title: Synthesis of Bis(oxazoline) Ligands Possessing C-5 gem-Disubstitution and Their Application in Asymmetric Friedel-Crafts Alkylations.
abstract: A series of eight novel bis(oxazoline) ligands incorporating gem-disubstitution on one of the oxazoline rings were prepared from (S)-valine. These ligands are designed as a cost-effective alternative to similar ligands possessing an oxazolinyl C(5)-tert-butyl group derived from expensive (S)-tert-leucine. Four of the ligands possess a C(4)-gem-dimethyl group and four a C(4)-gem-diphenyl group adjacent to the C(5)-isopropyl substituent. Zinc complexes of ligands 11a-h, along with non-C(4)-gem-disubstituted analogues 1a-g, were effective in the Friedel-Crafts alkylation of both indole (up to 74% ee) and 2-methoxyfuran (up to 95% ee) with a series of nitroalkenes. Three of the ligands (11a-c), an iron dichloride complex of ligand 11d and two zinc dichloride complexes, were characterized by X-ray crystallography, one with ligand 11d and the second a bis-tert-butyl-substituted N-methylamine ligand. A direct comparison of the latter structures clearly illustrates the gem-dimethyl effect.
authors.affiliation: Centre for Synthesis and Chemical Biology, School of Chemistry and Chemical Biology, University College Dublin , Belfield, Dublin 4, Ireland.
authors.forename: Steven
authors.initials: S
authors.lastname: O'Reilly
authors.affiliation: Centre for Synthesis and Chemical Biology, School of Chemistry and Chemical Biology, University College Dublin , Belfield, Dublin 4, Ireland.
authors.forename: Miriam
authors.initials: M
authors.lastname: Aylward
authors.affiliation: Centre for Synthesis and Chemical Biology, School of Chemistry and Chemical Biology, University College Dublin , Belfield, Dublin 4, Ireland.
authors.forename: Caoimhe
authors.initials: C
authors.lastname: Keogh-Hansen
authors.affiliation: Centre for Synthesis and Chemical Biology, School of Chemistry and Chemical Biology, University College Dublin , Belfield, Dublin 4, Ireland.
authors.forename: Brian
authors.initials: B
authors.lastname: Fitzpatrick
authors.affiliation: Centre for Synthesis and Chemical Biology, School of Chemistry and Chemical Biology, University College Dublin , Belfield, Dublin 4, Ireland.
authors.forename: Helen A
authors.initials: HA
authors.lastname: McManus
authors.affiliation: Centre for Synthesis and Chemical Biology, School of Chemistry and Chemical Biology, University College Dublin , Belfield, Dublin 4, Ireland.
authors.forename: Helge
authors.initials: H
authors.lastname: Müller-Bunz
authors.affiliation: Centre for Synthesis and Chemical Biology, School of Chemistry and Chemical Biology, University College Dublin , Belfield, Dublin 4, Ireland.
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Guiry