Sulfoxides diaryl, oxidation

Kinetic studies of the oxidation of diaryl sulfoxides by Crvi led to the proposition of a single electron transfer67 as in the case of aryl methyl sulfoxides68. These reactions were performed in aqueous acetic acid/perchloric acid medium, HCr03+ being the active... 

Mislow and co-workers (258) and Hammond (259) have shown that optically active diaryl sulfoxides, which are configurationally stable in the dark at 200°C, lose their optical activity after 1 hr at room temperature on irradiation with ultraviolet light. Similarly, an easy conversion of the trans isomer of thianthrene-5,10-oxide 206a into the thermodynamically more stable cis isomer takes place upon irradiation in dioxane for 2 hr. However, the behavior of a-naphthylethyl p-tolyl sulfoxide under comparable irradiation conditions is different, namely, it is completely decomposed after 4 min. These differences are not surprising because the photochemical racemization of diaryl sulfoxides occurs by way of the pyramidal inversion mechanism whereas decomposition of the latter sulfoxide occurs via a radical mechanism with the cleavage of the sulfur-carbon bond. It is interesting to note that photoracemization may be a zero-order process in which the rate depends only on the intensity of the radiation and on the quantum yield. 

Various diaUsyl, alkyl aryl and diaryl sulfoxides were readily oxidized to the corresponding sulfone in excellent yields under mild conditions at —30°C by 51. Interestingly,... 

The benzothiadiazepine 1-oxides (550), formed by the reaction of the diaryl sulfoxides (549) with hydrazoic acid, rearrange on treatment with sodium hydroxide to give (551) (72CB757). The benzothiadiazine 1,1-dioxide (552) also undergoes base-induced ring expansion to give (553) (71JOC2968). 

Furukawa, N. Ogawa, S. Matsumura, K. Fuji-hara, H. Extremely facile ligand-exchange and disproportionation reactions of diaryl sulfoxides, selenoxides, and triarylphosphine oxides with organolithium and Grignard reagents. 

Equation 20) - only two examples (X=F, (CF3)2NO) (2) reaction of arylchloromethyl tolyl sulfoxides with S4N4 (Equation 25) - only 3,5-diaryl 1-oxide products, moderate yields, and many by-products (3) displacement of the chloro atoms of l,3,5-trichloro-lX, -l,2,4,6-thiatriazine (Equation (13) Schemes 22 and 25-28). Method (3) is the best and most general recent method, though (to date) restricted to heteroatom-linked substituents at C-3 and C-5. 

Oxidation of Sulfoxides. Dialkyl, alkyl aryl, and diaryl sulfoxides are readily oxidized to sulfones in excellent yields under mild conditions (—30 °C) in MeCN by the peroxy intermediate (1). Oxidation of the unsaturated sulfoxide (11) was chemose-lective it furnished the sulfone (12) in 70% yield when reacted with (1) for 5 h. The double bond was not epoxidized. Similar chemoselective epoxidation has been carried out with only one other reagent (potassium hydrogen persulfate). ... 

Miscellaneous Reactions. Bromodimethylborane can also be used to convert dialkyl, aryl alkyl, and diaryl sulfoxides to the corresponding sulfides (eq 15). Typically, the sulfoxides are treated with 2.5 equiv of Me2BBr in dichloromethane at —23 °C for 30 min and at 0°C for 10 min. Bromine is produced in the reaction and must be removed in order to avoid possible side reactions. This is accomplished by saturating the solution with propene prior to introducing the reagent or by adding cyclohexene. Phosphine oxides and sulfones failed to react under the conditions used to deoxygenate sulfoxides. 

Sulfonyloxaziridines were recently proposed as O-transferring reagents. Oxaziridine (89) converted thioethers to sulfoxides (90) and diaryl disulfides into their 5-oxides (91) (78TL5171). Epoxidations are also possible (81TL917). 

Oae and coworkers oxidized several diaryl, dialkyl and alkyl aryl sulfides to their corresponding sulfoxides using purified cytochrome P-450 obtained from rabbit liver microsomes138. In agreement with expectations, this enzyme did not exhibit much stereospecificity. Some examples including the observed e.e. values are shown by 121-125. A model was proposed to account for the absolute configurations of the sulfoxides produced (126). The sulfur atom is preferentially oxidized from the direction indicated. 

With this encouraging result from the model system, a gram quantity of the racemic sulfoxide 40 was prepared by oxidation of benzoxathiin 16 with mCPBA and a small amount of chiral sulfoxide (A)-40 with 94% ee was isolated by subsequent chiral HPLC separation (Scheme 5.12). When chiral sulfoxide (S)-40 was treated with borane-dimethylsulfide, a clean reduction of the olefin and the sulfoxide was observed. More surprisingly, only the desired cis-diaryl dihydrobenzoxathiin 12 was observed in high yield and unchanged 94% ee. No trans-isomer or 16 was observed. With this proof of concept in hand, an efficient... 

Reactions of arylchloromethyl-p-tolyl sulfoxides with tetrasulfur tetranitride (S4N4) yield 3,5-diaryl-1,2,4,6-thiatriazine 1-oxides <00T7153>. [4+2] Cycloadditions of thiazyl... 

It has been shown that a phase-transfer catalyst could control the oxidation of sulfide to the corresponding sulfoxide. Thus, the oxidation of diaryl sulfides to sulfoxides using Oxone and PTC (equation 54) is in contrast with the reaction in polar solvents without PTC which gives sulfones as a major product. 

Various alkyl aryl and diaryl sulfides were oxidized selectively to the corresponding sulfoxides in high yields as the major products using sulfonylperoxy intermediate 51 (equation 86) ". ... 

This I04 -5i02 reagent is not very elective in the oxidation of sulfides into sulfoxides. However, sulfuryl chloride adsorbed wet silica gel is an excellent reagent for this transformatim (equation 5). High yields of methyl aryl, diaryl, allylic. benzylic and dialkyl sulfoxides are thus obtainable. The procedure commends itself by its simplicity and its extension to thioacetals provides a good, quantitative re-... 

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