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(sp 2 )-S and a C(sp 2 )-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.