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Epoxidation with dioxiranes refers to the synthesis of epoxides from alkenes using three-membered cyclic peroxides, also known as dioxiranes.〔Adam, W.; Saha-Moller, C.; Zhao, C.-G. ''Org. React.'' 2003, ''61'', 219. 〕 Dioxiranes are three-membered cyclic peroxides containing a weak oxygen-oxygen bond. Although they are able to effect oxidations of heteroatom functionality and even carbon-hydrogen bonds,〔Adam, W.; Zhao, C.-G.; Jakka, K. ''Org. React.'' 2007, ''69'', 1.〕 they are most widely used as epoxidizing agents of alkenes. Dioxiranes are electrophilic oxidants that react more quickly with electron-rich than electron-poor double bonds; however, both classes of substrates can be epoxidized within a reasonable time frame. Dioxiranes may be prepared and isolated or generated ''in situ'' from ketones and potassium peroxymonosulfate (Oxone). ''In situ'' preparations may be catalytic in ketone, and if the ketone is chiral, enantioselective epoxidation takes place. The functional group compatibility of dioxiranes is limited somewhat, as side oxidations of amines and sulfides are rapid. Nonetheless, protocols for dioxirane oxidations are entirely metal free. The most common dioxiranes employed for synthesis are dimethyl dioxirane (DMD) and methyl(trifluoromethyl)dioxirane (TFD). :File:DOEpoxGen.png ==Mechanism and stereochemistry== The mechanism of epoxidation with dioxiranes most likely involves concerted oxygen transfer through a spiro transition state.〔Houk, K. N.; Liu, J.; DeMello, N. C.; Condroski, K. R. ''J. Am. Chem. Soc.'' 1997, ''119'', 10147.〕 As oxygen transfer occurs, the plane of the oxirane is perpendicular to and bisects the plane of the alkene pi system. The configuration of the alkene is maintained in the product, ruling out long-lived radical intermediates. In addition, the spiro transition state has been used to explain the sense of selectivity in enantioselective epoxidations with chiral ketones.〔Wang, Z.-X.; Tu, Y.; Frohn, M.; Zhang, J.-R.; Shi, Y. ''J. Am. Chem. Soc.'' 1997, ''119'', 11224.〕 :File:DOEpoxMech.png 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Epoxidation with dioxiranes」の詳細全文を読む スポンサード リンク
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