ENANTIOSELECTIVE CATALYSIS .14. ASYMMETRIC GRIGNARD CROSS-COUPLING REACTION - AN INVESTIGATION OF THE FACTORS INFLUENCING ASYMMETRIC INDUCTION WITH A NEW-TYPE OF PYRROLIDINEPHOSPHANE

An investigation of the asymmetric synthesis of 3-phenyl-1-butene by t he Grignard cross-coupling reaction is presented. The reaction is cata lysed by nickel complexes of bisphosphane and 3-diphenylphosphanylpyrr olidine-type ligands. A comparison of the results obtained with our P, N monophosphane ligands with those obtained with the most effective kn own amino acid derived P,N ligands shows a similar enantioselectivity but an inverse sense of optical induction. An Xray structural analysis of the 1-phenylethyl Grignard compound is reported. Quantitative anal ysis and the determination of enantiomeric composition of the catalyti c samples is accomplished using a novel enantioselective GLC separatio n. Compared to the popular model reaction that uses a chloride-contain ing Grignard compound and vinyl bromide as starting compounds, we obta in improved enantioselectivities of P,N monophosphane catalysts by sub stituting vinyl bromide with vinyl chloride. With two of the new P,N l igands we find a nonlinear dependence of enantioselectivity on the ena nliomeric purity of the ligands (asymmetric amplification). Catalytic results subject to such nonlinear effects show a dependence on the lig and to nickel ratio.