Alkene-containing boronic ester 2o formed in moderate yield, and a di-borylation product (2p) was smoothly synthesized from the corresponding di-thioether upon the use of twice the amount of pinacolborane and 2.5 times the charge. Tertiary pinacolboronic esters 2q-2s were successfully formed under standard conditions. In contrast, the secondary product 2t would only form after adjustments of the reaction conditions (MeCN as solvent, 10 equiv. HBpin). This sluggish reactivity for secondary positions proved beneficial as we turned our attention to more advanced substrates derived from pharmaceuticals and natural products (Scheme 1B), and the derivatized antihistamine terfenadine selectively underwent desulfurative borylation at the tertiary site in the presence of a secondary phenyl thioether (2u). Furthermore, the phenyl thioether based on the core structure of rosuvastatin, used for treatment of cardiovascular disease, furnished product 2v, whereas phenyl thioethers based on the phosphodiesterase inhibitor roflumilast, the muscarinic antagonist diphenidol, as well as the acetylated salicin derivative formed the targeted borylation products in moderate to good yields (2w-2y). Furthermore, allylic thioethers were amenable to desulfurative borylation, furnishing allylic boronic esters derived from myrtenol, geraniol and perillyl alcohol in good yields (2z-2ab). Here, the formation of regioisomers was observed with clear preference for primary, less sterically hindered sites. Finally, the borylation procedure proved scalable and furnished 1 gram of product 2a, demonstrating the potential of the procedure for practical larger batch To probe the mechanism of the catalyst-free direct borylation reaction, a radical trap experiment was carried out using thioether 1zz that contains a pendant alkene sidechain. When subjected to standard conditions, 5-exo trig product 2ac was not observed (Figure ). Instead, the linear product 2ad was obtained in 77%, indicating that the transformation does not proceed via a C-centered radical with a lifetime sufficient for cyclization. This finding is in line with our previous findings, where benzylic phenyl thioethers were demonstrated to preferentially transform into carbanions under similar electroreductive conditions. Indeed, the expected reactivity of such carbanionic intermediates is compatible with the observed regioselectivity for allylic products formed herein (Figure ). As such, we propose that the desulfurative borylation proceeds via a paired electrolysis mechanism, initiated by cathodic single electron transfer (SET) to the thioether substrate. This SET sets off mesolytic C-S bond cleavage to furnish phenylthiolate anion and a benzylic open-shell species. The latter rapidly undergoes a radical-polar crossover via a second SET to furnish a carbanion, that is trapped by the reductively stable pinacolborane (see ESI). The resulting borohydride intermediate undergoes subsequent oxidation at the anode to furnish the boronic ester product along with hydrogen gas. In addition, oxidation of the supporting electrolyte NBu4BH4 to H2 and the phenylthiolate by-product to the corresponding disulfide maintain the charge balance in the electrochemical cell.