Sulfides oxidation to sulfones

The H0F-CH3CN complex readily oxidizes sulfides to sulfones.120 The electrophilic nature was confirmed by an X o value (see Peroxides and Peracids for a discussion of Xgo) of 0.45. Examples include electron-deficient sulfides that cannot be oxidized to sulfone by any other method. 

Oxidation of sulfides. The mixture of reagents (TPAP as catalyst, NMO as co-oxidant) oxidizes sulfides to sulfones in MeCN in the presence of 4A-molecular sieves. Isolated double bonds are generally not affected. 

NaI04 in an absolute alcohol can be used as oxidant, since neither reagent oxidizes sulfides to sulfones. 

Sulfur Compounds. Some of the earliest applications of Oxone in organic synthesis involved the facile oxidation of sulfur functions. For exanqile, aqueous Oxone selectively oxidizes sulfides to sulfones even in highly functionalized molecules, as... 

Sulfur Compounds. Some of the earliest applications of Oxone in organic synthesis involved the facile oxidation of sulfur functions. For example, aqueous Oxone selectively oxidizes sulfides to sulfones even in highly functionalized molecules, as illustrated in eq 22. Sulfones can also be prepared by a convenient two-phase system consisting of a mixture of solid Oxone, wet montmorillonite KIO clay, and a solution of the sulfide in an inert solvent. ... 

Polyoxometalates WZnMn2(ZnW9034)2 were employed to oxidize sulfides to sulfones in moderate selectivity (85-90% selectivity with 10-15% of sulfone) [23]. 

When the desired product is a sulfoxide sodium metaperiodate (NaI04) is an ideal reagent It oxidizes sulfides to sulfoxides m high yield but shows no tendency to oxidize sulfoxides to sulfones... 

The conversion of cyclic sulfides to sulfones is accompbshed by more energetic oxidations. Perhalogenated thiolanes [106] and 1,3-dithietanes [107] are oxidized to sulfones and disulfones, respectively, by a mixture of chromium trioxide and nitric acid (equation 98) The same reagent converts 2,4-dichloro-2,4-bis(tnfluoromethyl)-l,3-dif/u cto cs to disulfone derivatives [107], whereas trifluoromethaneperoxysulfonic acid converts the starting compound to a sul-fone-sulfoxide derivative [2(equation 99). 

The enzymatic oxygenation process is of particular value as there is a significant difference in the formation rates of sulfoxides and sulfones. The initial conversion of sulfide to the optically active sulfoxide by an MO is usually very fast compared to the subsequent oxidation step to sulfone, upon which chirality is lost (Scheme 9.26). In many cases, over-oxidation to sulfone is not observed at all when employing MOs. 

Sulfones. This oxidant is useful for selective oxidation of sulfides to sulfones (10,328). Oxidations of acid-sensitive substrates should be buffered with Na2C03. 

Scheme 8 summarizes the introduction of the missing carbon atoms and the diastereoselective epoxidation of the C /C double bond using a Sharpless asymmetric epoxidation (SAE) of the allylic alcohol 64. The primary alcohol 62 was converted into the aldehyde 63 which served as the starting material for a Horner-Wadsworth-Emmons (HWE) reaction to afford an E-configured tri-substituted double bond. The next steps introduced the sulfone moiety via a Mukaiyama redox condensation and a subsequent sulfide to sulfone oxidation. The sequence toward the allylic alcohol 64 was com-... 

Oxidations of sulfides catalysed by Ru porphyrin complexes have been reviewed [4, 97, 98]. In their pioneering work of 1953 Djerassi and Engle showed that stoich. RuOyCCl oxidised several sulfides to sulfones (Table 5.2) [99]. 

Oxidation of sulfides and sulfoxides using Oxone dispersed on silica gel or alumina was reported . A study of surface mediated reactivity of Oxone compared its reactivity with that of ferf-butyl hydroperoxide. Oxidation of sulfides to sulfones in aprotic solvents mediated by Oxone on wet montmorillonite or clay minerals proceeds in high yields. Interestingly, when Oxone on alumina is applied for selective oxidation of sulfides in aprotic solvents, the product distribution is temperature-dependent and sulfoxides or sulfones are obtained in good to excellent yields (equation 56) . ... 

