Abstract
We have developed a highly efficient and practical method for obtaining α,β-epoxy ketones from the corresponding α,β-unsaturated ketones in excellent enantioselectivities (up to >99% ee), in which a novel chiral lanthanum complex self-organized in situ from lanthanum triisopropoxide, (R)-BINOL, triphenylphosphine oxide, and cumene hydroperoxide (1:1:1:1) is posturated as an active catalyst for the epoxidation. In order to have an insight into the structure of the real catalytic species, the linear/nonlinear effects concerning the relationship between the optical purities of the chiral ligand and those of the epoxide were examined. When the catalysts prepared from variously (R)-enriched BINOLs were used, remarkably high asymmetric amplifications were observed. On the other hand, a linear relationship was obtained in the use of the catalysts prepared by mixing the enantiopure (R)-La complex and (S)-La complex in different ratios. These results in addition to the MALDI-TOF MS analysis of the active catalyst strongly support the speculated dimeric 1:1:1:1 complex with high thermodynamic stability. The epoxy ketones thus obtained were successfully converted to some biologically important synthetic intermediates such as β-hydroxy-α-amino acids, α-amino-β-lactone and 3-hydroxy-γ-lactone in good overall yields and in high optical purities.
