FIRST ENANTIOSELECTIVE ADDITION OF DIETHYLZINC AND DIMETHYLZINC TO PROSTEREOGENIC KETONES CATALYZED BY CAMPHORSULFONAMIDE-TITANIUM ALKOXIDEDERIVATIVES

The reaction of diethylzinc or dimethylzinc with prostereogenic ketone s, in the presence of a stoichiometric amount of titanium tetraisoprop oxide and a catalytic amount (20%) of camphorsulfonamide derivatives a s chiral ligands leads to the formation of the corresponding enantioen riched tert-alcohols with enantiomeric ratios up to 94.5 : 5.5. The be st results were obtained when phenones are used as substrates independ ently of the dialkylzinc reagent. The enantioselectivity shows a linea r relationship with the enantiomeric excess of the ligand and seems to be independent of the reaction yield. A tentative catalytic cycle and mechanistic model are proposed for this new reaction. (C) 1998 Elsevi er Science Ltd. All rights reserved.