Carbon-sulfur bond cleavage reactions

Carbon-sulfur bond cleavages are extensively studied not only for synthetic applications but also for interests in catalytic desulfurization mechanism of the industrial hydrodesulfurization (HDS) process of naphtha, petroleum and lubricants 

Activation of Substrates with Polar Single Bonds 

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Photochemical, carbon-sulfur bond cleavage is also observed in compounds containing sulfur in oxidation states higher than that which exists in sulfides and in dialkyl dithioacetals. For example, the irradiation of the sulfoxide 47 in methanol produces109 a 58% yield of galacti-tol (52). Even though homolysis of the carbon-sulfur bond does occur in 47, it is unlikely that 52 results from a simple, carbon-sulfur bond-cleavage, as such a reaction predicts products that were not observed... 

Disulfides (RS-SRJ are not as useful as peroxides in their photochemical reactions, partly because carbon-sulfur bond cleavage (to give R" and RSi) competes more effectively with sulfur-sulfur bond cleavage than does C-O with 0-0 cleavage for peroxides, but largely because thiyl radicals are less reactive than their oxygen analogues. 

The reduction of sulfones with Sml2 can result in deoxygenation, to give the parent sulfide,59 or carbon-sulfur bond cleavage, depending on the substrate and the reaction conditions employed.60 For example, alkyl and alkenyl phenyl sulfones are reductively cleaved by Sml2 in the presence of HMPA. In the reduction of alkenyl sulfones, competing reduction of the electron-deficient alkene is not observed (Scheme 4.50).60... 

The photolysis of dialkylphenacylsulfonium salts and dialkyl-4-hydroxyphenyl-sulfonium salts is different from that of triphenylsulfonium salts. The latter compounds undergo irreversible photoinduced carbon-sulfur bond cleavage the former compounds, however, react by reversible photodissociation and form resonance-stabilized ylids as shown in Fig. 5. Because of the slow thermally induced reverse reaction, only small equilibrium concentrations of the ylid and acid arc present during irradiation and the concentration will rapidly decrease when photolysis has been terminated. Therefore, in contrast to triarylsulfonium salt initiation, no dark reaction will continue after the irradiation step. 

Electrolytic desulfurization of o-aminobenzyl sulfide, sulfoxide or sulfone illustrates carbon-sulfur bond cleavage. Careful control of the reaction conditions is important to achieve chemoselectivity (Scheme 17). Trifluoromethyl substituents are not reduced under the conditions used (Cd sheet ca-... 

Substituted benzenesulfonamides bearing strongly electron-attracting substituents can be reduced in slightly alkaline solution at the dropping mercury electrode to ammonia, sulfur dioxide, and a substituted benzene (Chapter 23). Saccharin is a compound of this type, and the primary electrode reaction is a cleavage of the carbon-sulfur bond chemical reactions follow the initial cleavage. 

However, unlike the triaryIsulfonium salts, these compounds undergo reversible photoinduced ylid formation rather than homolytic carbon-sulfur bond cleavage. Because the rate of the thermal back reaction is appreciable at room temperature, only those monomers that are more nucleophilic than the ylid will polymerize. Epoxides, vinyl ethers, and cyclic acetals undergo facile cationic polymerization when irradiated in the presence of dialkylphenacylsulfonium salts as photoinitiators. 

Carbon-Sulfur Bond Cleavage The Thienium Cation Diels-Alder Reaction... 

The group of Jones has described the desulfurization of thiophene and benzothiophene using [Ir2(Cp )2(H)2(p-H)] with excess TBE (t-butylethylene) or [lr(Cl)(Cp )(H)]2 in the presence of H2 [53, 106]. The reactions evenmally afford diiridium complexes with sulfide and q q -butadiene bridges and seem to proceed via two consecutive carbon-sulfur bond cleavages that require more than one metal center and the ability to form bridging thiolate intermediates (Scheme 21) [107]. 

Different alcohols and protected alcohols (as hemiacetals, silyl, methoxymethyl or phenyl ethers) were lithiated at the d-position to give the corresponding organolithium compounds. In the case of alcohols, a previous deprotonation of the hydroxyl functionality is required. The chiral intermediate 197 was prepared from the phenylsulfanyl derivative 196 first by deprotonation followed by carbon-sulfur bond cleavage with LiDTBB at low temperature. The reaction of the dianionic system 197 with y- and d-lactones in the presence of cerium(III) salts gave, after hydrolysis, spiroketal pheromones 198 (Scheme 2.27) [163]. 

Carbon—Sulfur Cleavage. The carbon—sulfur bond of DMSO is broken in a number of reactions. Attempts to form the DMSO anion by the reaction of DMSO with sodium result in cleavage accompanied by methane evolution (eqs. 10 and 11) (43) ... 

Scheme 15 shows an example of the cleavage of a carbon-sulfur bond by chlorinolysis. This reaction can also be carried out on the intact penam ring system as shown in Scheme 17 (71JA6269 and the previous paper). In Scheme 18 this reaction is used to form the epimer of... 

Other side reactions that have been reported are cleavage of the carbon-nitrogen bond to form 24 and an aminyl radical 25 or scission of the tliiocarbonyl-sulfur bond to form a thiyl radical 26 and 27 (Scheme 9.I0). U 6 4 Thiocarbonyl-sulfur bond cleavage may be a preferred pathway in the case of primary dithioearbamates. 

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