Ethers dimethyldioxirane

This ether, developed for the protection of a pyranoside anomeric hydroxyl, is prepared via a Konigs-Knorr reaction from the glycosyl bromide and 2-(ben-zylthio)ethanol in the presence of DIPEA. It is cleaved, after oxidation with dimethyldioxirane, by treatment with LDA or MeONa. ... 

Dimethyldioxirane, acetone, 48 h, rt, 85-93% yield. p-Bromo-, p-cyano- and 2-naphthylmethyl ethers, and benzylidene acetals can also be deprotected. 

Dimethyldioxirane, acetone, CH2CI2, 0°, 24 h, > 95% yield. Ethers are also oxidized under these conditions. 

Dimethyldioxirane DMDO discovered by Murray and coworkers, is a superior choice for the epoxidation of most olefins, giving comparable or higher yields than m-CPBA-based epoxidation [21]. Proceeding rapidly under neutral and mild conditions, it is especially well suited for the synthesis of sensitive epoxides of enol esters, enol lactones [22], and enol ethers [23]. The reaction is stereospecific, gen-... 

The galactosyl glycal 72 was bound to solid phase via a silyl ether linker. Epoxidation of the glycal using 2,2-dimethyldioxirane and subsequent electrophilic activation of the epoxide resulted in the glycosylation of 3,4-di-O-benzyl glucal 73. After acetylation of the product, the polymer-linked trisaccharide 74 was obtained. 

The reaction of allenes with peracids and other oxygen transfer reagents such as dimethyldioxirane (DM DO) or hydrogen peroxide proceeds via allene oxide intermediates (Scheme 17.17). The allene oxide moiety is a versatile functionality. It encompasses the structural features of an epoxide, an olefin and an enol ether. These reactive intermediates may then isomerize to cyclopropanones, react with nucleophiles to give functionalized ketones or participate in a second epoxidation reaction to give spirodioxides, which can react further with a nucleophile to give hydroxy ketones. 

Epoxides of enol silyl ethers or acetates can be obtained in high yield by reactions with dimethyldioxirane at low temperatures.3 Dimethyldioxirane is generally... 

Activation of 26 with AgBF, led to the intermediate 1,2-A-sulfonylaziridinc, which reacted with the tributyltin ether glycal 27 to afford the dimer 28. The second glycal was activated with dimethyldioxirane (DMDO) to supply the intermediate epoxide that was treated with ZnCl2 and allyl alcohol to afford compound 29. 

Reagents which effect epoxidation of the enol ether unsaturation effect a-hydroxylation comparable to the peracid approach. Thus a combination of molybdenum hexacarbonyl and r-butyl hydroperoxide converts the substrates to a-silyloxy derivatives. The peroxide generate in situ from benzonitrile, potassium carbonate and hydrogen peroxide can also perform the oxidation. Molybdenum-peroxy complexes, including MoOPH, could presumably also effect this transformation. Lastly, dimethyldioxirane has been used to epoxidize alkenes and it is likely that application of this useful, debris free, organic peroxide to these reactions will soon emerge. 

Epoxidations. Formation of chiral epoxides from enol ethers derived from protected glucopyranosyl derivatives has been reported. 1,2-Epoxyalkylphosphonates are obtained from epoxidation of vinylphosphonates. Generation of dimethyldioxirane at high pH (10.5-11.5) is advantageous. ... 

Excellent reviews on dioxirane-mediated oxidations have appeared. One of the most eharacteristic points is that dioxiranes can be applied to the epoxidation of labile olefins such as enol ethers, enol acrylates, allenes and others. Dioxiranes have also been utilized for phenolic oxidation, but in relatively rare cases. Oxidation of simple phenols and anisoles with dimethyldioxirane (544) provided only a complex mixture, so that hindered phenols are more favorable. On treatment with dimethyldioxirane (4 equiv.) in acetone, 2,4-di(terf-butyl)phenol (216) was oxidized to afford in 79% yield the corresponding o-benzoquinone 220, which reacted with 544 and aq. NaHS03 to give catechol 545. Dimethyldioxirane-promoted oxidation of 545 provided again a quantitative yield of 220. Further oxidation of 220 produced a 52% yield of two epoxides 546 and 547 in a ratio of 1 20. Oxidation of thymol (548) was effected with dimethyldioxirane in acetone to afford fhe four oxidation producfs 549-552 in 10, 20, 10 and 10% yields, respectively (Scheme 102). ... 

Dimethyldioxirane, acetone, CH2CI2, 0°C, 24h, >95% yield." Although ketone dioxolanes are cleaved to ketones, aldehyde dimethyl acetals will gives the ester, but the generahty of the later process has not been established beyond the acetal of benzaldehyde. Ethers are also oxidized under these conditions. 

While ethers react only slowly with dimethyldioxirane, they are efficiently hydroxylated by methyl(trifluoromethyl)dioxirane even at low temperatures. Thus r-butyl methyl ether [32] was converted to f-butyl alcohol through its hemiacetal. On the other hand, tetrahydrofuran gave butyrolactone [32] in which presumably the intermediary cyclic hemiacetal was oxidized to the lactone by an additional C —H insertion. The ketal was degraded into 2-butanone and the orthoformate into diethyl carbonate [32]. The latter transformation may serve useful for deketalation under neutral conditions. 

The cnol ether 4 was also converted into the pheromone (7) of the olive fruit fly by reaction with dimethyldioxirane to provide a very unstable epoxide that rearranges to the ketone 6 on treatment with CSA. Reduction of 6 with NaBH4/CcCl1 provides the pheromone 7 as a 13 1 mixture of epimers. 

It is also possible to oxygenate an enolate to give the corresponding acyloin (an a-hydroxy ketone) or alkoxy derivative. Reaction of an enolate anion with oxygen and trimethylphosphite [(MeO)3P], for example, gives an a-hydroxy derivative. 3 Reaction of an enol ether such as 105 with 3,3-dimethyldioxirane leads to the protected a-hydroxy ketone (106), in an example taken from Danishefsky s synthesis of myrocin An effective oxygenation reagent for enolate anions is MoOPh, and a typical use is taken from work by Vedejs to... 

Oxidative debenzylation using dimethyldioxirane proceeds well with benzyl ethers of primary and secondary alcohols and the method is compatible with silyl ethers. Isopropylidene acetals are stable but benzylidene acetals are cleaved. The deprotection of p-bromo. p-cyano and 2-naphthylmethyl ethers can also be accomplished. 

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