Copper(I)-Catalyzed Enantioselective Addition of Enynes to Ketones

A copper­(I)-catalyzed enantioselective addition of enynes to ketones was developed. The method allows facile construction of enantiomerically enriched tertiary alcohols using skipped enynes as stable hydrocarbon pronucleophiles. The combination of a soft copper­(I)-conjugated Brønsted base catalyst with a chiral diphosphine ligand, (S,S)-Ph-BPE, enabled chemoselective deprotonation of the skipped enynes in the presence of ketones bearing intrinsically more acidic α-protons. The catalytically generated chiral allylcopper species enantio-, diastereo-, regio-, and chemoselectively reacted with ketones, thereby demonstrating excellent substrate generality with functional group tolerance. The skipped enyne moieties of the pronucleophiles were exclusively converted to cis-conjugated enynes, which will eventually allow for further versatile transformations.