Sulfides sulfones using hydrogen peroxide

SELECTIVE OXIDATION OF SULFIDES TO SULFOXIDES AND SULFONES USING HYDROGEN PEROXIDE IN THE PRESENCE OF ZIRCONIUM TETRACHLORIDE... 

Furazan and furoxan sulfides and sulfones have been reported. The sulfides, formed by displacement of nitro from nitrofuroxans by thiophenols, can be oxidized to the corresponding sulfones using hydrogen peroxide. 

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. 

Various oxidants have been used in the oxidation of sulfides such as hydrogen peroxide and a number of different peroxycarboxylic acids (RC03H), the latter being the more powerful oxidising agents. In the oxidation (Scheme 18), step 1 is much faster than step 2, and consequently many sulfoxides can be prepared by this route for instance, benzyl methyl sulfoxide (26) can be obtained from benzyl methyl sulfide (25) (Scheme 19). More powerful oxidants or more vigorous conditions effect the direct conversion of sulfides into the corresponding sulfones thus, (27) and (28) are transformed into (29) and (30), respectively (Scheme 20). 

Oxidations. Glycol cleavage by NalO can be improved using the silca gel support and microwave irradiation. The oxidation of sulfides to either sulfoxides or sulfones by the same method seems to be dependent on the duration of the irradiation. Supported titanium/tartaric acid catalyst is suitable for the conversion of sulfides to sulfoxides using hydrogen peroxide as the main oxidant." ... 

The oxidation of sulfides to sulfoxides or sulfones depend on the reaction conditions used. Hydrogen peroxide and ferf-butyl hydroperoxide have both been used as also has a variety of peroxycarboxylic acids. Since all of the peroxycarboxylic acids are stronger oxidants than hydrogen peroxide, reagents such as MCPBA have been used to oxidise sulfides to sulfoxides under very mild conditions. In the example shown in Eq. (38) the diastereomeric sulfoxides were obtained in good yield [46]. 

Another method, described by Jacobsen et al. [108], involves oxidizing the sulfide in the presence of an opticEilly active Salen manganese(III) chloride complex (49). Alkyl aryl sulfides were oxidized at room temperature in 1 h with 2 mol% of catalyst using hydrogen peroxide as the stoichiometric oxidant. Sulfoxide yields are generally high (8A-95%), with minimal overoxidation to sulfone. However, enantioselectivities are only moderate 34% and 68% for 2-methoxyphenyl methyl sulfoxide and 2-bromophenyl methyl sulfoxide, respectively (Table 1.5). 

The oxidation of 2- and 5-sulfides is usually performed in acetic acid and 30% hydrogen peroxide (213, 229, 263, 345-350) Or with m-chloroperbenzoic acid (341). Ary] (8, 272. 349, 351-353) and alkyl sulfones (129, 203, 214, 270, 274, 275) are thus obtained in good yields. Other oxidative reagents such as KMn04 (7, 273) or CrO (7) in acetic add have also been used. 

A heterocyclic ring may be used in place of one of the benzene rings without loss of biologic activity. The first step in the synthesis of such an agent starts by Friedel-Crafts-like acylation rather than displacement. Thus, reaction of sulfenyl chloride, 222, with 2-aminothiazole (223) in the presence of acetic anhydride affords the sulfide, 224. The amine is then protected as the amide (225). Oxidation with hydrogen peroxide leads to the corresponding sulfone (226) hydrolysis followed by reduction of the nitro group then affords thiazosulfone (227). ... 

The oxidation of sulfides to the corresponding sulfoxides and sulfones proceeds under rather strenuous conditions requiring strong oxidants such as nitric acid, hydrogen peroxide, chromic acid, peracids, and periodate. Using MW irradiation, this oxidation is achievable under solvent-free conditions and with desired selectivity to either sulfoxides or sulfones using 10% sodium periodate on silica (Scheme 6.34)... 

Thiadiazole sulfides are readily oxidised to the corresponding sulfoxides and sulfones. For example, the sulfide (139) is converted into the sulfoxide (140) (Equation (19)) using m-chloroperbenzoic acid <84CHEC-I(6)463> and reaction of the 5-methylthio derivative (137) (R = Ph) with hydrogen peroxide in acetic acid gives the sulfone (141) (R = Ph) (Equation (20)) (89MI 408-0l>. 

The oxidation of sulfides is the most straightforward method for the synthesis of sulfoxides and sulfones.During recent years, very useful procedures involving aqueous hydrogen peroxide (H2O2) as the terminal oxidant are noteworthy due to the effective oxygen-content, low cost, safety in storage and operation and... 

Oxidation of sulfides and sulfoxides, as discussed above, and alkylation of sulfinate salts are the most common methods used to obtain sulfones for synthetic purposes [71, 109-113], A hydrogen peroxide-urea-phthalic anhydride system was recently proposed as a mild convenient reagent for the efficient preparation of sulfones from organic sulfides [114]. 

The present procedure is a specific example of the method generalized by Leonard and Johnson.8 The method employs extremely mild reaction conditions and affords high yields of sulfoxides (Note 9) free of contamination by sulfides or sulfones. Sodium periodate is easily and safely handled however, the higher cost of this reagent in comparison to certain other oxidants, e.g., hydrogen peroxide, may prohibit its use in large-scale reactions. 

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