Diaryl sulfides, formation

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... 

At the time of the earlier review (66HC1155), it was already known that combinations of arenes with sulfur, or with sulfur mono- or dichlorides in the presence of Lewis acids (IV,B,1), or of aryl thiols, diaryl sulfides, or disulfides (IV,B,2 and 3) again heated with Lewis acid catalysts, generate thianthrenes, sometimes in acceptable preparative yields. A complimentary method is the treatment of aryl thiols with c. H2SO4. Routes from arenes and aryl thiols almost certainly involve the initial formation of diaryl sulfides. All these methods inevitably give symmetrical thianthrenes carrying identical substituents on each benzene ring (Scheme 9), unless the second sulfur is introduced in a controlled fashion into a preformed, unsymmetrical diphenyl sulfide. 

Deoxygenation of the diaryl sulfide (56) with triethyl phosphite gives the phenothiazine (58) in good yield via formation and rearrangement of the spiro intermediate (57). 

Treatment of activated diaryl sulfides with Na2S in DMF at 130 C results in the cleavage of the sulfide and in the formation of sodium aryl sulfides which can be used in situ to prepare mixed diaryl or alkyl aryl sulfides.183 An example is reported in Scheme 22. 

Fluorination of diaryl sulfides, selenides, and tellurides leads to the formation of diarylsulfur, selenium, and tellurium difluorides, all of... 

Scheme 39 Formation of a diaryl sulfide linkage with copper catalysis...

Oxidation of elemental sulfur and selenium with SbFs leads to the formation of doubly charged polyatomic cations [26]. These cations can react with polyfluorinated arenes to form diaryl sulfides or selenides (Eq. 12) [27]. 

By treatment with HSOsF-SbFs (1 1) and sulfur dioxide, alkylbenzenes, haloben-zenes, and alkylhalobenzenes are converted to their corresponding diaryl sulfoxides along with small amounts of diaryl sulfides as minor products (Eq. 35) [81]. In the absence of SO2 aryl sulfone formation is the dominant process, although sulfoxide is also formed. Unsymmetrical (mixed) sulfoxides can be prepared by adding one molar equivalent of an arene to the solution of the second arene and magic acid-SOa in Freon at low temperatures. 

The formation of 2-ethylthioethanol (23) involves selective nucleophilic attack by the mercapto (SH) moiety while the hydroxy group remains intact, showing that the former is a more powerful nucleophile. Thiols, as their sodio derivatives, will react with alkyl and even with aryl halides in polar aprotic solvents like DMSO and DMF to give good yields of dialkyl and diaryl sulfides (24) and (25) (Scheme 8). 

An excellent preparation of diaryl sulfides from aryl iodides and arenethiolate ions has been devised. Photolysis brings about rapid formation of the sulfide by a radical-chain process. Yields of isolated product seldom fall below 75%, Eq. (28). This ap-... 

Previously, Andersen et al. had attempted to prepare sulfuranes from the reactions of diaryl sulfoxides with aryl Grignard reagents and aryl lithium agents. They reported that the reactions give initially the corresponding triaryl sulfoni-um salts, from which two pathways, namely the formation of tetraaryl sulfuranes and the formation of benzyne, take place simultaneously, on the basis that they obtained diaryl sulfides and biaryls derived from benzyne, as shown in Scheme 7 [37]. 

The partial oxidation of sulfides to sulfoxides has been accomplished in a few cases by careful control of the reaction stoichiometry and conditions. A biphasic procedure for sulfoxide formation from diaryl sulfides is shown in eq 23. However, a more attractive and versatile procedure uses a solid Oxone-wet alumina reagent with a solution of the sulfide. This method permits control of the reaction to form either the sulfoxide or the sulfone simply by adjusting the amount of oxidant and the reaction temperature, as illustrated in eq 24. These oxidations are compatible with other functionality. 

The first successful Ar-heteroatom bond formation reaction was demonstrated in 1978 by the Japanese chemists Kosugi and Migita for a C—S bond [4]. Diaryl sulfides and arylalkyl sulfides were obtained from thiols and ArX derivatives in moderate to good yields (Scheme 3.1). 

C—S Bond Formation Dialkyl and diaryl sulfides are effective trapping reagents for aryllithium species. 

The reaction of alkyl aryl sulfides with diaryliodonium salts generated unsymmetrical diaryl sulfides in moderate to excellent yields through cleavage of the sulfur-carbon(sp ) bond and formation of a new sulfur-carbon(sp ) bond (Scheme 5.38) [60]. The synthesis was transition metal free and tolerated a host of different electron-withdrawing and donating groups. Another noteworthy aspect of the chemistry was that it was successful in an acidic environment. This renders the work complementary to the transition metal-catalyzed routes that are typically carried out under basic conditions. In related work, the... 

