN2 step). The DFT calculations do not show a strong preference for any of the three pathways explored. However, if Cenolonium-III is involved (pathway C), we would expect the highly electrophilic enolonium (C-enolonium-III) to react also with any of the nucleophiles present in the reaction mixture, such as starting enol 1 or HO -(Scheme 3e) to form by-products. The control experiment in Scheme 3b also shows that a-bromoketone 9 is the sole product formed in the absence of the heteronucleophile (Nu 2 ). The absence of by-products may be explained through a reaction pathway in which an intramolecular reaction results in formation of the C-Br bond formation (pathways A and B), rather than through an intermolecular nucleophilic displacement of I(III) on the enolonium intermediates (pathway C).