Asymmetric catalysis with self-organized chiral lanthanum complexes: practical and highly enantioselective epoxidation of alpha,beta-unsaturated ketones |
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Authors: | Daikai Kazuhiro Hayano Tetsuji Kino Rie Furuno Hiroshi Kagawa Takumi Inanaga Junji |
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Institution: | Institute for Fundamental Research of Organic Chemistry, Kyushu University, Fukuoka, Japan. |
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Abstract: | A highly efficient and practical method for obtaining alpha,beta-epoxy ketones with high optical purities was developed. The chiral lanthanum complex self-organized in situ from lanthanum triisopropoxide, (R)-BINOL, triarylphosphine oxide, and alkyl hydroperoxide (1:1:1:1) was found to catalyze the epoxidation of alpha,beta-unsaturated ketones with tert-butyl hydroperoxide or cumene hydroperoxide at room temperature to give the corresponding epoxy ketones in high enantioselectivities (up to >99% enantiomeric excess (ee)). A remarkably high asymmetric amplification, a positive nonlinear effect, was observed in the epoxidation of chalcone, which strongly suggests the formation of a dinuclear peroxide-involved mu-complex as the active catalyst. |
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