Peroxy acids sulfoxides

Peroxy acids usually in dichloromethane as the solvent are also reliable reagents for converting sulfides to sulfoxides... 

Section 16 16 Oxidation of sulfides yields sulfoxides then sulfones Sodium metaper lodate IS specific for the oxidation of sulfides to sulfoxides and no fur ther Hydrogen peroxide or peroxy acids can yield sulfoxides (1 mole of oxidant per mole of sulfide) or sulfone (2 moles of oxidant per mole of sulfide)... 

Peroxy acid oxidation of (17) gave sulfoxide (18) whose F NMR spectrum showed equivalent CF3 groups even at —95 °C (76JA4325). Tlie rate ratio for the sulfur walk in (18/17) is an astounding 10 ° at 25 "C theoretical reasons for the difference have been discussed (80JA286i). 

One equivalent of a peroxy acid or of hydrogen peroxide converts sulfides to sulfoxides two equivalents gives the conesponding sulfone. 

According to this correlation model, in which the principles of steric control of asymmetric induction at carbon (40) are applied, the stereoselectivity of oxidation should depend on the balance between one transition state [Scheme 1(a)] and a more hindered transition state [Scheme 1(6)] in which the groups and R at sulfur face the moderately and least hindered regions of the peroxy acid, respectively. Based on this model and on the known absolute configuration of (+)-percamphoric acid and (+)-l-phenylperpropionic acid, the correct chirality at sulfur (+)-/ and (-)-5 was predicted for alkyl aryl sulfoxides, provided asymmetric oxidation is performed in chloroform or carbon tetrachloride solution. Although the correlation model for asymmetric oxidation of sulfides to sulfoxides is oversimplified and has been questioned by Mislow (41), it may be used in a tentative way for predicting the chirality at sulfur in simple sulfoxides. 

The oxidation of sulfoxides by aliphatic peroxy acids is first order in both reactants the solvent effects have also been investigated. Thiosulfinates are oxidized by peroxy acids to thiosulfonates and not disulfoxides. It had previously been proposed that the disulfoxides are formed first but homolytically cleave and recombine to give thiosulfonates. A series of ab initio calculations were performed (at the 3-210 and 6-3IG levels) which indicate little difference in the rate of oxidation of S over S(0) in the gas phase but faster S(0) oxidation in a reaction cluster. ... 

Figure 3.95 Selective oxidation of sulfoxide over sulfide in the presence of peroxy acid anion.

The oxidation by lead(IV) acetate of iV-aminophthalimide and of several IV-aminolactams leads to the foimation of intermediates which do not undergo fragmentation or rearrangement, but which can be intercepted by alkenes, alkynes, sulfoxides and other nucleophiles. The reactions have proved particularly useful for e synthesis of aziridines from a variety of alkenes. The mechanism of these reactions has commonly been assumed to require the intermediacy of aminonitrenes, but this is probably not the case. Atkinson and Kelly have shown that oxidation of the aminolactam (25) by lead(FV) acetate at -20 C leads to the formation of an unstable IV-acetoxy compound. This is the species which can form aziridines with alkenes. The mechanism shown in Scheme 18, which is analogous to that for the epoxida-tion of alkenes by peroxy acids, has been proposed for the aziridination process. 

A variety of organic peroxy acids such as perbenzoic acid, MCPBA. monoperoxyphthalic acid, peracetic acid and trifiuoroperacetic acid are much stronger oxidants dian H2O2, and oxidize sulfides to sulfoxides under very mild conditions. Usually 1 equiv. of peroxy acid to sulfide is employed, otherwise overoxidation easily occurs to give sulfones. Among these, MCPBA has die advantage of being convenient to use and Ae oxidation is normally carried out at 0 C or lower temperatures, in di-chloromethane. The preparations of the base-sensitive sulfoxide (15), a new dienophile alkynyl sulfoxide (16), " and thiiraneradialene S-oxide (17) are typical examples. Selective oxidation of the sulfur atom of penicillins by polymer-supported peroxy acids in DMF or acetone is also known (equation 17). ... 

Many other peroxy acids, such as trifluoroperacetic acid (equation 26), peroxydodecanoic acid (equation 27) and various perbenzoic acids " are also useful oxidants to give a high yield of sulfones from sulfoxides or directly from sulfides under suitable conditions. 

Organic hydroperoxides are generally used for the preparation of sulfoxides from sulfides, - while sulfones can be obtained in neutral organic solvents in the presence of metal catalysts such as V, Mo and Ti oxides at 50-70 C. Two polymer-supported reagents which involve peroxy acid groups and bound hypervalent vanadium(V) and molybdenum(VI) compounds have been developed for facile oxidation of sulfoxides to sulfones. 

In shaip contrast to peroxy acid oxidation the oxidation of sulfoxides to sulfones with various transi tion metal salts proceeds much faster than that of sulfides to sulfoxides and consequently sulfoxides may be selectively oxidized to sulfones in the presence of sulfides. 

