Dioxiranes

Dioxiranes have been successfully used for the selective oxidation of sulfides to sulfoxides (Eq. (8.1)) [11]. 

These reactions are rapid, and the sulfide is efficiently oxidized to sulfoxide as the only product vith no overoxidation to sulfone. The reaction is thought to proceed via direct oxygen transfer from the oxirane to the sulfide. In a mechanistic study [12], it was found that a hypervalent sulfurane is an intermediate in the reaction, being in equilibrium with the electrophilic zwitterionic intermediate formed from electrophilic attack by the peroxide on the sulfide. 

The oxirane oxidation of sulfides has found applications in organic synthesis [13, 14]. For example, sulfoxidation of disulfide 1 with dioxirane afforded disulfoxide 2 in 98% yield (Eq. (8.2)) [13]. 

The corresponding sulfoxidation of 1 with MCPBA was unsuccessful and gave only 9% of disulfoxide 2 together with substantial amounts of degraded dicarbonyl compound (29%) and monosulfoxide 3 (49%). Other applications of sulfoxidation with the use of dioxirane are given in Ref. [14]. 

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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. 

Dioxiranes are three-membered cychc ring peroxides that ate expected to... 

Two unstable and explosive dioxiranes, hexaduorodimethyldioxirane [35357-46-1] and chloropentaduorodimethyldioxirane [35357-48-3] have been synthesized (105). 

In the late 1970s, evidence showed that diaLkyl dioxiranes were generated in ketone—caroate, 2KHSO KHSO K SO, systems (106) and the mechanism of the reaction was determined (88,90) ... 

There is evidence that dioxirane is an intermediate product in the low temperature ozonization of ethylene and is probably formed from the diradical resonance isomer of the 1,3-zwitterion (164). 

The peroxidic three-membered dioxirane (16) (80JOC4758) and the thiaziridinimine (17) (76JOC3403) were made plausible as intermediates, but there was no direct proof of their existence. 

Development of chiral, nonracemic dioxiranes for the catalytic enantioselective epoxidation of alkenes 99SL847. 

Enantioselective epoxidation of unfunctionalized alkenes was until recently limited to certain ds-alkenes, but most types of alkenes can now be successfully epoxi-dized with sugar-derived dioxiranes (see Section 9.1.1.1) [2]. Selective monoepox-idation of dienes has thus become a fast route to vinylepoxides. Functionalized dienes, such as dienones, can be epoxidized with excellent enantioselectivities (see Section 9.1.2). 

Asymmetric epoxidation of terminal olefins has remained problematic, despite the general success of the novel dioxirane-based catalysts. The enantiomeric excesses in these reactions do not usually exceed 85% (see Section 9.1.1.1). As recrystallization of epoxides can be complicated, enantiopure terminal epoxides are difficult to obtain. 

Raushel, F. M., and Baldwin, T. O. (1989). Proposed mechanism for the bacterial bioluminescence reaction involving dioxirane intermediate. Biochem. Biophys. Res. Commun. 164 1137-1142. 

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. 

Many other reagents for converting alkenes to epoxides,including H2O2 and Oxone , VO(0-isopropyl)3 in liquid C02, ° polymer-supported cobalt (II) acetate and 02, ° and dimethyl dioxirane.This reagent is rather versatile, and converts methylene oxiranes to spiro-epoxides. ° ° One problem with dimethyloxirane is C—H insertion reactions rather than epoxidation. Magnesium monoperoxyphthalate is commercially available, and has been shown to be a good substitute for m-chloroperoxybenzoic acid in a number of reactions. 

Cyclic 1,2-diamines are cleaved to diketones with dimethyl dioxirane. a-Diketones and a-hydroxy ketones are also cleaved by alkaline H202. HIO4 has... 

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. ... 

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