Coupling, of thiols

The coupling of thiols with aryl halides has been recently reported using Ni(NHC)2 complexes [171]. After screening different pre-catalysts, compound 28 showed the best behaviour in terms of activity and substrate scope, allowing the coupling of electron rich and poor aryl bromides with aryl or alkyl thiols (Scheme 6.52). 

Several palladium catalysts for formation of aryl sulfides from aryl halides have been investigated more recently. A combination of Pd2(dba)3 and DPEphos catalyzed the formation of a broad range of diaryl sulfides in the presence of 1 mol.% palladium and NaO-t-Bu base in toluene solvent.12,rThe highest yields of alkyl aryl sulfides were obtained from aryl triflates and n-butyl thiol catalyzed by a combination of palladium acetate and BINAP. However, these reactions contained 10 mol.% catalyst, were long, and required deactivated aryl triflates. A combination of Pd2(dba)3 and DPPF catalyzed the coupling of thiols with resin-bound aryl halides.121... 

Although not directly analogous to the coupling of thiols with aryl halides, the reaction of thiourea with an aryl halide in the presence of palladium catalyst, nevertheless, can be used to generate a thiophenol from an aryl halide after hydrolysis (Equation (39)).129 This process occurred in greater than 90% yield with a variety of simple aryl halides ... 

Figure 14.11 The modification of amine-containing particles with NHS-PEG4-maleimide produces hydrophilic PEG spacers containing terminal thiol-reactive groups. Coupling of thiol-containing proteins then results in the formation of thioether linkages.

Methoxyphenylene diamine 12 was treated with potassium ethylxanthate to afford benzimidazole-thiol 13. The coupling of thiol 13 and chloromethyl-pyridine 11 was then... 

Catalysts of this type are also extraordinarily reactive for the oxidative coupling of thiols to disulfides, and the reaction is quantitative in a wide variety of organic solvents. In this case, the analogous first step would be... 

The oxidative coupling of thiols catalyzed by Fem-exchanged montmorillonite in phosphate buffer (pH 7.2) has also been demonstrated (Scheme 3.48) [151]. This system gives the corresponding disulfide as the sole product, which is in contrast to a previous report [152], where oxidation of thiols catalyzed by ion-exchanged clay gave the sulfide as the major product. 

Scheme 3.48 Oxidative coupling of thiols catalyzed by Felll-montmorillonite.

Hydrogen peroxide used over a wide pH range has been employed to oxidize sulfur compounds. The scope of the oxidation using hydrogen peroxide includes coupling of thiols to disulfides355 and thiols coupled with amines,356 which are used to produce industrially important compounds. For example, sulfenamides are accelerators for rubber vulcanization (Figure 3.91).357... 

Figure 3.91 Oxidative coupling of thiols with amines.

Saxena, A., Kumar, A., and Mozumd, S. 2007. Ni-nanoparticles An efficient green catalyst for chemo-selective oxidative coupling of thiols. Journal of Molecular Catalysis A Chemical, 269 35 0. 

Coupling of thiols. Reaction of thiols with Fe(NO,)i supported on Clayfen results in coupling to disulfides via a thionitrite, RSNO. Yields are —40-95%. 

Tetrabutylammonium chlorochromate, (C4H9)4XCr03CI, is formed by adding a solution of chromium trioxide in concentrated hydrochloric acid to a solution of tetrabutylammonium hydrogen sulfate in 5 N hydrochloric acid at 0 °C. The dry compound is used in chloroform for the oxidation of alcohols to carbonyl compounds and the oxidative coupling of thiols to disulfides [619],... 

Alkynes Alkylation of 3-alkoxy-3-(benzotriazol-l-yl)alkynes is accomplished using LHMDS as base. The products are hydrolyzed (H3O+) to furnish alkynones. Coupling of thiols with trichloroethene results in l,2-bis(alkylthio)acetylenes. ... 

In 2003, Sonogashira-type palladium-catalyzed coupling of thiol esters with... 

Co-Catalyzed Cross-Coupling of Thiols with Aryl Halides... 

An example of Co-catalyzed coupling of thiols with aryl bromides and iodides recently emerged [127]. Col2(dppe) was identified as the optimal catalyst and can be used at relatively low loadings (12). This process has excellent scope, with alkane thiols reacting in high yields. 

Like disulphide formation, the coupling of thiols and primary or secondary amines is of great industrial importance in the manufacture of rubber vulcanisation accelerators, the products being sulphenamides. 

From the numerous conjugation methods available (1), only a few are described in this chapter. One example concerns the application of the homobifxmctional cross-linker glutaraldehyde. Heterobifunctional cross-linking is illustrated by coupling of thiol-containing peptides or carriers to sulphydryl-reactive carriers or peptides, respectively. 

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