Dimethyldioxirane , epoxidation

Dimethyl-1,2-dioxetanone, chemiluminescence quantum yield, 1226-7 Dimethyldioxirane epoxidation atkenes, 37-44 deuteriation, 1143 O NMR spectroscopy, 184-5 preparation, 26, 1130-2 structure, 26... 

Billups et al. have reported the synthesis of the first two triscycloproparenes using bromochlorocy-clopropene (Section II.E.2)318, Ag(I) catalysed cycloproparene dimerizations (Section V.B.l)319, and the addition of 11 to Cm via (T-bond opening (Section V.B.3)320. Dimethyldioxirane epoxidation of 96c has provided the first oxaspiropentene derivative—the naphtho analogue of 138 (Section VI.B.2)321. 

Chiral Auxiliary-hased Epoxidation of Substituted Alkenes. High diastereoselectivities were found for the m-CPBA or dimethyldioxirane epoxidation of chiral oxazolidine-substituted alkenes bearing a strongly basic urea group (eq 29). However, in most cases, the diastereoselectivities were superior with dimethyldioxirane. 

The first total synthesis of staurosporine and of e/it-staurosporine has been reported in full (see Vol. 29, p. 378). The glycal-derived epoxide 191 (from dimethyldioxirane epoxidation of the precursor glycal) was treated with the sodium salt of 190 and the product, 192, was then elaborated using iodoamina-tion as the the key cyclization step, radical deiodination then affording 193, an intermediate for synthesis of e r-staurosporine. ... 

In general, peroxomonosulfates have fewer uses in organic chemistry than peroxodisulfates. However, the triple salt is used for oxidizing ketones (qv) to dioxiranes (7) (71,72), which in turn are useful oxidants in organic chemistry. Acetone in water is oxidized by triple salt to dimethyldioxirane, which in turn oxidizes alkenes to epoxides, polycycHc aromatic hydrocarbons to oxides and diones, amines to nitro compounds, sulfides to sulfoxides, phosphines to phosphine oxides, and alkanes to alcohols or carbonyl compounds. 

Fullerene epoxide, C )0, is formed by the UV irradiation of an oxygenated benzene solution of Cfio The O atom bridges a 6 6 bond of the closed fullerene structure. The same compound is also formed as one of the products of the reaction of Cgo with dimethyldioxirane, Mc2COO (see later). ... 

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-... 

Expedient removal of the volatiles after the epoxidation with dimethyldioxirane is crucial to achieve reproducible yields because the epoxide is extremely water sensitive. 

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... 

Analyze the following data on the product ratios obtained in the epoxidation of 3-substituted cyclohexenes by dimethyldioxirane. What are the principal factors that determine the stereoselectivity ... 

The preparation of 2,3,5-trisubstituted 4,5-dihydrofurans 81 with complete regio-control can be realized by an one-pot transformation involving epoxidation of 2-alkenyl-1,3-dicarbonyls by in situ generated dimethyldioxirane, and is followed by a S-exo-ieX intramolecular nucleophilic cyclization under the same basic condition <00TL10127>. 

Epoxidation of allenes.1 The spirodioxides formed by epoxidation of allenes are unstable to acids, and only hindered ones have been obtained on epoxidation with peracids. They can be obtained, however, in 90-95% yield by epoxidation of allenes (even monosubstituted ones) with dimethyldioxirane in acetone buffered with solid K2C03. 

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. 

Epoxidation of amidoallenes with dimethyldioxirane leads to allene oxides as reactive intermediates which can be trapped with dienes in a [4+ 3]-cycloaddition reaction. Exposure of a mixture of amidoallene 177 with cydopentadiene to a small excess of dimethyldioxirane at -45 °C produced endo-bicydooctanone 178 in 60% yield (Eq. 13.60) [69]. The allene oxide is electrophilic, since no reaction takes place with methyl acrylate. 

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. 

Peroxynitrous acid, which has an estimated lifetime of 1-3 s at neutral pH, has been studied through ab initio calculations that suggest that peroxynitrous acid, per-oxyformic acid, and dimethyldioxirane have, despite diverse 0—0 bond energies, similar activation energies for oxygen-atom transfer." The transition-state structures for the epoxidation of ethene and propene with peroxynitrous acid are symmetrical with equal or almost equal bond distances between the spiro oxygen and the carbons of the double bond. 

Two extreme epoxidation modes, spiro and planar, are shown in Fig. 9 [33, 34, 53, 54, 76-85]. Baumstark and coworkers had observed that the epoxidation of cis-hexene of dimethyldioxirane was seven to nine times faster than the corresponding epoxidation of tran.y-hexene [79, 80]. The relative rates of the epoxidation of cisitrans olefins suggest that spiro transition state is favored over planar. In spiro transition states, the steric interaction for cw-olefm is smaller than the steric interaction for fran -olefm. In planar transition states, similar steric interactions would be expected for both cis- and trans-olefms. Computational studies also showed that the spiro transition state is the optimal transition state for oxygen atom transfer from dimethyldioxirane to ethylene, presumably due to the stabilizing interactions... 

All attempts to achieve a direct transformation of the carbazomadurins A (253) and B (254), as well as the disilyl-protected carbazomadurins A (769a) and B (769b), into the epocarbazolins A (258) and B (259) were unsuccessful and resulted in complete decomposition. Therefore, prior to the epoxidation, the disilyl-protected carbazomadurins A (769a) and B (769b) were transformed to the corresponding trisilyl-protected carbazomadurins A (770) and B (771) by treatment with TPS chloride in the presence of stoichiometric amounts of 4-(dimethylamino)pyridine (DMAP). Epoxidation of the fully protected carbazomadurins A (770) and B (771) with dimethyldioxirane at — 20°C, followed by desilylation, provided racemic epocarbazolin A (258) and epocarbazolin B (259) (605) (Scheme 5.82). 

CgoO (1) can also be prepared by allowing toluene solutions of CgQ to react with dimethyldioxirane (Scheme 8.3) [28], The so-obtained product is identical to that prepared by photochemical epoxidation [15], Upon treatment of CgQ with dimethyldioxirane, a second product is formed simultaneously (Scheme 8.3), which was identified to be the 1,3-dioxolane 6. Upon heating 6 in toluene for 24 h at 110 °C, no decomposition could be observed by HPLC, implying that 1 and 6 are formed by different pathways. Replacement of dimethyldioxirane with the more reactive methyl(trifluoromethyl)dioxirane allows much milder reaction conditions [29]. At 0 °C and a reaction time of only some minutes this reaction renders a CgQ conversion rate of more than 90% and higher yields for CgoO as well as for the higher oxides. 

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