ENANTIOSELECTIVE COPPER-CATALYZED 1,4-ADDITION OF GRIGNARD-REAGENTS TO ALPHA,BETA-UNSATURATED CARBONYL-COMPOUNDS

The enantioselective copper-catalyzed 1,4-addition of Grignard reagents to alpha,beta-unsaturated carbonyl compounds was studied with the following Cu(I) compounds as catalyst precursor and 1,2:5,6-di-O-isopropylidene-3-thio-alpha-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.