Nucleophilic Attack on Sulfur

Reactivity of Five-membered Rings with One Heteroatom 

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Reactions of the Disulfide Group. Besides the thiol end groups, the disulfide bonds also have a marked influence on both the chemical and physical properties of the polysulftde polymers. One of the key reactions of disulfides is nucleophilic attack on sulfur (eq. 4). The order of reactivity for various thiophiles has been reported as (C2H O) P > R, HS , C2H5 S- >C,H,S- >C,H,P,... 

Oxygen nucleophiles usually attack a ring carbon atom rather than the sulfur atom of a thiirane, and those cases in which desulfurization is observed on treatment of a thiirane with oxygen bases probably involve the extrusion of sulfur by mechanisms other than a nucleophilic attack on sulfur, e.g. thermal. Desulfurization of thiirane intermediate (43)... 

As shown, an asymmetric carboxylic-sulfonic acid anhydride is formed, but the cellulose attack occurs on the C = O group, since a nucleophilic attack on sulfur is slow, and the tosylate moiety is a much better leaving group than the carboxylate group [193]. Similar to other acylation reactions, there is a large preference for tosylation at the 5 position, and cellulose tosylates... 

In a preliminary step, adjacent ester groups undergo initial hydrolysis or alcoholysis, by the base, to the oxide anion. This step is reasonable for carboxylic esters, which are rapidly hydrolyzed under the conditions usually employed, but is rather more surprising for sulfonic esters, which are usually hydrolyzed only slowly by the nucleophilic attack on sulfur required for this reaction. With these disulfonic esters, the ease of hydrolysis has been explained by the inductive effect of the adjacent sulfonyloxy group.7... 

The ring-opening reactions of nitrothiophenes and nitrobenzo[/ ]thiophenes are discussed in Section 3.10.4.2.1. Another interesting ring opening is initiated by a nucleophilic attack on sulfur this is discussed in Section 3.10.2.5.4. 

While most nucleophiles react with the fused thiiranium salt at carbon (Section 1.06.6.5), certain soft nucleophiles including anion of malonate ester, iodide, thiourea, phosphines, and tertiary amines promote elimination of the sulfur atom by nucleophilic attack on sulfur (Scheme 36) <1980T1361>. 

The 2-phenacylisothiazolium bromides 79b-d, synthesized by reaction of the corresponding isothiazole with phenacyl bromide (see Scheme 24), were treated with pyridine and afforded 2-benzoyl-2i/-l,3-thiazines 394b-d via deprotonation of the exocyclic methylene group to 393 followed by intramolecular nucleophilic attack on sulfur atom (85BSB149, Scheme 132). 

In the case of RFS02Br and RFS02I, no product resulting from nucleophilic attack on sulfur has been observed, and reactions with various nucleophiles invariably involved a... 

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