Enantioselective Copper‐Catalyzed 1,4‐Addition of Grignard Reagents to α,β‐Unsaturated Carbonyl Compounds

The enantioselective copper‐catalyzed 1,4‐addition of Grignard reagents to α,β‐unsaturated carbonyl compounds was studied with the following Cu I compounds as catalyst precursor and 1,2:5,6‐di‐ O ‐isopropylidene‐3‐thio‐α‐ D ‐glucofuranose (Hsiig) as chiral ligand: CuI, iodo[bis(dibutylsulfide)]copper(I), [Cu(siig)], [Cu(siig)(pp)] (pp =1,2‐bis)(diphenylphosphinoethene), and tetrakis[iodo(tributylphosphine)]copper(I). The addition of BuMg halides to cyclohex‐2‐en‐1‐one was tested under several reaction conditions. The chemical yields and regioselectivities for this reaction were, in all cases, larger than 90 and 98%, respectively, and independent of the experimental conditions. The enantioselectivity was strongly dependent on the reaction conditions and reached a maximum of 60%. Several other substrates were also tested in the above reaction. The X‐ray crystal structure for [Cu(siig)(pp)] was determined by X‐ray crystallography.