Raney nickel disulfides

Partial desulfurization of disulfides to sulfides was accomplished by treatment with tris(diethylamino)phosphine in good yields [303]. 1,2-Dithiacy-clohexane was thus quantitatively converted to thiophane (tetrahydrothio-phene) at room temperature [303]. Complete desulfurization to hydrocarbons resulted when disulfides were refiuxed in ethanol with Raney nickel or nickel boride (yields 86 and 72%, respectively) [673]. 

Two thioacetates, thiofurodysin acetate (320) and thiofurodysinin acetate (209) were isolated from a Dysidea species from Sydney, Australia. They were converted by treatment with Raney nickel to a mixture containing furodysin and furodysinin respectively [214], These were the first thiol acetates isolated from natural sources. The absolute configurations of (-)-(6/ ,ll/ )-thiofurodysinin acetate (209), (-)-(6/ ,ll/ )-furodysinin disulfide (208) and (+)-(6/ ,ll/ )-methoxythiofurodysinin acetate lactone (321), isolated from a Fijian specimen of D. herbacea were determined by chemical interconversion [292]. 

All types of electrophiles have been used with 2-lithio-l,3-dithiane derivatives, including alkyl halides, sulfonates, sulfates, allylic alcohols, arene-metal complexes, epoxides, aziridines, carbonyl compounds, imines, Michael-acceptors, carbon dioxide, acyl chlorides, esters and lactones, amides, nitriles, isocyanates, disulfides and chlorotrialkylsilanes or stannanes. The final deprotection of the dithioacetal moiety can be carried out by means of different types of reagents in order to regenerate the carbonyl group by heavy metal coordination, alkylation and oxidation184 or it can be reduced to a methylene group with Raney-nickel, sodium or LiAIII4. 

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. 

Hydrogenolysis of compounds with sulfur atoms attached to aromatic rings such as benzenethiols, and aryl sulfides, disulfides, sulfoxides and sulfones takes place on refluxing with Raney nickel or nickel boride. Sulfur combines with nickel, and hydrogen replaces the sulfur-containing group. 

Thiolate ions react with a-(alkylthio)carbonyl compounds to afford disulfides and the corresponding reduced ketone (equation 26). The reaction apparently involves direct nucleophilic attack by thiolate on the sulfur atom of the alkylthio group. Other soft bases, such as cyanide ion, thiourea and tertiary phosphines, also effect this conversion. Raney nickel of course readily desulfurizes a-alkylthiocarbonyl compounds. The reaction is quite selective for example, the ester, ketone and alkenic moieties of (43) are unaffected by the Raney nickel treatment (equation 27). Raney nickel reduction of (44) is reported to proceed with retention of configuration in ethanol and with inversion in acetone. Telluride salts also desulfurize a-alkylthio ketones. ... 

Imidazole- and benzimidazole-2-thiols usually exist largely as the thione tautomers. The thiol (thione) group is susceptible to alkylation (especially in alkaline media), and can be oxidized to sulfide, disulfide and sulfonic acid. This oxidation can often be carried out quite selectively by careful choice of oxidizing agent. The sulfur function can be removed with nitric acid, iron(III) chloride, hydrogen peroxide or, most commonly, Raney nickel. Alkyl- and arylthio groups can be oxidized to sulfoxide or sulfone. 

Thiols and thioethers, both alkyl and aryl, can be desulfurized by hydroge-nolysis with Raney nickel. The hydrogen is usually not applied externally, since Raney nickel already contains enough hydrogen for the reaction. Other sulfur compounds can be similarly desulfurized, among them disulfides (RSSR),... 

The reactivity of 120 is much less than that of either a normal alkene or a dithioacetal. Attempts to hydrogenolyze (see Section IV,3) or reduce 120 with Raney nickel, to hydrolyze the dithioacetal (see Section IV,1) with mercury(II) chloride (even in the presence of an overwhelming excess of the reagent), and to ozonize the double bond at —78°, produce only the starting material an analytical sample was prepared by extended treatment of the crude product with a concentrated, aqueous, alkaline solution of potassium permanganate at the reflux temperature.20 Acetolysis, ozonolysis, or brominolysis of 120 at room temperature affords diphenyl disulfide, and extended oxidation with hydrogen peroxide in acetone, with peroxypropionic acid, and with peroxyacetic acid, produces benzene-sulfonic acid, methyl phenyl sulfone, and an uncharacterized explosive, respectively the products occur as intractable mixtures, and the yields are invariably low. 

Hydrogenation of several 6- and 7-substituted quinoline Reissert compounds (1) in the presence of Raney nickel leads to the 2-aminomethyl-1,2,3,4-tetrahydroquinoline derivatives 68.114 A similar reduction of the Reissert compound derived from benzo[/]quinoline, followed by reaction of the crude product with carbon disulfide, gave the diazacyclopentaphenan-threne derivative 69.115... 

Sulfur-containing pyrimidines are frequent intermediates in substitution reactions. Several methods exist for exchange of the thiol group with hydrogen, either by hydrogenolysis, especially by the use of Raney Nickel, or by oxidative desulfurization which involves a sulfinic acid intermediate. Oxidation may also lead to a sulfonic acid. The 2- and 4-/6-thiones are considerably more stable to air oxidation than 5-thiol derivatives. Disulfides are conveniently formed by oxidation with bromine. Oxidation with chlorine at low temperature can be used to prepare sulfonyl chlorides. These reactions have been summarized [Pg.187]

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