Enantioselective Synthesis of α-Chiral Propargylic Silanes by Copper-Catalyzed 1,4-Selective Addition of Silicon Nucleophiles to Enyne-Type α,ß,γ,δ-Unsaturated Acceptors

A copper-catalyzed deconjugative addition of silicon nucleophiles to a broad range of enyne-type alpha,ss,gamma,delta-unsaturatedacceptors with high enantiocontrol is reported. The method is 1,4-selective with hardly any formation of the 1,6-adduct. The double-bond geometry is shown to be critical for achieving this chemoselectivity: exclusive 1,4-addition for E and predominant 1,6-addition for Z. By this, E-configured enynoates, enynamides, and enynones have been converted to the corresponding a-chiral propargylic silanes with excellent enantiomeric excesses.