Sharpless epoxidation

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The Sharpless epoxidation reaction is an enantioselective chemical reaction to prepare 2,3-epoxyalcohols from primary and secondary allylic alcohols.<ref>Katsuki, T.; Sharpless, K. B. J. Am. Chem. Soc. 1980, 102, 5974. (DOI:10.1021/ja00538a077)</ref><ref>Hill, J. G.; Sharpless, K. B.; Exon, C. M.; Regenye, R. Org. Syn., Coll. Vol. 7, p.461 (1990); Vol. 63, p.66 (1985). (Article)</ref> This reaction gives good yields and enantioselectivities over a broad range of substrates.

Image:Sharpless Asymmetric Epoxidation Scheme.png

The oxidizing agent is t-butylperoxide. Enantioselectivity is achieved by a catalyst formed from titanium tetra(isopropoxide) and diethyl tartrate. Only 5-10 mol% of the catalyst in the presence of 3Å molecular sieves (3Å MS) is necessary.<ref>Gao, Y.; Hanson, R. M.; Klunder, J. M.; Ko, S. Y.; Masamune, H.; Sharpless, K. B. J. Am. Chem. Soc. 1987, 109, 5765-5780. (DOI:10.1021/ja00253a032)</ref>

Several reviews have been published.<ref>Johnson, R. A.; Sharpless, K. B. Comp. Org. Syn. 1991, 7, 389-436. (Review)</ref><ref>Hüft, E. Top. Curr. Chem. 1993, 164, 63-77. (Review)</ref><ref>Katsuki, T.; Martin, V. S. Org. React. 1996, 48, 1-300. (Review)</ref><ref>Pfenninger, A. Synthesis 1986, 89-116. (Review)</ref>

Epoxides can be easily converted into dialcohols, aminoalcohols or ethers, so formation of chiral epoxides is a very important step in the synthesis of natural products. K. Barry Sharpless shared the Nobel prize in 2001 for his work on asymmetric oxidations. The prize was shared with William S. Knowles and Ryoji Noyori.

[edit] Reaction mechanism

The Sharpless group has investigated both the reaction kinetics<ref>Woodard, S. S.; Finn, M. G.; Sharpless, K. B. J. Am. Chem. Soc. 1991, 113, 106-113. (DOI:10.1021/ja00001a018)</ref> and the structure of the catalyst<ref>Finn, M. G.; Sharpless, K. B. J. Am. Chem. Soc. 1991, 113, 113-126. (DOI:10.1021/ja00001a019)</ref>.