Oxidation of a snlfide to sulfoxide is known to be an electrophilic reaction, in contrast with nncleophUic oxidation of sulfoxide to sulfone. Since 2-nitrobenzenesulfinyl chloride/KOi oxidizes sulfides to sulfoxides selectively, intermediate 48 must be the actual active intermediate. Moreover, in the presence of l,4-diazabicyclo[2.2.2.]octane (DABCO), which is a radical capturing reagent, the oxidation of methyl phenyl sulfide to the sulfoxide was inhibited. In order to further detect the intermediate 48, pure 5,5-dimethyl-l-pyrroUne-l-oxide (DMPO) was used as a trapping reagent and spin adduct was obtained. The ESR spectrum of the DMPO spin adduct was obtained by the reaction of 02 with 2-nitrobenzenesulfinyl chloride (hyperfine coupling constants, aH = 10.0 G and aN = 12.8 G). 

THE FIRST EXAMPLE OF DIRECT OXIDATION OF SULFIDES TO SULFONES BY AN OSMATE-MOLECULAR OXYGEN SYSTEM... 

The oxidation of sulfides to sulfones has been the subject of extensive studies, since sulfones are useful synthons for the construction of various chemically and biologically significant moleculesJ Recently, a new catalytic system has been developed by exchanging potassium osmate onto chloride-saturated layered double hydroxides (Figure 9.1), which we have shown to be an efficient catalyst for the direct oxidation of sulfides to sulfones, using molecular oxygen as the stoichiometric oxidant and with delivery of two oxygen atoms simultaneously to the sulfide, reminiscent of olefin dihydroxylation reactions. 

Sulfunes. A recent preparation of thietane 1,1-dioxide1 emphasizes the advantage of tungstic acid catalysis2 in the hydrogen peroxide oxidation of sulfides to sulfones an induction period is eliminated and the yield improved. 

Oxidation of sulfides to sulfones.[ Sulfides are oxidized chemoselectively to sulfones by KHSOs (3 equivalents) in high yield. Peracids are usually used for this oxidation, but can also oxidize olefinic groups. Oxidation of sulfides to sulfoxides is also possible with 1 equivalent of reagent. 

A recent method for the highly chemoselective oxidation of sulfides to sulfones using Af-methylmorpholine IV-oxide (NMP) and a catalytic perruthenatc was found to be also applicable in the presence of isolated or allylic double bonds [115]. 

Gokel, G.W., Gerdes, H.M., and Dishong, D.M., Sulfur heterocycles. 3. Heterogenous, phase-transfer, and acid catalyzed potassium permanganate oxidation of sulfides to sulfones and a survey of their carbon-13 nuclear magnetic resonance spectra, J. Org. Chem., 45, 3634, 1980. 

RlSR2 —> R S(0)R2. This sulfinyl chloride is oxidized by potassium superoxide to a sulfinyl peroxy intermediate that oxidizes sulfides to sulfoxides at —25° in >90% yield with only traces of the corresponding sulfones.1... 

Inorganic peroxygens have also been used to oxidize sulfur centres, particularly sodium perborate, which is excellent for oxidizing electron-deficient sulfides to sulfones.412 Sodium perborate tetrahydrate has been used to stereo-specifically oxidize a-methylbenzylamine thiols in acetic acid.413 The use of organic peracids such as MCPBA was not found to be stereospecific for the above mentioned oxidation. 

Sodium percarbonate (PCS) can also be employed for the oxidation of sulfides to sulfones in acetonitrile assisted by ultrasound.415... 

Bipyridinium chlorochromate (4) is a mild, air stable nonhygroscopic oxidant. It is weaker than PCC, and thus 2-4 equiv. are required to obtain good yields of carbonyl compounds. The bipyridyl system acts as an internal buffer, permitting the ready oxitktion of alcohols in sul trates with acid labile groups. Bipyridinium chlorochromate will also oxidize sulfides to sulfoxides and sulfones." ... 

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). ... 

A number of other oxidants which produce sulfones from sulfoxides are known, such as N02BF4, ° oxygen with Ir or Rh catalysts, ozone,KHSOs (Oxone) and K2S20s. Oxone is a highly chemoselective oxidant for the conversion of sulfides to sulfones without affecting hydroxy or al-kenic groups (equation 37). Similarly flavin (14) oxidizes aryl methyl sulfoxides to sulfones fairly selectively. ... 

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