Alkyl sulfides, formation

Formation of Sulfides. Thiols react readily with alkenes under the same types of conditions used to manufacture thiols. In this way, dialkyl sulfides and mixed alkyl sulfides can be produced. Sulfides are a principal by-product of thiol production. Mixed sulfides can be formed by the reaction of the thiol using a suitable starting material, as shown in equations 21, 22, and 23. Vinyl sulfides can be produced by the reaction of alkynes with thiols (38). 

The preparations of aryl sulfides typically employ aryl halides as starting materials. The procedure described here makes use of the ubiquitous class of commercially available phenolic compounds in the form of aryl triflates, which expands the range of readily accessible aryl sulfides. Prior to this disclosure, the use of aryl triflates in a palladium-catalyzed process for the formation of aryl alkyl sulfides was unprecedented. This procedure appears to be general with regard to electronically neutral or electron-deficient aryl triflates (Table 1). The yields in Table I correspond to the initially disclosed procedure employing sodium (ert-butoxide as the base. Lower yields were obtained with the 4-nitro-... 

Chiral (salen)Mn(III)Cl complexes are useful catalysts for the asymmetric epoxidation of isolated bonds. Jacobsen et al. used these catalysts for the asymmetric oxidation of aryl alkyl sulfides with unbuffered 30% hydrogen peroxide in acetonitrile [74]. The catalytic activity of these complexes was high (2-3 mol %), but the maximum enantioselectivity achieved was rather modest (68% ee for methyl o-bromophenyl sulfoxide). The chiral salen ligands used for the catalysts were based on 23 (Scheme 6C.9) bearing substituents at the ortho and meta positions of the phenol moiety. Because the structures of these ligands can easily be modified, substantia] improvements may well be made by changing the steric and electronic properties of the substituents. Katsuki et al. reported that cationic chiral (salen)Mn(III) complexes 24 and 25 were excellent catalysts (1 mol %) for the oxidation of sulfides with iodosylbenzene, which achieved excellent enantioselectivity [75,76]. The best result in this catalyst system was given by complex 24 in the formation of orthonitrophenyl methyl sulfoxide that was isolated in 94% yield and 94% ee [76]. 

Corynebacterium equi IF0 3730 gave high enantioselectivity in the oxidation of aryl alkyl sulfides [106], The results listed in Scheme 6C, 11 arise from experiments with no formation of sulfone, which occurs quite easily in several cases. Thio ketals and thio acetals were oxidized into mono S-oxides by various fungal species with enantioselectivity up to 70% ee [107]. Corynebacterium equi was very successfully used in the oxidation of formaldehyde dithioacetals to mono S-oxide or sulfone-sulfoxide, depending on the substrates. Thus n-Bu-S-CH-S-n-Bu was transformed to n-Bu-S02-CH2-S(0)-n-Bu with more than 95% ee in 70% yield. 

After the first discovery of the asymmetric sulfoxidation by Kobayashi et al. [226], it could be shown that a large number of aryl alkyl sulfides are oxygenated with enantiomeric excesses higher than 98% [227-229]. Other peroxidases also catalyze this reaction. Interestingly, the plant peroxidase HRP [230] yields the (S)-sulfoxide, whereas mammalian myeloperoxidase [223] and lactoperoxidase [231] catalyze the formation of the R-enantiomers. The stereospecific sulfoxidation of aryl alkyl sulfides by purified toluene dioxygenase (TDO) from P. putida was also studied in this context [232] and showed that sulfoxidation yielded the (S)-sulfoxides in 60-70% yield, whereas CPO under the same conditions yielded 98% (R)-sulfoxides (Scheme 2.15). CPO is thus again an exception from the rule in that it produces R-enantiomeric sulfoxides, besides its bacterial origin [227]. The reason for this behavior lies in the... 

The same photolytic treatment of O-acyl esters (2) in the presence of disulfides, diselenides, and ditellurides effectively produces the corresponding alkyl sulfides, alkyl selenides, and alkyl tellurides respectively, through SHi reaction on the chalcogen atoms by alkyl radicals, as shown in eq. 8.9. The reactivities somewhat depend on the kind of chalcogenides. Thus, the effective formation of alkyl sulfides requires 30 eq. of disulfides, that of alkyl selenides requires 10 eq. of diselenides, and that of alkyl tellurides requires 2 eq. of ditellurides [27, 28]. 

Ham and coworkers85 have developed a one-pot synthetic method for the formation of aryl-alkyl sulfides, 94, from various alkyl halides and lithium aryl thiolates 93, which are prepared in situ from 92 formed by lithium—halogen exchange of 91, employing n-butyllithium (Scheme 31). The method avoids the use of unstable arylthiols and a catalyst is not required. Several aryl bromides were successfully employed in the reaction, and the corresponding sulfides were obtained in 71 to 96% yields. 

A new approach to the synthesis of annulated sulfur heterocycles based on triflic anhydride-promoted electrophilic cyclization of the hetaryl-containing alkyl sulfides, including 1409, was elaborated <2003S1191>. The proposed method includes intermediate formation of sulfonylsulfonium salts 1410 followed by electrophilic attack on the aromatic ring (Scheme 271). Smooth demethylation of initially formed cyclic sulfonium salts 1411 by treatment with EtsN afforded a number of five- 1412 and six- 1413 membered fused sulfur heterocycles. Unexpected ring opening with formation of compound 1414 took place in the reaction of diethylamine with five-membered sulfonium salt 1411. 

Benzocyclopropene reacts with a variety of radical reagents (for example A -bromosuccinimide carbon tetrachloride bromotrichloromethane bromoform/benzoyl peroxide alkyl sulfide and ethane-1,2-dithiol with photolysis) to afford products derived from cleavage of the cyclopropane ring. The preferential mode of reaction consists of a chain reaction initiated by radical addition at Cl a followed by opening of the cyclopropyl radical to afford a benzyl radical. Yields are generally low except for the addition of the alkylsulfanyl radical, e.g. formation of 1, and no products derived from addition to the central tt-bond are formed. Cyclopropa[A]naphthalene reacts similarly with radicals and gives 2-methylnapthalene derivatives, while no addition to the central 7i-bond is observed. ... 

The formation of organic sulfur compounds in salt marsh porewaters is not as well understood(H) as the inorganic moieties although progress has been made in coastal marine sediments(12). Their presence as thiols and alkyl sulfides has been determined but generally in trace amounts(12-16). The importance of these trace organic sulfur compounds to atmospheric sulfur emissions is presently an area of intense research(, 15). Less appears to be known about organic sulfur compounds in salt marsh porewaters. 

The enzymatic oxidation of various diaryl, dialkyl, and aryl alkyl sulfides by cytochrome P-450 from rabbit liver resulted predominantly in the formation of the sulfoxides with the R-configuration[16]. 

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