Peroxides in epoxidations

R, R -Tartaric (racemic) acid is obtained synthetically by epoxidation of maleic acid with hydrogen peroxide in the presence of a catalyst followed... 

Nucleophilic opening of oxiranes to give ultimately 1,2-diols is usually effected without isolation of the oxirane oxiranation (epoxidation) of alkenes with unbuffered peroxy-ethanoic acid or hydrogen peroxide in methanoic acid (Section 5.05.4.2.2(/)) tends to give monoesters of 1,2-diols (e.g. 53), which can be hydrolyzed to the diols (Scheme 46). 

The reductive elimination of a variety of )3-substituted sulfones for the preparation of di-and tri-substituted olefins (e.g. 75 to 76) and the use of allyl sulfones as synthetic equivalents of the allyl dianion CH=CH—CHj , has prompted considerable interest in the [1,3]rearrangements of allylic sulfones ". Kocienski has thus reported that while epoxidation of allylic sulfone 74 with MCPBA in CH2CI2 at room temperature afforded the expected product 75, epoxidation in the presence of two equivalents of NaHCOj afforded the isomeric j ,y-epoxysulfone 77. Similar results were obtained with other a-mono- or di-substituted sulfones. On the other hand, the reaction of y-substituted allylic sulfones results in the isomerization of the double bond, only. The following addition-elimination free radical chain mechanism has been suggested (equations 45, 46). In a closely related and simultaneously published investigation, Whitham and coworkers reported the 1,3-rearrangement of a number of acyclic and cyclic allylic p-tolyl sulfones on treatment with either benzoyl peroxide in CCI4 under reflux or with... 

Hexafluoroacetone and hydrogen peroxide in buffered aqueous solution can epoxidize alkenes and allylic alcohols.101 N, Af-Dialkylpiperidin-4-one salts are also good catalysts for epoxidation.102 The polar effect of the quaternary nitrogen enhances the... 

Two reagents were investigated as less expensive replacements for MCPBA in the epoxidation of VII (a) 30% hydrogen peroxide in acetic acid at 90-100°C (b) 30% hydrogen peroxide and acetonitrile in ethanol in the presence of potassium bicarbonate (19,20). The first reaction gave a mixture of VIII and an unidentified product. 

Fig. 35 Mechanism of formation of hydrogen peroxide in the Wagnerova Type II photooxygenation of alcohols and its in-situ use to epoxidize alkenes and oxidized sulfides.

In some cases, the pyrrolo[l,2-f]oxazoles were epoxidized with hydrogen peroxide in dichloromethane affording the epoxide with control of stereoselectivity (Equation 52) <1997TA2421, 2000T2437, 2004TA1239>. 

The use of other peroxides in the epoxidation of glycals is limited by selectivities that are often inferior to those achieved with DMDO. One notable exception is the use of the wCPBA (m-chloroperbenzoic acid)/KF combination and its recent successful application in one-pot epoxidation alcoholysis (Scheme 5.66) [197]. This involved treatment of benzylated D-galactal 36 in dichloromethane/methanol with a mixture of wCPBA and KF (2 1) in anhydrous dichloromethane to give methyl-2-hydroxygalactoside 165. 

The highly chemo-, regio-, and diastereoselective and stereospecific epoxidation of various allylic alcohols with only 1 equivalent of hydrogen peroxide in water solvent could be efficiently catalyzed by an isolated dinuclear peroxotungstate [W203(02)4(H20)2]2 [93,94] ... 

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