Electrophiles sulfides

Matsuyama, H., Minato, H., and Kobayashi, M., Electrophilic sulfides (II) as a novel catalyst. V. Structure, nucleophilicity, and steric compression of stabilized sulfur ylides as observed by 13C-NMR spectroscopy, Bull. Chem. Soc. Jpn., 50, 3393, 1977. 

C3S8, C5S7, CeSg, CeSio, and CeS. The syntheses of the sulfides involve the dithiolate complex of a transition metal ion as a precursor and are based on the oxidative coupling and electrophilic sulfiding (e.g. via S2CI2) of either the a-or anion (Figure 6) and, consequently, molecular... 

The earliest reported reference describing the synthesis of phenylene sulfide stmctures is that of Friedel and Crafts in 1888 (6). The electrophilic reactions studied were based on reactions of benzene and various sulfur sources. These electrophilic substitution reactions were characterized by low yields (50—80%) of rather poorly characterized products by the standards of 1990s. Products contained many by-products, such as thianthrene. Results of self-condensation of thiophenol, catalyzed by aluminum chloride and sulfuric acid (7), were analogous to those of Friedel and Crafts. 

Electrophilic attack on the sulfur atom of thiiranes by alkyl halides does not give thiiranium salts but rather products derived from attack of the halide ion on the intermediate cyclic salt (B-81MI50602). Treatment of a s-2,3-dimethylthiirane with methyl iodide yields cis-2-butene by two possible mechanisms (Scheme 31). A stereoselective isomerization of alkenes is accomplished by conversion to a thiirane of opposite stereochemistry followed by desulfurization by methyl iodide (75TL2709). Treatment of thiiranes with alkyl chlorides and bromides gives 2-chloro- or 2-bromo-ethyl sulfides (Scheme 32). Intramolecular alkylation of the sulfur atom of a thiirane may occur if the geometry is favorable the intermediate sulfonium ions are unstable to nucleophilic attack and rearrangement may occur (Scheme 33). 

Chloroethyldisulfides are obtained by electrophilic attack on the sulfur atom of thiiranes by sulfenyl halides (Scheme 39). Sulfur dichloride and disulfur dichloride react similarly to give more sulfur-rich derivatives di- and tri-sulfenyl halides, and tri- and tetra-sulfides (Scheme 42). A 1 1 ratio of sulfur halide to thiirane gives the di- or tri-sulfenyl halide a 2 1 ratio the tri- or tetra-sulfide. Thiirane 1-oxides are cleaved by sulfenyl halides to thiolsulfinates (Scheme 43) (74JAP7440461). 

Since sulfides tend to react with electrophiles, a method for protection could be quite useful. Sulfoxides can be used to protect sulfides and are easily formed by a variety of oxidants. Sulfides can be regenerated with thiols, SiC (0°, 15 min, TFA, anisole), LiBH4/Me3SiCl, DMF-S03/HSCH2CH2SH (DMF, Pyr, rt, 85% yield). 

The KF-S reaction presumably involves attack of a fluonnated caibanion on sulfur, whereas the S-Sbp5 reaction may involve electrophilic attack by a cationic sulfur species on the olefin under the strong Lewis acid conditions Electrophilic attack on a fluonnated olefin may also account for formation of a perfluorinated sulfide from reaction of bis(pentafluorophenyl)disulfide with hexafluoropropylene under superacid conditions [IS5] (equation 28)... 

Preparation of fluorine-containing sulfides has been achieved mainly by the reacuon of sulfenyl chlorides (RSCl), which may react with a vanety of nucleophiles The method is based on the electrophilicity of sulfur and on the leaving-group ability of chlorine... 

