Dioxirane derivatives

Epoxidation by Dioxirane Derivatives. Another useful epoxidizing agent is dimethyldioxirane (DMDO),86 which is generated by in situ reaction of acetone and peroxymonosulfate in buffered aqueous solution. Distillation gives about aO.lM solution of DMDO in acetone.87... 

The similarity of olefin epoxidation by TM peroxo and hydroperoxo complexes with epoxidation by dioxirane derivatives R2CO2 and percar-boxylic acids RCO(OOH) was confirmed by computational studies [73-79]. This similarity holds in particular for the spiro-type transition structure. 

Shi and coworkers developed a method using silyl enol ethers and in situ generated chiral dioxirane derivatives. Lopp and coworkers could develop an asymmetric dihydroxy lation method for racemic 2-hydroxymethyl ketones 202a-c, using TBHP as oxygen source in combination with the Sharpless catalytic system Ti(OPr-i)4/DET, yielding... 

The synthetically most useful method for the preparation of dioxiranes is the reaction of appropriate ketones (acetone, trill uoroacetone, 2-butanone, cyclohexanone etc.) with Caroate, commercially available as the triple salt of potassium monoperoxysul-fate (KHSOs). The catalytic cycle of the dioxirane formation and oxidation is shown in Scheme 1 in general form. For acetone as the ketone, by simple distillation at a slightly reduced pressure ca 100 torr) at room temperature ca 20 °C), Jeyaraman and Murray successfully isolated dimethyldioxirane (DMD) as a pale yellow solution in acetone (maximally ca 0.1 M). This pivotal achievement in 1985 fomented the subsequent intensive research activity in dioxirane chemistry, mainly the synthetic applications but also the mechanistic and theoretical aspects. The more reactive (up to a thousandfold ) fluorinated dioxirane, methyl(trifluoromethyl)dioxirane (TFD), was later isolated in a similar manner by Curd, Mello and coworkers". For dioxirane derived from less volatile ketones, e.g. cyclohexanone, the salting-out technique has been developed by Murray and coworkers to obtain the corresponding dioxirane solution. 

Chiral dioxiranes continue to be examined for the synthesis of enantioenriched epoxides. An interesting report details the use of a dioxirane derived from oxazolidinone 7 for the... 

Recently, Wong and Shi have examined the effect of substitution in the 6- or 8-position in the asymmetric epoxidation of chromenes by chiral dioxiranes derived from ketones 52 and 53. Up to 93% ee was achieved, with higher ee s obtained when substrates are substituted at the 6-position <2006JOC3973>. 

NMR spectra of dioxiranes derived from fluorinated acetophenones 29-36 using Oxone have also been reported <20030L2853>. The fluorine nuclei of CF3 group bonded to dioxirane ring typically resonates at —85 0.5 ppm. 

They found that the erythrolthreo-% i,cX N Xtj is X-substituent dependent, acting through H-bonding, which was demonstrated by the TFDO Ic epoxidation of 73. An example of cyclohexene epoxidation by dioxiranes derived from various ketones grafted on solid supports has also appeared <1996MI273>. Shi and co-workers reported <1996JA9806> excellent ee s of asymmetric epoxidation of different /ra t-olefms by fructose-derived ketones 74 before then, only low enantioselectivities (9-20%) have been reported on this type of reaction. 

Solladie-Cavallo, A., Lupattelli, P., Jierry, L., Bovicelli, P., Angeli, F., Antonioletti, R., Klein, A. Asymmetric oxidation of silyl enol ethers using chiral dioxiranes derived from a-fluoro cyclohexanones. Tetrahedron Lett. 2003,44, 6523-6526. 

Epoxidations. Further utilities for the dioxirane derived from fructose is the regio-and enantioselective epoxidation of conjugated dienes and enynes. Continuing explorations of the (salen)manganese(III) systems have uncovered the catalyzed epoxidation of 2-sulfonyl-1,3-dienes at the nondeactivated sites, and the advantage of added carboxylate salt as cocatalyst. ... 

Stereoselective epoxidations of substituted cyclohexenes with in situ generated dioxiranes have been studied <94TL1577>. The most favorable trans/cis selectivities have been achieved using dioxiranes derived from sterically hindered ketones (Scheme 26). 

Dioxiranes derived from chiral ketones have been used extensively to promote the enantioselective epoxidahon of alkenes [60]. The first examples of immobilized chiral ketones for this reaction were reported by Sartori and Armstrong [61]. A modified racemic hopinone was supported onto amorphous sihca KG-60, mesoporous silica MGM-41, and 2% crosslinked PS, respechvely, to obtain the insoluble precatalysts 38a-c (Scheme 8.18). 

In an attempt to determine the atmospheric oxidation processes that would result in an arene oxide functional group in PAHs, Murray and Kong (1994) studied the reaction of particle-bound PAHs with oxidants derived from the reactions of ozone with alkenes. Phenanthrene and pyrene were converted to arene oxides under these simulated atmospheric conditions. Control experiments indicated that the oxidant responsible for the transformation was not ozone, but a product of the reaction of ozone with tetramethylethylene (TME), probably the carbonyl oxide or the dioxirane derived from TME. 

A fluorous medium has been utilized for alkcnc epoxidation employing the dioxirane derived from the fluoroketone 14, which is also effective in catalytic quantities with Oxone as the terminal oxidant. For example, treatment of tro w-4-decene (13) with 5 mol% of ketone 14 and 1.5 equiv of Oxone in a bicarbonate buffered water exanuoroisopropanol (HFIP) medium led to the quantitative formation of the corre.sponding epoxide 15 <01TL4463>. 

Ketones and Other Oxygen Functions. Various ketones can be converted to the corresponding dioxiranes by treatment with buffered aqueous solutions of Oxone (eq 1). Of particular interest are dimethyldioxirane (R = R = Me) and methyl(trifluoro-methyl)dioxirane (R = Me, R = CF3) derived from acetone and l,l,l-trifluoro-2-propanone, respectively. The discovery of a method for the isolation of dilute solutions of these volatile dioxiranes in the parent ketone by codistillation from the reaction mixture has opened an exciting new area of oxidation chemistry. Solutions of dioxiranes derived from higher molecular weight ketones have also been prepared. ... 

Dioxirans derived from hexitols and tetritols have been used as cross-linking reagents for DNA. ... 

The stereochemistry of epoxides generated by chiral dioxiranes provides the opportunity to further address the transition state. The dioxirane derived from 39 has two diastereomeric oxygens. The equatorial oxygen is likely to be sterically more accessible for the epoxidation. Our studies show that while the epoxidation of trans- and tri-substitued olefins with ketone 39 proceeds mainly through spiro A, planar B is also competing (Figure 3.5) [34, 35, 43-47, 49, 50, 59]. Spiro A and planar B give the opposite stereochemistry for the epoxide product, thus their competition will affect the ee obtained for epoxidation. Studies have shown that the extent of involvement of... 

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