Epoxidations using peroxygens

The —N=C— bond in imines, especially Schiff bases formed from aromatic aldehydes and amines, can be epoxidized by peracids to form oxaziridines [N(0)C].326 Unlike epoxides, oxaziridines will oxygen-transfer.327 Chiral oxaziridines have been used to carry out enantioselective epoxidations,328 although these compounds are often prepared by non-peroxygen routes.329 Oxaziridines can also be rearranged to oximes or nitrones (Figure 3.85).330... 

The most widely accepted method for epoxidation of alkenes remains oxidation with organic peracids. The early work (up to 1970) in this field shows that a large number of dienes and polyenes were oxidized in this manner . The most commonly used peracids are peracetic, monoperphthalic and perbenzoic acids which are most dominant in industrial applications. On the other hand, in laboratory procedures m-chloroperbenzoic acid, MCPBA, is often used, with trifluoroperacetic acid cited in more difficult transformations. Recently, the transportation of m-chloroperbenzoic acid has been restricted and the use of other peroxygen agents has been gaining acceptance as a general alternative. Among the substrate types epoxidized it would be especially worthy to point out polyunsaturated... 

If substituents on the sulphur are more electron-withdrawing, or to obtain faster reaction, activated peroxygen systems can be used to make sulphoxides, overoxidation to sulphones being minimised simply by controlling temperature and addition rate, at the correct molar ratio. Examples include H2O2 catalysed by tungsten(VI), vanadium(V) [213], molybdenum(VI) [214], or selenium(IV) [215], and peracetic acid (which, as for epoxidations, works better in non-protic media) [216]. Sodium perborate in acetic acid is also effective [217]. 

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