In the oxidative Eschenmoser sulfide contraction (Scheme 11), thioamide 59 is oxidized by benzoyl peroxide to give either a symmetrical disulfide or the O-benzoate of the thiolactam-S-oxide. In any event, the once-nucleophilic thioamide sulfur atom is now forced to adopt the role of electrophile a reactivity umpolung has, in effect, been achieved.13 The nucleophilic enamide 65 attacks the sulfur atom leading to the formation of sulfur-bridged intermediate 66. The action of a phosphine or a phosphite thiophile on the putative episulfide then gives vinylogous amidine 67. 

Several chlorophyll derivatives have been prepared by electrophilic substitution, inter alia by formylation reactions. Adopting methods from corrin chemistry.50 alkylation with chloro-methyl methyl ether (caution toxic),32k chloromethyl methyl sulfide,51 and dichloromethyl methyl ether (caution toxic)52 in the presence of Lewis acids are the methods of choice to introduce carbon residues into the chlorin frame work. The compounds listed below have been prepared by these methods. 

This, naturally, results in an increased electrophilicity of the nitrile group and also creates favourable conditions for the nucleophilic attack of the mercapto anion and an easy addition of hydrogen sulfide in accordance with the above scheme. The activation energy of the thioamidation of the model compounds is much higher (for glutarodinitrile — 11,8 [49,4] and for trinitrile - 7,97 kcal/mol [33,4 kJ/mol]) than in PAN (6,18 kcal/mol [25,9 kJ/mol]). 

Due to the fact that the nitrile groups interact with the positively charged carbon atoms of the carboxyl or ester groups more easily than the less mobile nitrile groups in the PAN macromolecules interact with each other, the electrophilicity of the nitrile groups in the macromolecules of the copolymers increases to a greater extent, which, naturally, manifests itself in the increase of the rate of hydrogen sulfide addition. 

Our recent studies on effective bromination and oxidation using benzyltrimethylammonium tribromide (BTMA Br3), stable solid, are described. Those involve electrophilic bromination of aromatic compounds such as phenols, aromatic amines, aromatic ethers, acetanilides, arenes, and thiophene, a-bromination of arenes and acetophenones, and also bromo-addition to alkenes by the use of BTMA Br3. Furthermore, oxidation of alcohols, ethers, 1,4-benzenediols, hindered phenols, primary amines, hydrazo compounds, sulfides, and thiols, haloform reaction of methylketones, N-bromination of amides, Hofmann degradation of amides, and preparation of acylureas and carbamates by the use of BTMA Br3 are also presented. 

The synthesis of a-substituted phosphonates 89, via the electrophilic addition of phosphorylated C-radicals 88 (generated by reaction of BujSnH to the readily accessible a-phosphoryl sulfides (or selenides)) and electrophilic addition to electron rich alkenes, has been described [57] (Scheme 26). A large excess of alkene is necessary to minimize the competitive formation of the undesired compound 90 resulting from direct reduction of the initial radical 88. The ratio 89/90 has been measured for each example. The synthesis of the a-mono- or a,a-di-substituted (R or phosphonates 89 shows that the free radical approach... 

One of the most readily available easily oxidized sulfides is tetrathiafulva-lene (TTF) and this material readily transfers electrons to good electrophiles such as arene diazonium salts. This reaction has been used to form the tricyclic precursor to the natural product aspidospermidine, stereospe-cifically (Scheme 1.16). Since water is very inert towards attack by free... 

They demonstrated that electron-deficient R groups and electron-rich R substituents at S accelerated the reductive elimination. They proposed 123 (Lj = DPPE, R = Ph, R = Ar) as a transition state, where R acts as an electrophile and thiolate as a nucleophile. The Hammet plot for the reductive elimination showed that the resonance effect of the substituent in R determines the inductive effect of the R group, and the effect in SR showed an acceptable linear relationship with the standard o-values. The relative rate for sulfide elimination as a function of the hybrid valence configuration of the carbon center bonded to palladium followed the trend sp > sp spl... 

Other kinds of nucleophiles such as amines, alkoxides, and sulfide anions also react with electrophilic alkenes, but we focus on the carbon-carbon bond forming reactions. 

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