Dioxiranes dimethyldioxirane

A theoretical study on the oxidation of methane, propane and isobutane with dioxirane, dimethyldioxirane, difluorodioxirane and methyl(trifluoromethyl)di-oxirane has provided a rational for the formation of radical intermediales when dioxygen is rigorously excluded and supported the generally accepted, highly exothermic, concerted oxygen insertion mechanism for the oxidation under typical preparative conditions. The activation barriers for the oxidation of methane (44.2), propane (30.3) and isohutane (22.4 kcal mol" ) with dimethyldioxirane have been evaluated [48e]. Perfluorodialkyloxaziridines are also mild and selective reagents for the hydroxylation of alkanes [49] ... 

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. 

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... 

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. 

FIGURE 13. B3LYP/6-311- -G(3df,2p)-optimized stractures of dioxirane (DO), dimethyldioxirane (DMDO) and methyl(trifluoromethyl)dioxirane (TFDO). Bold numbers for DO are experimental microwave-stractural data. ... 

The transition structures for the epoxidation of ethylene and propylene with peroxyformic acid and of ethylene with dioxirane and dimethyldioxirane calculated at the B3LYP, QCISD and CCSD levels are symmetrical with a spiro orientation of the electrophilic oxygen, whereas the MP2 calculations favor unsymmetrical transition structures. The geometries of the transition structures calculated using the B3LYP functional are close to those found at QCISD, CCSD, CCSD(T) levels as well as those found at the CASSCF(10,9) and CASSCF(10,10) levels for the transition structure of the epoxidation of ethylene. 

In summary, transition structures with dioxirane and dimethyldioxirane are unsymmet-rical at the MP2/6-31G level, but are symmetrical at the QCISD/6-31G and B3LYP/6-31G levels. The transition states for oxidation of ethylene by carbonyl oxides do not suffer from the same difficulties as those for dioxirane and peroxyforaiic acid. Even at the MP2/6-31G level, they are symmetrical (Figure 17). The barriers at the MP2 and MP4 levels are similar and solvent has relatively little effect. The calculated barriers agree well with experiment . In a similar fashion, the oxidation of ethylene by peroxyformic acid has been studied at the MP2/6-31G, MP4/6-31G, QCISD/6-31G and CCSD(T)/6-31G and B3LYP levels of theory. The MP2/6-31G level of theory calculations lead to an unsymmetrical transition structure for peracid epoxidation that, as noted above, is an artifact of the method. However, QCISD/6-31G and B3LYP/6-31G calculations both result in symmetrical transition structures with essentially equal C—O bonds. 

The NMR data of dimethyldioxirane 36 have already been reviewed, but the closely related spectrum of methyl(trifluoromethyl)dioxirane 37 was not reviewed and a comparison of its experimental data with the computed values for the parent dioxirane 38 and of difluorodioxirane 39 can be of interest. Experimental and computed data are gathered in Table 9. 

Dioxirane chemistry is well documented . Extensive kinetic, stereochemical and 0-labeling data suggested that dimethyldioxirane is the oxygen-atom transfer reagent in the Oxone-acetone system . Murray and Jeyaraman have shown that dialkyl dioxiranes can be isolated by low-temperature distillation from the reaction mixture of oxone and ketone . 

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. 

Solutions of isolated dioxiranes, characteristically dimethyldioxirane (DMD) in acetone, possess a pale yellow color, which serves as a convenient analytical index for monitoring the dioxirane consumption in oxidation reactions and kinetic studies. For DMD, the absorption maximum (n-jt transition ) centers at ca 325 nm, with a molar extinction coefficient (e) of 12.5 0.5 M cm in acetone. The alternative and more rigorous analytical method for dioxirane quantification utilizes iodometry (Kl/starch). 

