Sulphenic acids reactions

Jones and coworkers200 found that a variety of sulphenic acids may be generated by thermolysis of the readily available /J-cyanosulphoxides (equation 81) and observed their highly regiospecific addition also to non-conjugated alkynes (Table 12). As expected for a pericyclic mechanism, the reaction afforded the product of a stereospecific cis-addition. However, the regioselectivity of the addition suggests that the partial carbon-sulphur bond in the transition state 148 is polarized in such a way that the carbon atom has some cationic character (equation 82). 

For a recent discussion on the stereochemical aspects of the Diels-Alder reaction with vinyl sulphoxides see References 662, 663. It should be pointed out that vinyl sulphoxides can be considered in [2 + 4]-cycloadditions as acetylene synthons since the sulphinyl moiety may be removed from the product by sulphenic acid elimination. Paquette and coworkers took advantage of this fact in the synthesis of properly substituted anthracenes 562664, (equation 360). 

Reaction of the carbanion of chloromethyl phenyl sulphoxide 409 with carbonyl compounds yields the corresponding 0-hydroxy adducts 410 in 68-79% yield. Each of these compounds appears to be a single isomer (equation 242). Treatment of adducts 410 with dilute potassium hydroxide in methanol at room temperature gives the epoxy sulphoxides 411 (equation 243). The ease of this intramolecular displacement of chloride ion contrasts with a great difficulty in displacing chloride ion from chloromethyl phenyl sulphoxide by external nucleophiles . When chloromethyl methyl sulphoxide 412 is reacted with unsymmetrical ketones in the presence of potassium tcrt-butoxide in tert-butanol oxiranes are directly formed as a mixture of diastereoisomers (equation 244). a-Sulphinyl epoxides 413 rearrange to a-sulphinyl aldehydes 414 or ketones, which can be transformed by elimination of sulphenic acid into a, 8-unsaturated aldehydes or ketones (equation 245). The lithium salts (410a) of a-chloro-/ -hydroxyalkyl... 

Sulphoxides and selenoxides undergo syn elimination under thermal conditions. A 1,4-elimination of sulphenic acid from an allyl sulphoxide leads to dienes (equation 20)50. Precursor sulphoxides are generated by oxidation of corresponding sulphides. This reaction, however, did not give good results when applied to more complicated systems51. 

Aminopenicillanic acid (8) was converted to 6(5)-bromopenicillanic acid by trapping of the diazo-intermediate with hydrogen bromide. Esterification of the dicyclohexylamine salt (93) with p-methoxybenzyl bromide, followed by oxidation, afforded the sulphoxide (94) in 60% yield from 6-APA. Elaboration of this sulphoxide to the disulphide (96) was effected by the procedure established by Kamiya et al. [98] the sulphenic acid (95), formed by heating the sulphoxide to reflux in toluene, was intercepted by reaction with 2-mercaptobenzothiazole to yield the disulphide (96). The latter was transformed by base-catalysed double bond isomerization to the conjugated ester disulphide (97) [95% yield from (94)]. Reductive formylation of disulphide (97) then provided the formylthio-derivative (98). Cyclization of the oxalimide (99), obtained by ozonolysis of... 

Thermolytic cleavage of species like XIV form sulphenic acid, XV, Reaction (4.48) ... 

The reader will have noted that some unanswered questions were left in some of our earlier sections. For example, recall Reference 34 cited in Section V. A we did not evaluate on which side the equilibrium for reaction 54 lies. Because we subsequently considered the thermochemistry of sulphonyl sulphenates, we can now provide a partial, but admittedly long-winded, answer for the Ar = Ph species (46). The reader is reminded that A Hf(g, 46) — 52 kcal mol 1 and of the finding of Turecek and coworkers34 that the heat of formation of gaseous benzenesulphenic acid (84) is —8 kcal mol-1. Likewise, the reader may recall from Section VII.D our estimation for solid benzenesulphonic acid that AH (s, 20) = — 117 kcal mol- L These data cannot be immediately combined because of the discrepancy in the state for which the three species other than H20 are known. Do we wish to consider condensed phase species, in which case we need the sublimation energy of the sulphonyl sulphenate 46 and the sulphenic acid 84, or to consider gas phase species, in which case we need the sublimation energy of the sulphonic acid 20 ... 

