Aryl-sulfur bond formation

Sulfonylation of arenes is normally performed using sulfonyl chloride and a stoichiometric amount of a Lewis or Bronstedt acid as the catalyst. Dubac and coworkers found a practical method using MW high-temperature conditions in which only 5-10 mol% FeCls (relative to the sulfonyl chloride) sufficed for complete reactions to occur [138], A number of arenes encompassing alkylbenzenes, anisole, and halobenzenes were sulfonylated by use of several different arylsulfonyl 

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A palladium-catalyzed protocol for carbon-sulfur bond formation between an aryl triflate and para-methoxybenzylthiol was introduced by Macmillan and Anderson (Scheme 6.66) [138], Using palladium(II) acetate as a palladium source and 2,2 -bis(diphenylphosphino)-l,l -binaphthyl (BINAP) as a ligand, microwave heating of the two starting materials in N,N-dimethylformamide at 150 °C for 20 min in the presence of triethylamine base led to the formation of the desired sulfide in 85% yield. 

Sulfate monoesters can react by dissociative paths, and this is the favored path. Whether such reactions are concerted or involve a very short-lived sulfur trioxide intermediate has been the subject of debate. ° Benkovic and Benkovic reported evidence suggesting that the nucleophile is present (though there is little bond formation) in the transition state for the reaction of amines with p-nitrophenyl sulfate. Alkyl esters of sulfuric or sulfonic acids normally react with C-0 cleavage only when this is disfavored, as in aryl esters, does one see S-0 cleavage. Sulfate diester... 

Reaction (7.63) shows an example of C—S bond formation [73,74]. In fact, the aryl radical formed by iodine abstraction by (TMS)3Si radical rearranged by substitution to the sulfur atom, with expulsion of the acyl radical and concomitant formation of dihydrobenzothiophene (60). This procedure... 

Recent progress on the use of hypervalent iodine reagents for the construction of heteroatom-heteroatom bonds is reviewed. Reactions of aryl-A3-iodanes with heteroatom substrates derived from third-row elements and beyond are considered first, and an unusual example of heteroatom-heteroatom bond formation with diaryliodonium salts is then discussed. Finally, the use of sulfonylimino(aryl)iodanes for imidations of phosphorus, sulfur, selenium, and arsenic compounds, including enantioselective transformations (S,Se), and alternate hypervalent iodine approaches to N-sulfonylsulfilimines and N-sulfonylarsinimines are summarized. 

The use of hypervalent iodine reagents for heteroatom-heteroatom bond forming reactions is well established in the context of classical oxidation chemistry [1-11]. For example, oxidations of anilines to azobenzenes, thiols to disulfides, and sulfides to sulfoxides with aryl-A3-iodanes were documented decades ago [1-5]. During the last ten years, particular attention has also been given to oxidative transformations of compounds derived from heavier elements, including the interception of reaction intermediates or initially formed products with external nucleophiles. A second important development is the utilization of sulfonyliminoiodanes, ArI = NS02R, for heteroatom-nitrogen bond formation, especially for imidations of sulfur, selenium, phosphorus and arsenic com-... 

Fig. 7-25. Main reactions of the phenolic /8-aryl ether structures during alkali (soda) and kraft pulping (Gierer, 1970). R = H, alkyl, or aryl group. The first step involves formation of a quinone methide intermediate (2). In alkali pulping intermediate (2) undergoes proton or formaldehyde elimination and is converted to styryl aryl ether structure (3a). During kraft pulping intermediate (2) is instead attacked by the nucleophilic hydrosulfide ions with formation of a thiirane structure (4) and simultaneous cleavage of the /3-aryl ether bond. Intermediate (5) reacts further either via a 1,4-dithiane dimer or directly to compounds of styrene type (6) and to complicated polymeric products (P). During these reactions most of the organically bound sulfur is eliminated as elemental sulfur.

The 4-(2-haloaryl)-5-aryl-l,2,4-triazole-3-thiones (316) are converted into the s-triazolo[3,4-b]benzothiazoles (317) on irradiation. SET from sulfur to the aryl ring, followed by sulfur-aryl bond formation and loss of hydrogen halide, is proposed. ... 

The oxidation of PASs with ozone leads to the formation of poly(aryl-ene sulfoxide)s with a high selectivity. This reaction takes place although ozone is an extremely strong oxidant. Thus, an appropriate amount of ozone enables either to partially or completely convert the sulfur bond into the sulfoxide bond. ° The oxidation is carried out in an ozone/inert gas stream in which the ozone is present in a concentration of 2-6% by volume. The selection of the suspension medium has a decisive influence. In methylene chloride suspension, complete oxidation to the sulfoxide is achieved in a short time. 

Smiles processes involving three-membered cyclic transition states are much less frequent under ionic conditions.However, similar Truce-Smiles processes under radical conditions are well documented. Known as neophilic rearrangements, they lead to efficient carbon-aryl bond formation with frequent extrusion of small molecules such as sulfur dioxide. These Smiles-type reactions involving cyclic transition states with a small ring size will not be evaluated further in this chapter. 

There has been a review of the use of transition-metal catalysts in the formation of C—S, C—Se, and C—Te bonds." Copper catalysis enables the formation of unsymmetrical diaryl thioethers from two differently substituted aryl iodides using ethylxanthogenate as the source of sulfur. Initial formation of an aryl xanthate, such as (17), is followed by hydrolysis to the arenethiolate, which couples with the second aryl iodide." Copper catalysis has also been used in the methylthiolation of aryl halides by DMSO. The method requires the presence of a source of fluoride ions, such as zinc fluoride." In the presence of a palladium catalyst, the reaction of aryl and heteroaryl bromides with AgSCp3 gives the corresponding trifluoromethylsulfldes." ... 

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