Since the first report in 1960, many procedures have been reported for the synthesis of optically pure sulfoxides by chemical oxidation of suMdes. Typical examples are as follows (i) the oxida-don of achiral sulfides by chiral peroxy acids,(ii) oxidation by TBHP in chiral solvents or in dra presence of chiral catalysts, and (iii) diasteieoselective oxi tion of sulfides containing another chiral center. Similar medradologies have been reported using other oxidants such as organic... 

Sulfane oxides are compounds of type R2S Om ( > 1, m = 1, 2, 3...) with the oxygen atoms present as sulfoxide or sulfone groups. For the nomenclature of organic sulfur-oxygen compounds see Table 2 for reviews on oxidized sulfur chains and rings, see Steudel. Disulfane 1-oxides, RS(0)-SR, are also known as thiosulfinates and the 1,1-dioxides are usually termed as thiosulfonates. Trisulfane 1-oxides and 1,3-dioxides, as well as tetrasulfane 1-oxides and 1,4-dioxides, have been obtained by stepwise oxidation of the corresponding sulfanes by peroxy acids (equations 151 153) 67,101,123,127,262 26s... 

Another clilTerence between sulfides and ethers is that sulfides are easily oxidized. Treatment of a sulfide with hydrogen peroxide, H2O2, at room temperature yields the corresponding sulfoxide (R2SO), and further oxidation of the sulfoxide with a peroxy acid ydelds a sulfone (R2SO2). 

The formation of A-oxides by peroxy acid oxidation of thiazoles has been reported. Reagents used and typical yields have been discussed elsewhere <1996CHEC-II(3)373>. N-Oxidation of epothilones A-C with w-chloroperbenzoic acid (MCPBA) has been reported in yields from 20% to 48%, which are typical for this type of transformation. Oxidation was confirmed to have occurred exclusively on the nitrogen atom by X-ray crystallography <1999AGE1971>, controverting an earlier report that treatment of epothilone A with MCPBA resulted in sulfoxide formation < 1997JA7960>. 

In addition to the ozonolysis of alkenes and a few aromatic compounds [93, 104], ozone oxidizes other groups. Thus saturated hydrocarbons containing tertiary hydrogen atoms are converted into tertiary alcohols [105, 106], and some alkenes are transformed into epoxides [107] or a,p-unsat-urated ketones [108], Benzene rings are oxidized to carboxylic groups [109, ethers [110] and aldehyde acetals [111] to esters aldehydes to peroxy acids [772] sulfides to sulfoxides and sulfones [775] phosphines and phosphites to phosphine oxides and phosphates, respectively [775] and organomer-cury compounds to ketones or carboxylic acids [114]. 

Peroxy propionic acid (C2H5CO3H) [340], peroxylauric acid (C11H23CO3H) [174], and other aliphatic peroxy acids [341] are used rarely, and the results do not differ appreciably from those obtained from more common peracids. The same is true of peroxypentafluorobenzoic acid, C FjCOjH, which is obtained from pentafluorobenzaldehyde and ozone and is used for epoxidations the Baeyer-Villiger reaction and the preparation of amine oxides, sulfoxides, and sulfones [342]. 

Organic peroxy acids, especially at low temperatures, oxidize sulfides to sulfoxides 163, S24], whereas tetrabutylammonium persulfate 209] at room temperature and hydrogen peroxide at higher temperatures yield sulfones 163, 324], However, hydrogen peroxide in acetic anhydride at room temperature yields sulfoxides 166], Under these conditions, double bonds resist epoxidation 163, 166, 324] (equation 553). 

The oxidation reagents used most frequently for the conversion of sulfides into sulfoxides and sulfones are hydrogen peroxide, peroxy acids, and periodates. Periodates usually do not oxidize sulfoxides to sulfones [770 771, 772, 776, 775], In addition, many other, even rather exotic, oxidants have been used especially for chemoselective oxidations of sulfides containing functional groups vulnerable to attack by peroxy compounds, such as double bonds and carbonyl groups. 

In most instances, double and triple bonds remain unaffected by the oxidation of sulfides to sulfoxides or sulfones, even when hydrogen peroxide and peroxy acids are used [163, 264, 322, 324, 506, 521], Evidently, the affinity of sulfur to oxygen is higher than that of the carbon-carbon multiple bonds (equations 574 and 575). 

A three-stage synthesis of allylic alcohols has been devised (Scheme 32)," which consists of (i) alkylation of a sulfone-stabilized allylic carbanion (ii) peroxy acid oxidation of the allylic sulfone to give a 2,3-epoxy sulfone and (iii) reductive elimination of the 2,3-epoxy sulfone to give the allylic alcohol. The overall strategy is similar to that of the Evans-Mislow allylic alcohol synthesis based on the 2,3-sig-matropic rearrangement of allylic sulfoxides. However, there are regiochemical advantages to the sul-... 

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