Reductive desulfurization Raney nickel

Isothiazoles are reductively desulfurized by Raney nickel, e.g. as in Scheme 31 (72AHC(l4)l). 1,2,5-Thiadiazoles are subject to reductive cleavage by zinc in acid, sodium in alcohol, or Raney nickel, e.g. Scheme 32 (68AHC(9)107). 

When tribenzo[/>,with copper bronze and diethyl phthalate at 315°C for five hours, triphenylene (18) is obtained in 72% yield.4 Reductive desulfurization of 17 with Raney nickel in ethanol at room temperature gives l,l 2M -terphenyl (19) in 68% yield 4... 

Since these adducts undergo reductive desulfuration with Raney nickel, optically active aryl methyl sulfoxides are versatile reagents for the conversion of imines to optically active amines. 

The more generally known mercuric oxide-mercuric chloride hydrolysis 2 may also be used, and in the present case it gives a yield of about 90%. The reductive desulfurization of Part E is also based on the work of Mukaiyama.12 It is clearly superior to Raney nickel desulfurization, which gives only 36-45% of 3-benzylindole. 

Chrzanowska and Rozwadowska (60) performed a total synthesis of ( )-43, using amine 49 and the thioacetal of methoxycarbonylpiperonal (26) as substrates (Scheme 13). These two synthons were joined together under the influence of LDA, and the resulting addition product 50 was subjected to reductive desulfurization with Raney nickel to give racemic peshawarine (43). 

Fletcher, Hewitt G., Jr., and Richtmyer, Nelson K., Applications in the Carbohydrate Field of Reductive Desulfurization by Raney Nickel, V, 1-28... 

APPLICATIONS IN THE CARBOHYDRATE FIELD OF REDUCTIVE DESULFURIZATION BY RANEY NICKEL... 

Reductive desulfurization with Raney nickel is a reaction which requires but the simplest of techniques, is carried out under rather mild conditions and affords relatively good yields it is now. a standard and well-recognized reaction, having found use in practically all the various... 

For a brief review of the use of Raney nickel reductive desulfurization in organic chemistry in general see J. F. W. McOmie, Ann. Repts. on Progress Chem. (Chem. Soc. London), 40, 198 (1948). 

Reductive desulfurizations with Raney nickel have been conducted in absolute alcohol, aqueous alcohol, dioxane, and ether, the first two solvents being most frequently used. Presumably any neutral solvent, containing neither halogen nor sulfur and not readily reduced, could be employed. 

Reductive desulfurization with Raney nickel of the mercaptolysis products of streptomycin has supplied one of the keys to the elucidation of the structure and configuration of that antibiotic. Since the chemistry of streptomycin has recently been reviewed37 the reactions discussed here will be considered solely as examples of hydrogenolysis and their bearing upon the problem of the structure and configuration of streptomycin will be ignored. 

Thienothiophenes, like thiophenes and benzo[h]thiophenes, easily undergo reductive desulfurization with Raney nickel. The method was fvst applied in this series by Challenger et to determine the structures of 2-acetylthieno[3,2-h]thiophene and 2-acetylthieno[2,3-hl-thiophene the former gave 2-octanone (229), and the latter 5-methyl-heptan-2-ol (230) [Eqs. (75) and (76)]. 

An alternative synthesis from the Glaxo patents involves Fnedel-Crafts acylation of the 3-position of the indole intermediate 22 (Scheme 5) Reaction of hydrazine 10 with (phenylthio)acetaldehyde gave hydrazone 20, which was subjected to the Fischer indole reaction to give 3-thiophenylindole 21. It is noteworthy that this Fischer cyclization took place at room temperature because most require heat. Reductive desulfurization of 21 using Raney nickel provided indole 22. Acylation of the 3-position... 

Thiophenes have served as important four-carbon templates for molecular elaboration. Both functionalized cyclic and acyclic chains can be generated by carrying out conventional reactions on the thiophene nucleus and then performing a Raney nickel desulfurization at or near the very end of the scheme. Thus, the major constituent (279) of the Panamanian ant, Atta columbica, was made by Friedel-Crafts acylation of the thiophene derivative (277), followed by Grignard addition to the carbonyl group of (278), dehydration, and reductive desulfurization (Scheme 57) (60JOC1754). 

The chlorosulfonium compounds can also be used for the synthesis of oxindoles, the stable tautomeric form of 2-hydroxyindoles. The a -methylthio ketone is replaced by ethyl methylthioacetate and the products of the Sommelet-Hauser rearrangement are cyclized to 3-methylthiooxindoles. The methylthiooxindoles are reductively desulfurized with Raney nickel (equation 102) (74JA5508). 

One of the major uses of the thiophene ring in synthetic chemistry is based on its eventual destruction by Raney nickel. Synthetic manipulations on the intact thiophene ring (electrophilic substitution, metallation followed by reaction with electrophiles, etc.) are capable of producing precursors, which on reductive desulfurization can be transformed into a plethora of open-chain products, not easily accessible by other routes. The desulfurization reactions are usually carried out in methanol or ethanol (sometimes water) at 60-70 °C. Two excellent reviews of such transformations are available (62T21, B-74MI31400). 

Raney nickel reduction of 2-benzyl-5-ethylselenophene (71) yields 1-phenylheptane (72), a conversion analogous to the much used reductive desulfurization of thiophenes (73JGU871). The electrochemical reduction of selenophene-2-carboxylic acid gives a mixture of dimeric products the major product is compound (73). This is in contrast to the 2,5-dihydro derivatives obtained by electrochemical reduction of thiophene and furan carboxylic acids (82CS( 19)95). Wolff-Kishner reduction of 2-selenienyl 2 -thienyl ketone gives, in addition to the expected methylene derivative, 2-(pentenyl)thiophene (72ZOB1780). 

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