Sulphinate esters oxidation

Sulphinic acid esters have also been oxidized, to the sulphonic acid ester, with hydrogen peroxide although the reaction usually proceeds in poor yield345,346. This resistance to oxidation is also evident when other oxidants are used233,347. A much improved procedure for the oxidation of aromatic sulphinate esters uses potassium permanganate in aqueous solution, as oxidant345,348,349, as shown in equation 79. Mefa-chloroperbenzoic acid has also been used with success for the oxidative preparation of sulphonate esters. Indeed, it has resulted in the preparation of unstable sulphonate esters that are hard to form by other means350. 

Aryl sulphonyl chlorides may also be synthesized from the sulphinyl chloride, by oxidation with chlorine, in 80% yield573 (equation 146) or dimethyl sulphoxide574. Sulphinate esters may also be utilized as the precursor to sulphonyl halide via oxidative halogenation. For example, methyl methanesulphinate is converted to methanesulphonyl chloride in excellent yield at 0°C568. 

It has been proposed54 that oxidative cyclizations such as these occur via the formation of the cyclic sulphinate esters (sultines) with subsequent oxidation to the corresponding sultone as shown in equation 34 for the formation of 16. 

Sultines (cyclic sulphinate esters) can be readily oxidized to sultones by hydrogen peroxide or potassium peroxysulphate. The first example of such a synthesis was reported by King and De Mayo and their associates69 who prepared l,2-oxathiole-2,2-dioxide (22)... 

Higher temperature and the presence of alcohols would cause further oxidation of the disulphide and formation of sulphinic esters . ... 

Four-membered Rings.—Open-chain sulphinate esters are readily prepared but their cyclic analogues are less easily come by. [2 + 2]Cycloadditions involving SO2 are limited to a few specialized examples, and it has been suggested that it is this mode of reaction that leads to the initially formed adduct (274) between SO2 and ketenimines. These compounds are unstable and rearrange to thiazetidine 5-oxides (275) in 90% yield. A versatile approach has been... 

Sulphines are formed by the oxidation of thiones with peroxy-acids, but they then react further, albeit much more slowly, to give the ketone, sulphur, and sulphur dioxide. This latter reaction is kinetically similar to many other oxidations with peroxy-acids, and the results are consistent with electrophilic attack of the peroxy-acid on the C=S double bond to give a cyclic sulphinate ester (4), which rapidly decomposes to give the ketone and sulphur monoxide. In contrast, oxidation of thiobenzanilide 5-oxide with m-chloroperoxybenzoic acid gives products derived from the sulphene PhC(NHPh)=SOa. Further examples of the reaction between diarylsulphines and aryldiazomethanes to give epi-sulphoxides have been reported. ... 

Recent papers reporting on oxidation reactions of dithio-esters deal with ozonization of aromatic dithio-esters to give the corresponding sulphines, " permanganate oxidation of dithio-esters to give the corresponding thiolo-esters, and iodine oxidation of 2-phenyl-3-anilinopropenedithioates to isothiazolium tri-iodides. ... 

A full paper has been published that describes the work of Zwanenburg, Thijs, and Strating concerning the successive formation of sulphines, sulphinylsulphines, and sulphonylsulphines by the oxidation of dithio-esters with peracids. This extends the work mentioned in previous publications. Thiobenzoic acid 0-esters of part structure (282 X = an olefinic linkage, an aryl residue, or another conjugative function) have been... 

Reactions.—Asymmetric syntheses involving cr-sulphinyl carbanions have been described, including the preparation of /ff-methoxy-)ff-phenylacetaldehyde via a chiral dithioacetal mono-5-oxide anion " and of lactones, -hydroxy-lactones, and esters such as (i )-mevalonolactone. or-Sulphinyl carbanions are intermediates in the reaction of sulphines with carbanions (thiophilic addition) which can lead ultimately to ketones or olefins - (see also Chap. 3, Pt II, p. 162). 

Snlphinate Esters.—new preparation from disulphides involves chlorina-ti(m in alcohol solvents at -20 and a further new route is announced, in which N-alkyl-N -toluene-p-sulphonylhydrazines TolSOjNHNHCHi-CHjR give toluene-p-sulphinates TolSOOCHzCHzR and the alkene RCH==CH2 on oxidation with SeOz, C1O3, or HgO, probably via radical intermediates. Pyrolysis of n-butyl sulphoxylate Bu OSOBu is suggested to involve conversion into the sulphinate as first step, en route to SO2, S, Bu OH, and but-l-ene. Standard routes are illustrated in preparations of phenylmethanesulphinates and amides. ... 

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