Oxidation dioxiranes

Several other oxidizing agents can be made from hydrogen peroxide and thus be derived indirectly from oxygen. These include sodium perborate, sodium percarbonate, urea peroxide, peracids, potassium peroxymonosulfate, amine oxides, dioxiranes, and iodosobenzene (4.24). 

Silyl enol ethers are a class of electron-rich, nonaromatic compounds that easily form reactive radical cations on one electron oxidation. The silyl enol ether functional group is closely related to the carbonyl function and consequently, syntheses of silyl enol ethers generally make use of enolates. In addition, silyl enol ethers can be described as masked enols or enolates since their reactions often yield ketones. A number of oxidation reactions of silyl enol ethers making use of oxygen or oxygen-containing reagents such as peroxides, peracids (known as Rubottom oxidation), dioxirane, osmium tetraoxide, or triphenyl phosphite ozonide have been described in the literature. In all cases either a-hydroxy-ketones or the silyl enol ether epoxides are formed. 

Not only oxidants with nucleophilic character but also intermediates of electrophilic nature can be used in the enantioselective epoxidation of a,p-unsaturated carbonyl compounds. Among the possible candidates, dioxirane reagents have been successfully used for this purpose. Contrary to the usual nucleophilic oxidants, dioxiranes add to double bonds in a concerted manner. These dioxiranes could be easily prepared in situ by reaction of oxone (2KHS05-KHS0 K3S0 ) with chiral ketones. Chiral ketones derived from quinic acid such as compounds 61 [67], which have been successfully used in the enantioselective epoxidation of electron rich olefins, have been also applied to the epoxidation of electron poor olefins such as chalcone 7 or a,P-unsaturated esters 59 (Scheme 4.10) to give the corresponding... 

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. 

The cyclohexyloxy(dimethyl)silyl unit in 8 serves as a hydroxy surrogate and is converted into an alcohol via the Tamao oxidation after the allylboration reaction. The allylsilane products of asymmetric allylboration reactions of the dimethylphenylsilyl reagent 7 are readily converted into optically active 2-butene-l, 4-diols via epoxidation with dimethyl dioxirane followed by acid-catalyzed Peterson elimination of the intermediate epoxysilane. Although several chiral (Z)-y-alkoxyallylboron reagents were described in Section 1.3.3.3.3.1.4., relatively few applications in double asymmetric reactions with chiral aldehydes have been reported. One notable example involves the matched double asymmetric reaction of the diisopinocampheyl [(Z)-methoxy-2-propenyl]boron reagent with a chiral x/ -dialkoxyaldehyde87. 

The ozonolysis of ethylene in the liquid phase (without a solvent) was shown to take place by the Criegee mechanism.This reaction has been used to study the structure of the intermediate 16 or 17. The compound dioxirane (21) was identified in the reaetion mixture at low temperatures and is probably in equilibrium with the biradical 17 (R = H). Dioxirane has been produced in solution but it oxidatively cleaves dialky] ethers (such as Et—O—Et) via a chain radical process, so the choice of solvent is important. 

This was also accomplished with BaRu(0)2(OH)3. The same type of conversion, with lower yields (20-30%), has been achieved with the Gif system There are several variations. One consists of pyridine-acetic acid, with H2O2 as oxidizing agent and tris(picolinato)iron(III) as catalyst. Other Gif systems use O2 as oxidizing agent and zinc as a reductant. The selectivity of the Gif systems toward alkyl carbons is CH2 > CH > CH3, which is unusual, and shows that a simple free-radical mechanism (see p. 899) is not involved. ° Another reagent that can oxidize the CH2 of an alkane is methyl(trifluoromethyl)dioxirane, but this produces CH—OH more often than C=0 (see 14-4). ... 

All classes of primary amine (including primary, secondary, and tertiary alkyl as well as aryl) are oxidized to nitro compounds in high yields with dimethyl dioxirane." Other reagents that oxidize various types of primary amines to nitro compounds are dry ozone, various peroxyacids," MeRe03/H202,"" Oxone ," ° tcrt-butyl hydroperoxide in the presence of certain molybdenum and vanadium compounds, and sodium perborate." ... 

Dimethyl dioxirane in wet acetone oxidizes isocyanates to nitro compounds (RNCO —> RN02). Oximes can be oxidized to nitro compounds with peroxytri-fluoroacetic acid, or Oxone ," sodiumperborate," among other ways. " Primary and secondary alkyl azides have been converted to nitro compounds by treatment with PhjP followed by ozone. Aromatic nitroso compounds are easily oxidized to nitro compounds by many oxidizing agents. ... 

Aryl-l,2,4,5-tetrazines are oxidised by methyl(trifluoromethyl)dioxirane to their previously unknown iV-oxides 96. NMR studies have shown that N-l is oxidised regioselectively <96X2377 >. 

Wong M-K, T-C Chan, W-Y Chan, W-K Chan, LLP Vrijmoed, DK O Toole, C-M Che (2006) Dioxiranes generated in situ from pyruvates and oxone as environmentally friendly oxidizing agents for disinfection. Environ Sci Technol 40 625-630. 

Other ketones besides acetone can be used for in situ generation of dioxi-ranes by reaction with peroxysulfate or another suitable peroxide. More electrophilic ketones give more reactive dioxiranes. 3-Methyl-3-trifluoromethyldioxirane is a more reactive analog of DMDO.99 This reagent, which is generated in situ from 1,1,1-trifluoroacetone, can oxidize less reactive compounds such as methyl cinnamate. 

In addition to metal catalyzed oxygenation of nonactivated alkane C-H bonds, oxofunctionalization of C-H bonds can also occur in water by using dioxiranes.20 Alkylketones and alkylketoesters could be regioselectively oxidized at the 5-position of the aliphatic chain by dioxiranes generated in situ by oxone in a mixture of H20/MeCN... 

Adam, W. and Hadjiarapoglou, L. Dioxiranes Oxidation Chemistry Made Easy. 164, 45-62 (1993). 

The oxidation of naphthalic acid (1,8-naphthalenedicarboxylic acid) by peroxide, rather surprisingly, does not proceed by formation of a cyclic peroxide but rather via a dioxirane [53] (a three-membered ring containing a carbon atom and a peroxide group). CL is observed from this reaction. 

The dioxirane 8a is much less labile than the carbonyl oxide 7a, and UV irradiation (A > 400 nm) is required to induce the rearrangement to lactone 9a. With 70 kcal/mol this is the most exothermic step in the whole reaction sequence from la to 9a. All of these reaction intermediates were generated in subsequent steps in high yields and characterized by matrix IR spectroscopy. 

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