Reactions with 1a-D under the standard conditions resulted in product 3b-D as the only regioisomer, together with the corresponding disulfide byproduct in 11% yield (Scheme 3c). The reaction with 1b-D2 delivered product 3b-D2 in moderate yield together with the disulfide byproduct (Scheme 3d). To reach these products through pathway II, complete selectivity in b- Intermediates B-F were not possible to locate since the structures always converged to intermediate A¢, indicating that the reaction proceeds through pathway Ia. We also computed the reaction profiles with Me2-VBX 1b, and o-Me-VBX 1c, which resulted in very similar energies (Figures ). The benefit of reagent 1b might be explained by the lower electrophilicity of the iodine compared to 1a, thus resulting in cleaner reactions without formation of disulfide byproduct. The energy profile for the reaction of 1a and 2a in the absence of base had a considerably higher TS energy (43 kcal/mol), which is in accordance with the observed low reactivity without base (Figure ).