Thiols Raney nickel

Thiol groups in the 2-, 3- and 6-positions have been desulfurized with Raney nickel under the usual conditions to give the corresponding unsubstituted compounds. 

The hydrogenolysis of the thiol esters of carboxylic acids offers a delicate method for reducing an acid to the corresponding aldehyde or alcohol application of this method to the sugar series has been made by Wolfrom and Karabinos who reduced D-ribonyl chloride tetraacetate (LXXV) to aldehydo-D-ribose tetraacetate (LXXVII) in 22% yield via ethyl thiol-D-ribonate tetraacetate (LXXVI). The desulfurization of the thiol ester (LXXVI) was carried out with a somewhat aged sample of Raney nickel" which doubtless had less activity than the... 

Desulfurization by refluxing with Raney nickel in 70% ethanol for 6 hours converted thiol esters to aldehydes in 57-73% yields (exceptionally 22% yield) [1101] ( Procedure 6, p. 205). Desulfurization of a dithioester, methyl dithio-phenylacetate, by refluxing with Raney nickel in 80% ethanol for 1 hour afforded 65% yield of ethylbenzene [1102]. 

DESULFURIZATION WITH RANEY NICKEL Preparation of Aldehydes from Thiol Esters [1101]... 

The compound in which the 3-keto group is reduced to a hydrocarbon interestingly still acts as an orally active progestin. The preparation of this compound starts with the hydrolysis of dihydrobenzene (13-2) to afford 19-nortestosterone (15-1). Reaction with ethane-1,2-thiol in the presence of catalytic acid leads to the cyclic thioacetal (15-2). Treatment of this intermediate with Raney nickel in the presence of alcohol leads to the reduced desulfurized derivative (15-3). The alcohol at 17 is then oxidized by any of several methods, such as chromic acid in acetone (Jones reagent), and the resulting ketone (15-4) treated with hthium acetylide. There is thus obtained the progestin lynestrol (15-5) [18]. 

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]. 

Thiols and thioethers,413 both alkyl and aryl, can be desulfurized by hydrogenolysis with Raney nickel.414 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 ... 

Reactions of 4,7-phenanthroline-5,6-dione have been the subject of considerable study. It is reduced to 5,6-dihydroxy-4,7-phenanthroline by Raney nickel hydrogenation226,249 or by aromatic thiols in benzene,262 and oxidized by permanganate to 3,3 -bipyridyl-2,2 -dicarboxylic acid.263 It forms bishemiketals with alcohols226 and diepoxides with diazomethane.226 The diepoxides by reaction with hydrochloric acid form diols of type 57, R = Cl, which on oxidation with lead tetraacetate give 3,3 -bipyridyl diketones of type 58, R = Cl. Methyl ketones of type 58, R = H, are also obtained by lead(IV) acetate oxidation of the diol 57, R = H, obtained by lithium aluminum hydride reduction of 57, R = Cl. With phenyldiazomethane and diphenyldiazomethane the dione forms 1,3-dioxole derivatives,264,265 which readily hydrolyze back to the dione with concomitant formation of benzaldehyde and benzophenone, respectively. 

The thiocyanurates are readily hydrolyzed in acid to cyanuric acid and a thiol. Trimethyl trithiocyanurate reacts with sodium sulfide to give the trisodium salts. Melamine is formed on treatment of the thiocyanurates with aqueous ammonia at high temperatures the alkylthio groups are replaced sequentially <59HC(l3)l,p.lll), and can be removed using Raney nickel (equation 25) . 

Thioketals, unlike ordinary ketals, are formed readily from ketones and thiols (RSH) in the presence of acid catalysts. The desulfurization procedure usually goes well, but the product is rather difficult to separate by extraction from the large excess of Raney nickel required for optimum yields. 

Crystalline aldehydo-D-ribose tetraacetate (XXXII) has been prepared through the Rosenmund reduction of tetraacetyl-D-ribonyl chloride (XXXI),101 through the selective hydrolysis of tetraacetyl-D-ribose diethyl thioacetal (XXX)109 and through the Raney nickel hydrogenolysis of ethyl thiol-D-ribonate tetraacetate (XXXIII).103-104 The substance has been used in the synthesis of 2,3,4,5-tetraacetyl-D-ribitoll0B and in the synthesis of ribitylaminobenzenes.108... 

Desulfurization (13, 158-159).1 In addition to desulfurization of thiols, thioethers, sulfoxides, and sulfones, Cp2Ni-LiAlHi (1 1) can serve as a hydrogenation catalyst for reduction of alkenes it also reduces enones to ketones, but in low yield. In general, it is similar in reactivity to Raney nickel and to (2,2 -bi-... 

Hydroxydec-2-enoic acid 397 was identified in the fodder juice of the Weisel cells (gelee royale) of honey bees. One of the synthesis of 397 starts from suberic acid ethylester 393 222) which was first converted into the hydroxyacid 394 and then into the thiol ester 395. Raney nickel reduction of the latter yields an intermediate aldehyde which, in statu nascendi, reacts with the phosphorane 67 to give 396. Subsequent hydrolysis of396affords the ( )-a,0-unsaturated hydroxy acid 397 222) (Scheme 70). 

A new method for the transformation of a carboxyl group to a methyl group has been developed (123,124). In an intermediate step of this method, a thiol ester is cleaved with Raney nickel to the alcohol. The method may be outlined as follows ... 

Spero, McIntosh, and Levin (126) using W-l Raney nickel catalyst, in like manner converted a thiol ester to the alcohol, receiving also traces of aldehyde. With W-4 catalyst (127,128) the thiol ester (I) was rapidly... 

The thiol ester group can be removed, if necessary, by using Raney nickel, a good reducing agent for C-S bonds (see Chapter 46). Decarboxylation follows. 

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