Sulfenic special

Hence, nucleophilic reactions of the superoxide ion are typical. This ion can be compared with the thiophenoxide and thiocyanate ions with respect to nucleophilicity. The cause of such high nucleophilicity lies in a so-called a-effect In 0—0 ion, an attacking site (O ) adjoins directly to a site (O ) with a significant electronegativity. This effect usually confers special activity to nucleophiles. The effect can be additionally enhanced by including the 0—0 group in sulfenate. 

The most direct approach to the four-membered S-ring is cycloaddition of sulfenes to alkenes. The sulfenes are generated in situ by base-induced de-hydrohalogenation of sulfonyl chlorides. Because of their special susceptibility to cycloaddition reactions, research into the chemistry of sulfenes is expanding. 

One of the most widely applied cycloaddition techniques for the preparation of thietanes is the reaction of sulfenes with enamines. The stereochemistry of these reactions has been extensively investigated by Truce and Rach. Whether the mechanism is a two-step or a concerted process, both in accordance with the stereoselective formation of the cis form in Scheme 1, is still unresolved. The special orientation of the 1,4-dipolar intermediate 64, in which the charged phenyl and dimethylamino moieties are in proximity, enforces the cis geometry of the resulting thietane dioxide. In the concerted mode of reaction, formation of the orthogonal oriented unsaturated system, 65 should also yield the cis cycloadduct. 

Allylic selenoxides were observed in special cases as short-lived intermediates at low temperature5. Kinetic measurements showed that the rearrangement occurs with reasonable rates4 at temperatures between — 80 °C and —20 C. The rearranged allyl selenates are easily hydrolyzed to the allyl alcohols, i.e., special reagents for cleavage, as in the case of the sulfenates, are not necessary. 

From the foregoing discussion it is evident that any discussion of the chemistry of sulfenes is in fact a description of reactions in which sulfenes are believed to be formed and then to react, without (except for the few special instances mentioned above) any direct signs of sulfene participation. The case for sulfene intermediacy is usually indirect though not necessarily lacking in rigour. In practice, we have a core of carefully studied reactions in which a number of pieces of evidence combine to prove that sulfenes are formed and then react. In addition to these, there are two classes of reactions for which sulfene intermediacy can reasonably be discussed. The first of these consists of reactions which are either straightforward extensions of known sulfene reactions for which the appropriate tests for the sulfene have not been done, or, alternatively, reactions which can be rationalized as... 

Thiol compounds can be oxidized to disulfides, or to sulfenic, sulfinic and finally to sulfonic acids. Similarly sulfides are easily converted by monpoxygenases to sulfoxides and then to sulfones. Thiocarbonyl derivatives are also substrates of monooxygenases, forming 5-monoxides (sulfines) and then 5-dioxides (sulfenes). The latter are highly reactive metabolites, specially towards nucleophilic sites in biological macromolecules, and are beUeved... 

M. Calvin Actually, simple mercaptans with iodine give a quantitative stoichiometry to make 2 RSH -H Is — RSSR 4- 2H+ -F 2 I. Now, if this R group is of a certain special type you can actually get the sulfenic iodide but in order to get that one has to have a very special kind of mercaptan. One can get it with tertiary butyl mercaptan, but not with simple mercaptans, such as cysteine or gluta-... 

Hydrogen abstraction from sulfenic acids is facilitated by production of the fairly stable sulhnyl radical. Theoretical calculations at the PM3 level performed specially for this review predict a 74 Real mol" value for the RSO-H bond dissociation energy (BDE) [18]. If this proves correct, the reaction may take place with weak hydrogen abstractors, such as peroxyl radicals, as well. 

The cycloaddition reactions are subdivided into di-, tri- and oligomerization reactions, [2-1-1]-, [2-1-2]-, [3-1-2]- and [4- -2] cycloaddition reactions and other cycloaddition reactions. The insertion reactions into single bonds are also discussed. The cyclodimerization or cyclotrimerization reactions are special examples of the [2-1-2] and the [2-I-2-I-2] cycloaddition reactions, respectively. The cumulenes vary in their tendency to undergo these reactions. The highly reactive species, such as sulfines, sulfenes, thioketenes, carbon suboxide and some ketenes, are not stable in their monomeric form. Other cumulenes have an intermediate reactivity, i.e. they can be obtained in the monomeric state at room temperature and only heat or added catalysts cause di- or trimerization reactions. In this group, with decreasing order of reactivity, are allenes, phosphorus cumulenes, isocyanates, carbodiimides and isothiocyanates. 

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