Disulfides, diphenyl reduction

The proposed mechanism of the oxidative cleavage of S-protecting groups by the chlorosilane/sulfoxide procedure is outlined in Scheme 8. 95 The first reaction is considered to be formation of the sulfonium cation 9 from diphenyl sulfoxide (7) and the oxygenophilic silyl compound 8. The formation of a sulfonium ion of this type is known and has been utilized for the reduction of sulfoxides. 97 Subsequent electrophilic attack of 9 on the sulfur atom of the S-protected cysteine residue leads to the formation of intermediate 10, whereby the nature of the silyl chloride employed should be the main factor that influences the electrophilicity of 9. The postulated intermediate 10 may then act as the electrophile and react with another S-protected cysteine residue to generate the disulfide 11 and the inert byproduct diphenyl sulfide (12). This final step is analogous to the reaction of a sulfenyl iodide as discussed in Section 6.1.1.2.1. 

The gas-liquid chromatography with mass spectrometric detection (GLC-MS) analysis of the electrolyzed solution has shown that thiophenol is the only reduction product and the S—S bond cleavage is quantitative. Such a mechanism of bond breaking was confirmed by electrochemical studies. In cyclic voltammograms, anodic and cathodic peak potentials were the same for thiophenol and diphenyl disulfides thus the same species were participating in these processes. Electrode reactions of diphenyl disulfide are given by the following equations [166] ... 

Since the oxidative polymerization of diphenyl disulfide catalyzed by VO(acac)2 results in selective formation of thioether bonds without any oxygenated compounds such as sulfoxides and/or sulfones, it should be noted that H20 should be produced predominantly by the reduction of 02 catalyzed by the vanadium complex without the formation of partially reduced side products such as H202. 

REDUCTION, REAGENTS Bis(N-methylpi-perazinyl)aluminum hydride. Borane-Di-methyl sulfide. Borane-Tetrahydrofurane. Borane-Pyridine. n-Butyllithium-Diisobu-tylaluminum hydride. Calcium-Amines. Diisobutylaluminum hydride. 8-Hydroxy-quinolinedihydroboronite. Lithium aluminum hydride. Lithium 9-boratabicy-clo[3.3.1]nonane. Lithium n-butyldiisopro-pylaluminum hydride. Lithium tri-j c-butylborohydride. Lithium triethylborohy-dride. Monochloroalane. Nickel boride. 2-Phenylbenzothiazoline. Potassium 9-(2,3-dimethyl-2-butoxy)-9-boratabicy-clo[3.3.1]nonane. Raney nickel. Sodium bis(2-methoxyethoxy)aluminum hydride. Sodium borohydride. Sodium borohy-dride-Nickel chloride. Sodium borohy-dride-Praeseodymium chloride. So-dium(dimethylamino)borohydride. Sodium hydrogen telluride. Thexyl chloroborane-Dimethyl sulfide. Tri-n-butylphosphine-Diphenyl disulfide. Tri-n-butyltin hydride. Zinc-l,2-Dibromoethane. Zinc borohydride. 

Reduction of nitroalkenes Nitroalkenes substituted with at least one aryl group are reduced to alkenes rapidly at room temperature by reaction with NagS 9H2O and thiophenol in DMF. Thiophenol is essential as a proton source for this reduction it is converted into diphenyl disulfide during the reaction. 

The potent reductant Smh readily reduces a-alkylthio, a-sulfinyl and a-sulfonyl ketones at -78 °C A mixture of iron(II) polyphthalocyanine and thiophenol has been used to reduce a-halo, a-alkylthio, and a,a-bis(alkylthio) ketones. The iron compound apparently reacts as an electron transfer mediator the actual source of electrons is the thiophenol, which is converted to diphenyl disulfide in the course of the reaction. 

Allyl halides have been reduced with electrogenerated tris(bipyridine)cobalt(I) to afford 1,5-hexadiene [369,370]. Some of the earliest work with cobalt(I) salen involved its use for the catalytic reduction of bromoethane [371], bromobenzene [371], and /er/-butyl bromide and chloride [372]. More recently. Fry and coworkers examined the cobalt(I) salen-cata-lyzed reductions of benzal chloride [373-375] and of benzotrichloride [376], and the catalytic reductions of 1-bromobutane [377,378], 1-iodobutane [378], 1,2-dibromobutane [378], benzyl and 4-(trifluoromethyl)benzyl chlorides [379], iodoethane [380], diphenyl disulfide [381], 1,8-diiodooctane [382], and 3-chloro-2,4-pentanedione [383] have been investigated. 

