title: Chiral N-heterocyclic carbene ligands bearing a pyridine moiety for the copper-catalyzed alkylation of N-sulfonylimines with dialkylzinc reagents.
abstract: Amino acid-derived chiral imidazolium salts, each bearing a pyridine ring, were developed as N-heterocyclic carbene ligands. The copper-catalyzed asymmetric alkylation of various N-sulfonylimines with dialkylzinc reagents in the presence of these chiral imidazolium salts afforded the corresponding alkylated products with high enantioselectivity (up to 99 % ee). The addition of HMPA to the reaction mixture as a co-solvent is critical in terms of chemical yield and enantioselectivity. A wide range of N-sulfonylimines and dialkylzinc reagents were found to be applicable to this reaction.
authors.affiliation: Division of Material Chemistry, Graduate School of Natural Science and Technology, Kanazawa University, Kakuma, Kanazawa, Ishikawa, 920-1192 (Japan), Fax: (+81) 76-264-5742. soeta@se.kanazawa-u.ac.jp.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Soeta
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Ishizaka
authors.forename: Yuta
authors.initials: Y
authors.lastname: Tabatake
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Ukaji
keywords: N-heterocyclic carbenes; N-sulfonylimines; asymmetric alkylation; copper catalysis; enantioselectivity