We will now assume all of the species in reaction 55 are in their condensed phases and again fail to distinguish heats of vaporization and sublimation. For the sulphonyl sulphenate 46, we again use equation 47 where the ncessary value of b was derived as the sum of those for sulphones, ethers and sulphides, resulting in a predicted AHf(g, 46) value of —83 kcal mol-1. Relatedly, the value of b for sulphenic acids was taken as the sum of those for alcohols and sulphides, and thus AHf(g, 85)= —26 kcal mol-1. The left-hand side of reaction 39 is [ — 117 + ( — 26)] — [ — 83 +( — 68)] = 8 kcal mol-1 more stable than the right, where we remember that the value for PhS02—O—S—Ph is an upper bound. The results for the gaseous and condensed phases are thus seen as consonant. It is safe to say that benzenesulphonyl benzenesulfenate is best not viewed as an anhydride since its hydrolysis is endothermic. 

The sole thermochemical values known to the author for any sulphenic acid, RSOH, are the ionization and ion fragmentation reaction energetics derived values of R = Me, — 45 CH2= CH—, <4 HC=C—, 24 and Ph—, —8kcalmol-1, R. Turecek, L. Brabec, T. Vondrak, V. Hanus, J. Hajicek and Z. Havlas, Collect. Czech. Chem. Commun., 53,2140 (1988). In that we know the heat of formation of no sulphonic acid in the gas phase, we cannot provide an answer to Is it better to view the above ArS02—O—SAr species as an anhydride or an ester That is, our... 

Aromatic sulphonic acids and their salts may be produced by potassium permanganate or chromium trioxide oxidation of thiols213-216. The reaction probably occurs via the sulphenic acid route (see equation 31). Improved yields are obtained if this reaction is performed in the presence of base217 or if the reaction is performed under phase-transfer conditions218. 

Kinetic studies in the benzothiazole series include examination of the base-catalysed reaction between 2-fluoro-6-nitrobenzothiazole and aliphatic amines, " investigation of the mechanism of formation of sulphenic acid amides... 

The hydrolysis of sulphenyl halides is believed to form sulphenic acids (equation 22). These compounds, however, have never been isolated in this reaction rather thiolsulphinate esters are formed by fast reaction of sulphenic acids with sulphenyl halides (equation 23). 

Catalytic effects on the oxidation of benzenethiol by anthraquinone-1-sulphenic acid, i-butyl hydroperoxide and phenyl benzenethiolsulphinate have been observed. It was taken as evidence that sulphenate ion is a key intermediate in the reaction chain leading to the oxidized products. Indeed the above reagents may give rise to the sulphenate ion by ionization or by oxidation (equation 74) or by nucleophilic displacement (equation 75). 

Uses of Saturated Sulphides, Selenides, and Tellurldes in Synthesis.— These applications are mostly based on the C—C bond-forming reactions of sulphenyl carbanions the extensive uses of vinyl sulphides and their allyl and propargyl analogues are discussed in a later section. Some methods for C—S or C—Se bond cleavage, which are used to terminate a use in synthesis, have been discussed in an earlier section other methods, notably the conversion of the sulphide into a sulphoxide followed by pyrolytic elimination of the sulphenic acid, are covered in later sections. 

RCHjSOjSPh ) or from thiolsulphinates with NaI04 (see also preceding sections of this Chapter). Hydrolysis and other reactions that generate sulphenic acids [RS(0)C02R + HCl CICO R + RSSR + RSO SR, " and ArSBr + OH - ArSSAr, ArSR, and RSSOj", via a thiolsulphonate see also the Sulphenic Acids section] commonly lead to thiol sulphonates. Parent salts ArSOjS M+ are readily prepared. ... 

An unusual reaction of thioketen 5-oxides with azomethines leads to 1,2,4-oxathiazolidines, a representative of the still largely unknown cyclic esters of sulphenic acid (Scheme 39). The structure has been confirmed by AT-ray analysis. ... 

Apart from one citation, all the papers collected here to illustrate the reactions of vinyl sulphoxides deal with addition reactions. " As would be expected from the nature of the sulphoxide functional group, there are several novel features in these addition reactions compared with those of other vinyl compounds. Pyrolysis of alkyl styryl sulphoxides gives benzothiophens. The proposed mechanism, which involves formation and homolysis of a sulphenic acid followed by cyclization, (54) (55), is supported by the formation of benzo-... 

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