SULFENIC COMPOUNDS

Sulfenyl chlondes react with allyl alcohols to yield allyl sulfenates, whtch are in equihbnum with the allyl sulfoxides [12] (equation 9a) These products can be oxidized to the corresponding sulfones (equation 9b) Pyrolysis of the sulfoxides gives sulfines or evidence for the presence of sulfmes Pyrolysis of sulfones leads to unsamrated compounds by extrusion of sulfur dioxide [12] (equation 9c)... 

Section 15.13 Thiols are compounds of the type RSH. They are more acidic than alcohols and are readily deprotonated by reaction with aqueous base. Thiols can be oxidized to sulfenic acids (RSOH), sulfinic acids (RSO2H), and sulfonic acids (RSO3H). The redox relationship between thiols and disulfides is important in certain biochemical processes. 

The first compound of this class with inhibitory activity on the enzyme and on acid secretion was the 2-(pyridylmethyl)sulfinylbenzimidazole, timopra-zole, and the fust pump inhibitor used clinically was omeprazole, 2-[[3,5-dimethyl-4-methoxypyridin-2-yl] methylsulfinyl]-5-methoxy- lH-benzimidazole. Omeprazole is an acid-activated prodrug. Omeprazole and the other PPIs are accumulated in the acidic space of the parietal cell due to the pKa of the pyridine nitrogen and these are converted due to protonation of the benzimidazole nitrogen first to a thiol-reactive cationic sulfenic acid and then dehydrated to form the sulfenamide (Fig. 1). These thiophilic cations then bind to luminally... 

Normally, reactive derivatives of sulfonic acids serve to transfer electrophilic sulfonyl groups259. The most frequently applied compounds of this type are sulfonyl halides, though they show an ambiguous reaction behavior (cf. Section III.B). This ambiguity is additionally enhanced by the structure of sulfonyl halides and by the reaction conditions in the course of electrophilic sulfonyl transfers. On the one hand, sulfonyl halides can displace halides by an addition-elimination mechanism on the other hand, as a consequence of the possibility of the formation of a carbanion a to the sulfonyl halide function, sulfenes can arise after halide elimination and show electrophilic as well as dipolarophilic properties. 

The sulfenic acids have been found to be extremely active radical scavengers showing rate constants of at least 107 m"1 s 1 for the reactions with peroxyl radicals at 333 K17. It has also been suggested that the main inhibiting action of dialkyl sulfoxides or related compounds in the autoxidation of hydrocarbon derives from their ability to form the transient sulfenic acids on thermal decomposition, i.e.17... 

Deprotonation of allylic aryl sulfoxides leads to allylic carbanions which react with aldehyde electrophiles at the carbon atom a and also y to sulfur . With benzaldehyde at — 10 °C y-alkylation predominates , whereas with aliphatic aldehydes at — 78 °C in the presence of HMPA a-alkylation predominates . When the a-alkylated products, which themselves are allylic sulfoxides, undergo 2,3-sigmatropic rearrangement, the rearranged compounds (i.e., allylic sulfenate esters) can be trapped with thiophiles to produce overall ( )-l,4-dihydroxyalkenes (equation 24). When a-substituted aldehydes are used as electrophiles, formation of syn-diols 27 occurs in 40-67% yields with diastereoselectivities ranging from 2-28 1 (equation 24) . ... 

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