Initial progress was swift and the two subunits required for the CIO-C16 dithiane fragment, sulfone 12 and aldehyde 10, were easily prepared. Ester 13 was first converted to the mono-protected diol 18 by silylation followed by ester reduction (Scheme 4). The phenyl sulfone auxiliary was next installed in two steps by a Mitsunobu-like thioether formation with diphenyl disulfide and tributylphosphine followed by oxidation with Oxone . The resulting sulfone 19 was desilylated and the liberated hydroxyl group converted to an aldehyde with Swem s procedure. Subunit 12 was completed by formation of the dithiane from aldehyde 20 under standard conditions. 

Interaction of triethyl phosphite and phenyl benzenethiosulfonate is complicated, according to Michalski et al. (223), by concurrent reduction of the sulfonate ester. Thus, in addition to ethyl benzenesulfinate and 0,0-diethyl 8-phenyl phosphorothioate (eq. 8), there is obtained diphenyl disulfide and triethyl phosphate V... 

The 14,15-double bond present in tabersonine was introduced into the /3-ethyl isomer of lactam 491 by treatment with LDA-diphenyl disulfide followed by oxidation and elimination to give the a,fl-unsaturated lactam 492. Murphy s law operated at this point, for upon lithium aluminum hydride reduction, 492 gave only a 5% yield of the amino alcohol 493. An alternative procedure was therefore developed. Hydrolysis gave a carboxylic acid, and treatment with ethyl chloroformate and triethylamine followed by sodium borohydride in aqueous THF gave a lactam alcohol 494, which after silylation was reduced with lithium aluminum hydride to amino alcohol 493 in 58% overall yield from 492. Mesylation and elimination of HC1 in refluxing chloroform gave the unsaturated mesylate salt 482. The same salt was prepared previously by Ziegler and Bennett... 

There are no electrophilic aromatic substitution reactions, analogous to those of S-dications or Se-dications, reported in the literature involving the Te-dication (58). As expected, the oxidant properties of the Te-dication are observed in reactions with 1,2-diphenylhydrazine and with benzene thiol where oxidation products, azobenzene and diphenyl disulfide, are obtained respectively. Unlike its S-dication counterpart, the Te-dication does not undergo hydrolysis with water and retains its oxidant properties. NaBH4 reduction converts the Te-dication (58) into the cyclic bis-telluride (59) <91TU537>. 

Carbonylation proceeds in the presence of chalcogen compounds without poisoning Pd catalysts. Pd-catalyzed stereo- and regioselective carbonylative double thiolation of 1-octyne with diphenyl disulfide (3) afforded the (Z)-j6-(phenylthio)--unsaturated thioester 4 [2], The thioester 4 can be converted to 3-(phenylthio)-2-alkenal 5 by Pd-catalyzed reduction with HSnBu3 under mild conditions [3]. When propargyl alcohol was subjected to the carbonylation in the presence of either diphenyl diselenide (6) or disulfide 3, 3-phenylselenobutenolide 7 or 3-phenylthiobutenolide was obtained. The transformation involves isomerization of the acylpalladium intermediate 8 to 9 [4]. 

The reduction of benzenesulfonyl chloride to diphenyl disulfide by tri-phenylphosphine (100) must be initiated by chlorine abstraction. 

A reversible uptake of the first transferring electron followed by a ratedetermining protonation step, as in the case of UQ reduction (see Eq. 10), was also reported for the reduction of oxidized glutathione [62] and of diphenyl disulfide [63] incorporated in DOPC-coated mercury, on the basis of cyclic voltammograms yielding a unit slope for the plot of FEp/(2.3 RT) versus - pH at constant v. 

The oxidative polymerization of diphenyl disulfide was carried out in the presence of a strong acid by electrolysis (198) and by reaction with Lewis acids such as SbCls (199-201) or quinones such as 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (202-205). VO catalysts such as vanadyl acetylacetonate with O2 have also been used for the oxidative polymerization (206-208), and the catalytic reaction mechanism involving four-electron reduction of O2 has been discussed (209-215). 

Both, aliphatic and aromatic disulfides such as diphenyl disulfide and di-M-butyldisulfide undergo rapid reduction to the thiol stage, each consuming 2 equiv of the hydride, 1 equiv for hydrogen evolution and 1 equiv for reduction. However, methylphenyl sulfide is inert toward Li 9-BBNH. Sulfoxides, sulfones, and sulfonic acids are inert to this reagent. 

Formamidinesulfmic acid (obtained by the oxidation of thiourea with hydrogen peroxide) has been used to reduce disulfides to sulfides (see Eqs. 12.6 and 13.22) and N-tosylsulfilimines to sulfides (see Eqs. 12.7 and 13.23), under phase transfer catalytic conditions in the presence of hexadecyltributylphosphonium bromide [15]. Diphenyl, dibenzyl and dibutyldisulfides were reduced by this method to the corresponding sulfides in 72%, 62% and 90% yields respectively. Examples of the reduction of N-tosylsulfilimines are recorded in Table 12.4. 

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