Iridium-Catalyzed Regio- and Enantioselective Propargylic C−H Silylation

ABSTRACT: We report a highly enantioselective intermolecular silylation of the propargylic C(sp3)−H bonds of alkynes for the formation of propargylic silanes. The optimized protocol afforded enantioenriched α-silylated alkynes in good to high yield with excellent levels of stereocontrol under mild conditions. A variety of silyl triflates, either commercial or in situ-generated, were used as the silylation reagents, and a broad range of simple and functionalized alkynes, including aryl alkyl acetylenes, dialkyl acetylenes, and 1,3-enynes, were successfully employed as substrates. In the case of dialkyl acetylene substrates, silylation took place in a highly regi-oselective manner. Preliminary mechanistic experiments suggest a catalytic cycle in which electrophilic addition of the silyl triflate reagent to the Ir center and subsequent deprotonation of a dicationic Ir–alkyne complex are key steps.