Thioethers conversion

TS-1 (pore diameter 0.55 nm) and Ti-beta (pore diameter 0.7 nm) have been tested in the oxidation reaction of two aliphatic sulfides, ethyl sulfide (Et2S) and butyl sulfide (BU2S), in methanol (MeOH) and tert-butanol (t-BuOH) as solvents. The results obtained show that thioether conversion highly depends on the nature of the catalyst (Fig. 1). 

Although a sulfhydryl group generally is not converted to an 5-phenyl thioether, the conversion can be accomplished through the use of a Pd-catalyzed arylation with an aryl iodide. Thiophenol can be used to introduce sulfur into molecules by simple displacement or by Michael additions, and thus, the phenyl group serves as a suitable protective group that can be removed by electrolysis (—2.7 V, DMF, R N X-). ... 

Caiboo-oxygen bonds can be made using the synthetically uninteresting conversion of RMgX into ROH (shown as the firat reacdoo listed above) direct acid hydrolysis of the petxuto compound ROOMgX yields the hydroperoxide ROOM. Caibon-sulfiir bonds can be constructed using Ss to make thiols or thioethers, and similar reacdons are known for Se and Te ... 

The conversion of allylic aryl thioethers ArSCH2CH=CH2 to 6>-allylic thiophenols... 

Conversion of sulfones such as 1955 into their a-sulfonyl anions by treatment with n-BuIi at -78°C in THF then addition of bis(trimethylsilyl)peroxide (BTSP) 1949 afford, via intermediates such as 1956, aldehydes or ketones such as cyclohexanone and HMDSO 7 [146]. This reaction has subsequently been applied to the synthesis of aldehydes [147]. After hthiation with -BuLi thioethers such as phenyl benzyl sulfide 1957 react with BTSP 1949 to give mixtures of the O-silyl 1958 and C-silyl 1959 products [148]. On treatment with -BuLi at -30°C the a,a-bis-(trimethylsilyl)dimethylsulfide 1960 is, hkewise, converted into its anion, which reacts with 1949 to give the a-trimethylsilyloxy sulfide 1961 and MesSiOLi 98 [149] (Scheme 12.41). 

The hydrothiolation of terminal alkyl alkynes with 96 (Fig. 2.17) proceeds with good degree of regio- and chemo-selectivity, especially with thiophenol and p-methoxy-thiophenol as substrates. Isomerisation to the internal alkenyl thiolates accounts for less than 9% of the thiolated products under the reaction conditions. In addition, further hydrothiolation of the vinyl thioether product is not observed. Typical conversions of 70-85% at 1 mol% loading at 80°C within 5 h are observed. Arylthiols substituted with electron-withdrawing groups afford lower conversions. 

In 2000, Claver et al. reported the synthesis of novel chiral S/P ligands with a xylofuranose backbone. These thioether-phosphite ligands derived from carbohydrates were investigated for the rhodium-catalysed hydroformylation of styrene but, in spite of good conversions (>99%) combined with excellent... 

Several Pd11 complexes with thiolate or thioether derivative ligands have been studied to be applied in the hydroxycarbonylation reaction.394 Aminothiolate complexes of palladium with PPh3 catalyze the conversion of styrene to 2-phenylpropionic acid in high yield and excellent regioselectivity.644 Under mild conditions and in the presence of a catalytic amount of an S, TV-chelated palladium or//zo-amino-arenethiolate complex, styrene reacts with CO and oxalic acid or water to selectively give 2-phenylpropanic aid in high yield.645... 

The profitable conversion of thiouronium salts into dialkyl thioethers (see Section 4.1) is less successful for synthesis of diaryl thioethers. For example, l-chloro-4-nitrobenzene reacts with bis-thiouronium salts of the type (H2N)2CS(CH2) SC(NH2)2+ under soliddiquid and liquidrliquid conditions to produce the desired bis-thioethers, ArS(CH2) SAr, (20-35%), together with the diaryl sulphide, Ar2S (5-15%). Higher yields of the diaryl sulphide are observed under liquiddiquid conditions whereas, under solidiliquid conditions, the diaryl disulphide, (ArS)2, (20%) is also formed [56], Diaryl disulphides are the sole products (>65%) from the stoichiometric reaction of aryl diazonium salts with benzyltriethylammonium tetrathiomolybdate [57],... 

The conversion of S-alkyl isothiouronium salts into thioethers is aided by the addition of a phase-transfer catalyst (4.1.4.E) [30]. Similarly, a,co-dihaloalkanes are converted in a one-pot reaction into bis-sulphides (> 90%) via the isothiouronium salts (Scheme 4.3) [31]. 

Selected examples of the conversion of thiocyanates into thioethers... 

Many different pathways, mechanisms, and enzymes are associated with activation. These include dehalogenation, AT-nitrosation of secondary amines, epoxidation, conversion of phosphothionates to phosphate, metabolism of phen-oxyalkanoic acids, oxidation of thioethers, hydrolysis of esters and peroxides. The following is a summary. 

Covalent protein adducts of quinones are formed through Mchael-type addihon reachon with protein sulfhydryl groups or glutathione. Metabolic activahon of several toxins (e.g., naphthalene, pentachlorophenol, and benzene) into quinones has been shown to result in protein quinone adducts (Lin et al, 1997 Rappaport et al, 1996 Zheng et al., 1997). Conversion of substituted hydroquinones such as p-aminophenol-hydroquinone and 2-bromo-hydroquinone to their respective glutathione S-conjugates must occur to allow bioactivation into nephrotoxic metabolites (Dekant, 1993). Western blot analysis of proteins from the kidneys of rats treated with 2-bromo-hydroquinone has revealed three distinct protein adducts conjugated to quinone-thioethers (Kleiner et al, 1998). 

Interestingly, sulfonium ylides generated from electrophilic carbene complexes and sulfides can react with carbonyl compounds, imines, or acceptor-substituted alkenes to yield oxiranes [1320-1325], aziridines [1321,1326,1327] or cyclopropanes [1328,1329], respectively. In all these transformations the thioether used to form the sulfonium ylide is regenerated and so, catalytic amounts of thioether can be sufficient for complete conversion of a given carbene precursor into the... 

A combination of bromide ions and methyl octyl sulphide is able to oxidise secondary alcohols at the potential necessary to fonn bromine. Conversion of the alcohol to the ketone follows the Scheme 8.2 and uses an undivided cell with benzo-nitrile as the solvent containing 2,6-lutidine as base and tetraethylamnionium bromide. The reaction occurs using a platinum anode at 1.1 V vs-, see [28], Thio-anisole alone, in absence of bromide, will function as a catalyst for the oxidation of secondary alcohols but in these cases a more positive anode potential of 1.5 V vs. see is needed to oxidise the thioether [29]. 

In an earlier experiment, Jori et al. (14) reported that methionyl residues are important in maintaining the tertiary structure of lysozyme. The introduction of a polar center into the aliphatic side chain of methionine, as a consequence of the conversion of the thioether function to the sulfoxide, may bring about a structural change of the lysozyme molecule which, in turn, reduces the catalytic efficiency. When ozonized lysozyme was treated with 2-mercaptoethanol in an aqueous solution according to the procedure of Jori e al. (14), the enzyme did not show any increase in its activity. This may be explained in two ways. In one, such reactions are complicated by many side reactions, e.g. sulfhydryl-disulfide interchange, aggregation and precipitation of the modified enzyme (24-26). In the other, the failure to recover the activity of the enzyme may by associated with the extensive oxidation of other residues. 

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