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Epoxidation reactions have been established as an important method for the formation of carbon-oxygen bonds. In 1980 Sharpless and Katsuki developed an enantioselective variant for allylic alcohols which is still one of the most elegant methods in asymmetric synthesis. ['] Over the last few years unfunctionalized olefins have also become the focal point of interest as substrates, yielding epoxides in high enantiomeric excess when the optically active (salen)manganese(III) complexes 1 designed by
Jacobsen and Katsuki are used."] The best selectivities are achieved with cis-alkenes; however, recently the epoxidation of olefins having tri-and tetrasubstituted double bonds has also been successful with enantiomeric excesses of over The oxidants of choice are iodosobenzene and sodium hypochlorite at room temperature as well as meta-chloroperbenzoic acid at -78 "C. The proposed mechanism of the Jacobsen-Katsuki epoxidation is based on investigations by Kochi et al. with achiral salen ligands, where the MnV-oxo complexes 2 are postulated to be the catalytically active species (Scheme 1) .I4] L 1 L 2 Scheme 1. Formation of Mnv-oxo complexes 2 in the Jacobsen-Katsuki epoxidation. Ox = oxidant, L = counterion or amine N-oxide ligand.
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## Abstract magnified image In 1,1,1,2,3,4,4,5,5,5‐Decafluoropentane using 2‐phenylpyridine __N‐__oxide as donor ligand, the enantioselectivity of the __Jacobsen–Katsuki__ epoxidation is improved up to 10% ee as compared to established protocols.
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## Abstract Review: 25 refs.