title: C-selective and diastereoselective alkyl addition to β,γ-alkynyl-α-imino esters with zinc(II)ate complexes.
abstract: Since umpolung α-imino esters contain three electrophilic centers, regioselective alkyl addition with traditional organometallic reagents has been a serious problem in the practical synthesis of versatile chiral α-amino acid derivatives. An unusual C-alkyl addition to α-imino esters using a Grignard reagent (RMgX)-derived zinc(II)ate was developed. Zinc(II)ate complexes consist of a Lewis acidic [MgX](+) moiety, a nucleophilic [R3 Zn](-) moiety, and 2 [MgX2 ]. Therefore, the ionically separated [R3 Zn](-) selectively attacks the imino carbon atom ,which is most strongly activated by chelation of [MgX](+) . In particular, chiral β,γ-alkynyl-α-imino esters can strongly promote highly regio- and diastereoselective C-alkylation because of structural considerations, and the corresponding optically active α-quaternary amino acid derivatives are obtained within 5 minutes in high to excellent yields.
authors.affiliation: Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa, Nagoya 464-8603 (Japan) http://www.ishihara-lab.net/
authors.forename: Manabu
authors.initials: M
authors.lastname: Hatano
authors.forename: Kenji
authors.initials: K
authors.lastname: Yamashita
authors.forename: Mai
authors.initials: M
authors.lastname: Mizuno
authors.forename: Orie
authors.initials: O
authors.lastname: Ito
authors.forename: Kazuaki
authors.initials: K
authors.lastname: Ishihara
keywords: Grignard reagents; alkylation; regioselectivity; synthetic methods; zinc