Sulphenes trapping

Reactions.—Full details are now available" of the photochemical and thermal [1,3] phenylthio shifts of allyl phenyl sulphides [(73)- (74)]. Oxidation of such sulphides can lead to allyl alcohols through the known sulphoxide-sulphenate equilibrium with sulphenate trapping. 

Treatment of ethyl sulphamoyl chloride with triethylamine generates a nitrogen analogue 19 of sulphene, which has been trapped by 2-methyl-1-pyrrolidinopropene as the 1,2-thiazetidine 1,2-dioxide 20 (equation 14)33. 

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... 

Cycloaddition of diphenylisobenzofurans to (101), to sulphenes, to 2-phenyl-3-spirocyclopropylazirines, and to o-benzoquinonedi-imines have been reported. The preparation and trapping of 1-methoxy- and 1-benzyl-isobenzofuran have been described and a high degree of regio-and stereo-specificity is observed in the reactions of a range of 1-substituted isobenzofurans with quinone acetals, for example in the formation of... 

Phosphines have been used to trap sulphenes produced by dehydrochlorination of methanesulphonyl chlorides. The reaction of tetrazolo-pyridine with triphenylphosphine to give an iminophosphorane was shown, by kinetic measurements, not to involve a nitrene intermediate, but rather to involve reaction of the phosphine with the azide (12). The reaction... 

Sulphenic acids (199) have been produced transiently by thermolysis of penicillin sulphoxides and trapped both intra- and inter-molecularly. ... 

Low-valency sulphur acids continue to arouse interest. The fundamental yet elusive sulphenic acids (74) have now been generated and trapped (Scheme... 

This behaviour is illustrated in a preparation of the 2-thioxopenam (258) from the sulphoxide (259). Thus, pyrolysis of (259) induces a sulphoxide-sulphenate ester rearrangement followed by intramolecular trapping to give the disulphide (260) which is converted in two steps into the penam (258). ... 

The preparation of /3-sultones via trapping of sulphene with polyfluorinated ketones is dealt with on p. 75. 

Unsaturated Sulphoxides.—Variations of known methods for the synthesis of vinyl sulphoxides are described in reports of asymmetric selectivity in the elimination of HCl from jS-halogenoethyl aryl sulphoxides using an optically active base, leading to partially resolved vinyl sulphoxides, and in reports of the condensation of carbonyl compounds with (Et0)2P(0)CHaS(0)R in the presence of a phase-transfer catalyst. Vinyl sulphoxides are formed when sulphenic acids are trapped after generation in the presence of an acetylenic ester, and a full account is available of the trapping of the sulphenic acid of... 

Preparation.—It is possible to review syntheses of sulphenic acids and to refer now to stable products as well as fleeting species that need to be trapped in order to verify their existence. Further details of the stable penicillin-derived sulphenic acid (72) described in Volume 3 are available. The anion of (72) is, however,... 

While Cope-type elimination from -alkylidenesulphinamides gives a sulphenic acid, this undergoes further condensation reactions in the absence of a trapping agent, but, in the presence of trimethylsilyl chloride, the trimethylsilyl ester (a convenient stable source of the sulphenic acid) is formed. ... 

Reactions of Sulphenic Acids.— In addition to the trapping reactions referred to in the preceding section, the transformation products of sulphenic acids are mentioned elsewhere in this chapter. 

Thiolans, Thians, Thiepans, Thiocans, and their Oxides and Dioxides Synthesis.—The intramolecular trapping of a sulphenic acid by a carbon-carbon double bond constitutes a new stereospecific route to cw-2-substituted thiolans and thian 1-oxides. Thus 5-t-butylsulphinylpent-l-ene (1), when heated at... 

At very low temperature (-126 °C), the lithio-anion of sulphenic acid (83 t) has been trapped by alkylation (methyl fluorosulphonate) at higher temperature. 

Reactions of Sulphenic Acids.—In continuation of previous work, penicillin sulphenic acids have been trapped with vinyl ethers and keten acetals, " " with thiols, alkenes, and alkynes. A variety of products from thermolysis of N-benzyloxycarbonyl-L-(S-t-butyl)cysteinyl-L-valine methyl ester S-oxide must derive from an intermediate sulphenic acid, and isothiazolones and thiazinones formed from penicillin sulphoxides are also satisfactorily accounted for on the same basis. "... 

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