REGIOSELECTIVE AND STEREOSELECTIVE CARBON-CARBON BOND FORMATION THROUGH TRANSITION-METAL CATALYSIS - THE INFLUENCE OF CATALYST CHIRALITY ON SELECTIVE ETHYLMAGNESATION OF CHIRAL, NONRACEMIC ALCOHOLS AND ETHERS

Reaction of chiral zirconium dichloride 1 with EtMgCl leads to the formation of (R)-2. The transition metal-alkene complex 2 may then be employed as an effective catalyst in ethylmagnesations of nonracemic allylic alcohols and ethers. These transformations proceed with varying levels of diastereochemical control, depending on which antipode of the chiral substrate is employed. The difference between the stereo- and regiochemical outcome in reactions catalyzed by the achiral CP2ZrCl2 and 1, the variable sensitivity of these sets of reactions to competing ligating Lewis basic solvents, and the influence of the reaction temperature on the regiochemical outcome of carbometalation is described. These data provide important insights into various mechanistic aspects of the carbomagnesation process.