title: Asymmetric alkene epoxidation with chromium oxo salen complexes. A systematic study of salen ligand substituents.
abstract: [structure: see text]. In the stoichiometric asymmetric epoxidation of E-beta-methylstyrene with cationic chromium-salen oxo complexes, enantioselectivity is increased by halo-substitution at the 3,3'- and 6,6'-positions and decreased at the 4,4'- and 5,5'-positions on the salen rings. Addition of triphenylphosphine oxide significantly increases selection with 3,3'- or 5,5'-substituents but not with 4,4'- or 6,6'-substituents. Use of nitrate counterion is beneficial in most cases. The results are discussed with respect to the mode of stereoselection in metal-salen epoxidations.
authors.affiliation: Chemistry Department and Conway Institute of Biomolecular and Biomedical Sciences, University College Dublin, Belfield, Dublin 4, Ireland.
authors.forename: C P
authors.initials: CP
authors.lastname: O'Mahony
authors.forename: E M
authors.initials: EM
authors.lastname: McGarrigle
authors.forename: M F
authors.initials: MF
authors.lastname: Renehan
authors.forename: K M
authors.initials: KM
authors.lastname: Ryan
authors.forename: N J
authors.initials: NJ
authors.lastname: Kerrigan
authors.forename: C
authors.initials: C
authors.lastname: Bousquet
authors.forename: D G
authors.initials: DG
authors.lastname: Gilheany