Enantioselective Grignard-type addition of allyltitanium reagents having the center of chirality at titanium

Article abstract of DOI:10.1021/om00089a020

Addition of allylmagnesium chloride to the chiral and racemic titanium(IV) compound CpCp′Ti(C₆F₅)Cl, in which Cp = η⁵-C₅H₅ and Cp′ = η⁵-C₅H₄C(CH₃)₃, yields CpCp′Ti(C₆F₅)C₃H₅. The latter reacts diastereoselectively with aldehydes to afford adducts of the type CpCp′Ti(C₆F₅)OCHRC₃H₅, diastereomeric excess (de) being 12-40%. Optically active (+)-CpCp′Ti(C₆F₅)Cl was also treated with allylmagnesium chloride, benzaldehyde added, and the adduct hydrolyzed in a one-pot reaction to provide the Grignard-type adduct. Enantiomeric excess (ee) amounts to 11%. Since the de value in the racemic series is 20%, loss of chiral information is occurring, possibly during the addition of allylmagnesium chloride to (+)-CpCp′Ti(C₆F₅)Cl.