Two new reactive, very powerful organic peroxides, dimethyldioxirane and methyl(trifluoromethyl)dioxirane (4), have been introduced.81-83 The latter is more reactive and can be used more conveniently.84 85 Acyclic alkanes give a mixture of isomeric ketones on oxidation with methyl(trifluoromethyl)dioxirane,84,85 while cyclohexanone is the sole product in the oxidation of cyclohexane (99% selectivity at 98% conversion).85 With the exception of norbomane, which undergoes oxidation at the secondary C-2 position, highly selective tertiary hydroxylations can be carried out with regioselectivities in the same order of magnitude as in oxidations by peracids.85-87 A similar mild and selective tertiary hydroxylation by perfluorodialkyloxaziridines was also reported.88 Oxidation with dioxiranes is highly stereoselective 85... 

To a methyl ethyl ketone solution of =Si—H containing polymers or copolymers, a cold solution (ca. -10 °C) of dimethyldioxirane in acetone was quickly added and reacted for 30 min at 0 °C. The mole ratio of dioxirane to polymer was ca. 1.2 1.3. The resulting silanol polymers or copolymers were obtained either in solution or precipitated into hexanes followed by vacuum dry at 40 °C for 24 h. 

Dioxiranes constitute a new class of organic peroxides that possess great potential as oxidants with a variety of applications in synthetic organic chemistry.5 7 A new convenient route for the synthesis of silanol polymers has been developed by the selective oxidation of =Si—H bonds with dimethyldioxirane. A series of styrene-based silanol polymers and copolymers were synthesized (Scheme l).8 9 The precursor polymers and styrene copolymers containing =Si—H bond were first synthesized by free radical polymerization of the corresponding monomers or copolymerization of the... 

Dimethyldioxirane oxidizes acyclic vinylsilanes at room temperature to the corresponding epoxides 166 in excellent yield (equation 141)255. Allylic oxidation is found in appreciable amounts when cyclic vinylsilanes are used. It is interesting to note that simple alkenes react faster with dioxirane than vinylsilanes. The trend appears to be reversed when MCPBA is employed as the oxidant. 

Dimethyldioxirane has also been used as the epoxidizing agent in a key step in the synthesis of A-norsteroids69,70. The reaction occurs in dichloromethane-acetone and is highly regio- and stereoselective as shown in equation 9. Dioxiranes may also be generated in situ, by reaction of potassium monoperoxysulfate (sold commercially as OXONE) and cyclohexanones. In this case, cyclohexene derivatives may be smoothly epoxidized in 40-100% yields (equation 10)71. 

Electronic and steric effects in the epoxidation of alkenes by dimethyldioxirane have been investigated313. Both mechanistic and synthetic aspects of the chemistry of dioxiranes have been reviewed314,315. 

Dimethyldioxirane (7) and methyl(trifluoromethyl)dioxirane (8) are the two most effective reagents mainly used in preparative organic chemistry. 

AMI and PM3 calculations reveal that epoxidations by DMDO and TFDO involve peroxide-bond cr at a very early stage and that TFDO is the most reactive dioxirane as the CF3 group in it stabilizes this cr level. In accord with previous calculations a spiro transition state is predicted. Furthermore, allene is predicted to be less reactive than alkenes toward epoxidation by DMDO.192 DFT calculations on the oxidation of primary amines by dimethyldioxirane predict a late transition state with a barrier of 17.7 kcal mol-1 which is drastically lowered by hydrogen bonding to the O—O bond to just 1.3 kcal mol-1 in protic solvents.193... 

Bis (trifluoromethy l)dioxirane See Dimethyldioxirane See other CYCLIC PEROXIDES... 

Dioxiranes (32) are isomeric with carbonyl oxides (33), one of the peroxidic intermediates involved in the ozonolysis process.9 Dimethyldioxirane (DMDO) (31) epoxidizes the double bond of the protected galactal favoring the Oepoxide 8 with a selectivity of 20 1.10,11 You can use 31 likewise to transform an aldehyde into a carboxylic acid. 

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