title: Studies on the Bisoxazoline and (-)-Sparteine Mediated Enantioselective Addition of Organolithium Reagents to Imines.
abstract: The enantioselective addition of organolithium reagents to N-anisyl aldimines promoted by chiral bisoxazolines and (-)-sparteine as external ligands is described. This reaction proceeds readily with a wide range of aldimine substrates (aliphatic, aromatic, olefinic) and organolithium nucleophiles (Me, n-Bu, Ph, vinyl) in excellent yields (81-99%) and with high enantioselectivities (up to 95.5:4.5 er). The external ligands can be used in substoichiometric amounts albeit with slightly attenuated enantioselectivities. A systematic evaluation of the structural features of the bisoxazolines revealed a primary contribution from the substituent at C(4) and a secondary influence from the bridging substituents. A computational analysis (PM3) provided a clear rationalization for the origin of enantioselectivity.
authors.affiliation: Roger Adams Laboratory, Department of Chemistry, University of Illinois Urbana, IL 61801.
authors.forename: Scott E
authors.initials: SE
authors.lastname: Denmark
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Nakajima
authors.forename: Cory M
authors.initials: CM
authors.lastname: Stiff
authors.forename: Olivier J-C
authors.initials: OJ
authors.lastname: Nicaise
authors.forename: Michael
authors.initials: M
authors.lastname: Kranz