title: Mechanistic insight into stereoselective carbolithiation.
abstract: This article addresses the mechanistic features of asymmetric carbolithiation of β-methylstyrenes. While often the presence of functional groups is required to obtain high enantioselectivities in carbolithiation reactions, simple β-methylstyrene also gives high selectivities in (-)-sparteine-mediated addition of alkyl lithium compounds. Computational studies on the carbolithiation of β-methylstyrene with (-)-sparteine show that the observed selectivities are the result of repulsion effects in the diastereomeric transition states between the (-)-sparteine⋅alkyl lithium adduct and the β-methylstyrene, upon approximation of the two reactants. In contrast, for the ortho-amino β-methylstyrene (E)-benzyl(2-propenylphenyl)amine (4) X-ray structure analyses of intermediate lithium amides indicate a carbolithiation mechanism in which one side of the double bond is shielded by the amide moiety, leaving only one side free for approach of the chiral alkyl lithium adduct.
authors.affiliation: Anorganische Chemie, Technische Universität Dortmund, Otto-Hahn-Strasse 6, 44227 Dortmund, Germany.
authors.forename: Viktoria H
authors.initials: VH
authors.lastname: Gessner
authors.forename: Stephan G
authors.initials: SG
authors.lastname: Koller
authors.forename: Carsten
authors.initials: C
authors.lastname: Strohmann
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Hogan
authors.forename: Donal F
authors.initials: DF
authors.lastname: O'Shea