Enantioselective and Regiodivergent Synthesis of Propargyl‐ and Allenylsilanes through Catalytic Propargylic C−H Deprotonation

We report a highly enantioselective intermolecular propargylic C−H silylation mediated by an η³-propargyl/allenyl Ir complex. Under reagent-controlled protocols, propargylsilanes resulting from C(sp³)−H functionalization, as well the regioisomeric, synthetically versatile allenylsilanes, could be obtained with excellent levels of enantioselectivity and good to excellent control of propargyl/allenyl selectivity.

Abstract

We report a highly enantioselective intermolecular C−H bond silylation catalyzed by a phosphoramidite-ligated iridium catalyst. Under reagent-controlled protocols, propargylsilanes resulting from C(sp³)−H functionalization, as well the regioisomeric and synthetically versatile allenylsilanes, could be obtained with excellent levels of enantioselectivity and good to excellent control of propargyl/allenyl selectivity. In the case of unsymmetrical dialkyl acetylenes, good to excellent selectivity for functionalization at the less-hindered site was also observed. A variety of electrophilic silyl sources (R₃SiOTf and R₃SiNTf₂), 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, 1,3-enynes, and drug derivatives were successfully employed as substrates. Detailed mechanistic experiments and DFT calculations suggest that an η³-propargyl/allenyl Ir intermediate is generated upon π-complexation-assisted deprotonation and undergoes outer-sphere attack by the electrophilic silylating reagent to give propargylic silanes, with the latter step identified as the enantiodetermining step.

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