In 2006, Ranu reported on an t/ fz-Markovnikov hydro-thiolation of styrene derivatives 205 with disulfides using indium(I) iodide and ZnCl2. Whereas the proposed mechanism invoked the formation of indium(III) thiolate species, the regiochemical outcome of the reaction was opposite to that of In(III)-cataIyzed hydrothiolation of alkenes. It is, thus, reasonable to propose the in situ generation of sulfenyl chloride from ZnCl2 and diaryl sulfides followed by the formation of a thiiranium intermediate 207 that is reductively opened by Ini to give 208. This explanation corresponds to no reaction observed in the absence of either Ini or ZnCL. 

Reduction of 3,5,5-tris-aryl-2(5// )-furanones 115 (R, R, R = aryl) with dimethyl sulfide-borane led to the formation of the 2,5-dihydrofurans 116 in high yields. However, in the case of 3,4-diaryl-2(5//)-furanones 115 (R, R = aryl R = H or r = H R, R = aryl), the reduction led to a complicated mixture of products of which only the diarylfurans 117 could be characterized (Scheme 36) (88S68). It was concluded that the smooth conversion of the tris-aryl-2(5//)-furanones to the corresponding furan derivatives with the dimethylsulfide-borane complex in high yields could be due to the presence of bulky aryl substituents which prevent addition reaction across the double bond (88S68). 

The other fragmentation pathways are typical for diaryl sulfoxides1-4-6,1. A corresponding ortho effect was found in chlorodiphenyl ethers and sulfides but not in sulfones12 (12) were the sulfinate ester rearrangements1-4,6,11 and the consequent formation of the m/z 125 and m/z 159 ions suppress the other possible fragmentations of the molecular ions (equation 4). It is also noteworthy that the ratio [m/z 125] [m/z 159] increases with increasing distance between the chlorine and the sulfur (equation 4). 

The ring expansion reaction of diaryl cyclopropenones and cyclopropene thiones occurring with pyridinium, sulfonium, and phosphonium enolate betaine 427268-270) is related to 1,3-dipolar cycloadditions. This process results in formation of 2-pyrones 428 by loss of pyridine (or sulfide or phosphine) and insertion of the remaining fragment C=C-0 to the C1(2)/C3 bond of the cyclopropenone ... 

More decisive evidence is provided by the interconvertibility of N-aryl-JV-arylamidinothioureas (28) and Hector s bases by oxidation-reduction.63, B4,67b The former compounds are accessible (as salts) (i) by the condensation of arylthioureas (24) with arylcyanamides (23),63 (ii) by the extrusion of sulfur from the recently described40,41 s-diaryldithioformamidine hydrobromidesB4a (22), (tit) by the oxidation of arylthioureas (24) with 0.5 moles of hydrogen peroxide in the presence of mineral acids,B4a and (iv) by the mild reduction of Hector s bases by hydrogen sulfide in acid media.B4a The first of these four reactions limitB the structure of the products to the three alternatives 25, 28, and 30. Of these, 25 is excluded by the non-identity of the product with authentic67 N-phenyl-i -phenylamidinothiourea (25 R = Ph). The monosulfide structure (30) is not reconciled as readily with the observedB4a hydrolytic fission of the products into diaryl-guanidines (29) and thiocyanic acid as is structure 28. Indeed, as in the case of thioamides and nitriles (see Section II, C, 1), the present condensation may involve the primary formation of an intermediate diimido-monosulfide (30) and its isomerization to 28. 

Reaction of diarylhalo-A3-iodanes with sodium AT,AT-dialkyldithiocarbamates results in the formation of yellow or orange dialkylcarbamoyl(diaryl)-A3-iodanes, which are stable in the dark but decompose to aryl iodides and aryl dialkyldithiocarbamates in daylight via light-promoted homolytic pathway [29]. For ligand exchange of A3-iodanes with sulfides, see Section 3.2.5.4. 

The Beckmann rearrangement of ketoximes to the corresponding amides (31), the Fischer indole cyclization, isomerization of epoxides to the corresponding aldehydes, ketones, or alcohols, hydration and ammo-nolysis of epoxides, oxygen-sulfur interchange, formation of diaryl-ureas and -thioureas from condensation of aniline and carbonyl sulfide, and olefin carbonylation occur over zeolite catalysts (62). The oxo reaction over rhodium and cobalt containing zeolites recently has been claimed (22). 

The majority of syntheses of 1,4-thiazines involve the elimination of HL from species of type 11. Precursors of type 11a are not usually isolable compounds but are generated as intermediates. Two methods for the formation of such intermediates have been described one utilizes tetrahydro-1,4-thiazine-3,5-diones as starting materials, and the other requires diacyl sulfides and ammonia. Thus the synthesis of 2/f-l,4-thiazine (6), reported in 1948, was achieved by heating compound 16 at 450°C in the presence of powdered aluminum. Potentially, the procedure may be applied to the preparation of thiazines variously substituted at positions 2 and 6 however, the low yield (13%) achieved for the parent compound is a detraction. It was initially claimed that the reaction of diphenacyl sulfide with ammonia gave 3,5-diphenyl-4H-l,4-thiazine subsequent studies, however, revealed that the product was the 2//-tautomer 3,5-Diaryl-2/f-l,4-thiazines and... 

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