Sulfide oxidation oxygen transfer

In Studying asymmetric oxidation of methyl p-tolyl sulfide, employing Ti(OPr-/)4 as catalyst and optically active alkyl hydroperoxides as oxidants, Adam and coworkers collected experimental evidence on the occurrence of the coordination of the sulfoxide to the metal center. Therefore, also in this case the incursion of the nucleophilic oxygen transfer as a mechanism can be invoked. The authors also used thianthrene 5-oxide as a mechanistic probe to prove the nucleophilic character of the oxidant. 

The use of dimethyldioxirane in the oxidation reactions of sulfides deserves to be mentioned [83, 84] as this mild neutral oxygen transfer reagent allows, for instance, highly reactive compounds such as a-oxosulfones to be obtained. Although the oxidation can usually be controlled at the sulfoxide level by using a stoichiometric amount of the... 

Oxometalloporphyrins were taken as models of intermediates in the catalytic cycle of cytochrome P-450 and peroxidases. The oxygen transfer from iodosyl aromatics to sulfides with metalloporphyrins Fe(III) or Mn(III) as catalysts is very clean, giving sulfoxides, The first examples of asymmetric oxidation of sulfides to sulfoxides with significant enantioselectivity were published in 1990 by Naruta et al, who used chiral twin coronet iron porphyrin 27 as the catalyst (Figure 6C.2) [79], This C2 symmetric complex efficiently catalyzed the oxidation... 

The first example of iron-catalyzed asymmetric oxidation of sulfides was described by Fontecave and coworkers in 1997 [163]. An oxo-bridged diiron complex, which contained (—)-4,5-pinenebipyridine as chiral ligand, was reported to catalyze sulfide oxidations with H202 in acetonitrile, having the potential to transfer an oxygen atom directly to the substrates. However, the enantioselectivity of this process remained rather low (<40% ee, Scheme 3.53). 

A few benzisoselenazol-3(2//)-oncs were covalently immobilized to the solid support, either silica [165] or polymer [246] (147-150) (Fig. 8). They exhibited appreciable catalytic activity similar to the activity of ebselen. The most interesting prospective oxygen-transfer catalyst is benzisoselenazolone covalently bound to a silica support (147) named HALICAT. It has been applied to hydrogen peroxide oxidation of the sulfides and TBHP oxidation of the aromatic aldehydes and alky-larenes. The catalyst can be easily filtered off from the mixture after the reaction and reused several times [165],... 

The main methodologies developed until now for enantioselective oxidation of sulfides are effective only in the oxidation of alkyl aryl sulfoxides. Dialkyl sulfoxides on the other hand are generally oxidized with only poor selectivity. In an attempt to solve this problem, Schenk s group69 recently reported a stereoselective oxidation of metal-coordinated thioethers with DMD. The prochiral thioether is first coordinated to a chiral ruthenium complex by reaction with the chloride complexes [CpRu[(S,S)-chiraphos]Cl], 36. Diastereoselective oxygen transfer from DMD produces the corresponding sulfoxides in high yield and selectivity. The chiral sulfoxides 37 are liberated from the complexes by treatment with sodium iodide. Several o.p. aryl methyl sulfoxides have been obtained by this method in moderate to high ee (Scheme 12). 

Figure 8 Examples of oxygen transfer to different substrates using hydroperoxo or alkylperoxo species A, the epoxidation of olefins catalyzed by Mo (VI) complexes as in the Oxirane process B, the Baeyer-Villiger oxidation of ketones catalyzed by Pt(II) complexes C, the epoxidation of olefins catalyzed by Ti(IV) silicates D, the oxidation of organic sulfides catalyzed by V(V) complexes.

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