High enantioselectivities in an (E)-alkene epoxidation by catalytically active chromium salen complexes. Insight into the catalytic cycle.
[structure: see text]. The epoxidation of (E)-beta-methylstyrene mediated by an oxochromium salen complex yields the epoxide in 92% ee in stoichiometric mode, the highest ee yet reported for a metal-mediated epoxidation of an (E)-alkene. The effect of added donor ligands, previously substantial, has reached a ceiling with this complex. In catalytic mode a slightly reduced ee and higher yield is obtained, indicating both the presence of a second oxidation cycle and that the major oxidant reacts with its reduced form.
Chemistry Department and Conway Institute of Biomolecular and Biomedical Sciences, University College Dublin, Belfield, Dublin 4, Ireland.
A M
AM
Daly
M F
MF
Renehan
D G
DG
Gilheany