Asymmetric Addition of in situ Formed Alkynylzincs to Ketones

Significance

Aromatic and aliphatic ketones can be enantioselectively converted into chiral tertiary propargylic alcohols via addition of terminal alkynes in the presence of a Cu(OTf)₂/camphorsulfonamide catalyst and ZnMe₂. Enantiomeric excesses were generally good to excellent for the reaction of aromatic ketones with phenylacetylene, whereas sterically hindered ketones and poorly nucleophilic alkynes afforded lower yields and/or ee values. The reaction was also extended to a selective 1,2-addition of phenylacetylene to an α,β-unsaturated ketone, contrasting with the traditional regioselectivity of Cu-catalyzed processes.