Electrophilic Activation of S–Si Reagents by Silylium Ions for Their Regio‐ and Diastereoselective Addition Across C–C Multiple Bonds

A regioselective silylium‐ion‐promoted thiosilylation of internal C−C triple bonds with control over the double bond geometry is described. Both a C(sp²)−S and a C(sp²)−Si bond are formed with a trans relationship in this two‐component reaction of an alkyne and a thiosilane. The resulting orthogonally functionalized C−C double bond can be chemoselectively defunctionalized or further processed by cross‐coupling reactions with the alkene configuration retained. The procedure is also applicable to the regio‐ and diastereoselective thiosilylation of terminal allenes to arrive at allylic thioethers containing a vinylsilane unit. These reactions involve the electrophilic activation of the S−Si reagent, both a silylated thiophenol and even alkylthiol derivative, by an in situ‐generated carbocation intermediate. The catalytic cycle is maintained by a bissilylated aryl‐ or alkylsulfonium ion as a shuttle for the cationic silicon electrophile. Its independent preparation and structural characterization by X‐ray diffraction are also reported.