Earlier experimental observations were the starting point of this mechanistic study. Vinylation of S-nucleophiles led exclusively to internal alkenes 3 (E:Z ratio generally >20:1), indicating that VBX does not react through a vinylic SN2 mechanism 27 (Scheme 1b). Alkenes 3 were formed also in the presence of radical traps, and the reaction slowly proceeded also without base. Furthermore, core-substituted Me2-VBX proved superior to the standard VBX as formation of disulfide (ArS)2 byproduct was suppressed. On account of experimental observations, literature mechanisms with vinyliodonium salts and the reported mechanistic investigations of S-alkynylations with EBX, A concerted asynchronous alternative in between these two extremes is also possible.