Facile 1,1-Carboboration Reactions of Acetylenic Thioethers

The acetylenic thioether PhSCCSPh undergoes a rapid 1,1-carboboration reaction with facile −SPh migration upon treatment with B­(C6F5)3 to yield the borylated ketene dithioacetal product (PhS)2CC­(C6F5)­B­(C6F5)2 (8a). The X-ray crystal structure analysis revealed an intramolecular sulfur–boron contact. The thioether PhCCSPh undergoes an analogous 1,1-carboboration reaction with B­(C6F5)3. The resulting vicinal S/B frustrated Lewis pair undergoes 1,2-addition reactions to terminal acetylenes to give the respective zwitterionic six-membered heterocyclic sulfonium/borate products (all three examples were characterized by X-ray diffraction).