Thiols as nucleophiles

Second-order rate constants have been reported for reactions of thiolates with l-aryl-2-halogeno-alkynes, and with 3-bromo-2(or 4)-nitro-4(or 2)-substituted thiophens, showing in the latter case that the conjugative effect from C(2) is greater than that from C(4) in thiophen. These examples illustrate the study of structure-reactivity relationships in organic halides, 

Preparative uses of thiolates, quite apart from syntheses of other sulphur functional groups discussed elsewhere in this Volume, include the demethyl-ation of aryl methyl ethers with EtS in hot DMF, and a similar use of thiophenol for demethylating aza-heterocyclic O-methyl ethers, of type =N—C(OMe)=. 2-Methylthio-l-methylbenzimidazole does not react with thiophenol, though an alternative reaction path is available for certain hetero-aryl methyl sulphides (17).  

Equilibrium constants for the reactions of cysteine derivatives with formaldehyde, and proton dissociation constants for the eight species of cysteine which exist in solution within the pH range 0—14, provide essential background information for evaluating the complex pH-rate profile for the formation of L-thiazolidine-4-carboxylic acid (18) from L-cysteine and formaldehyde.  

Thi as Nudeo rtiiles.— Aryl-oxirans yield mixtures of 1- and 2-aryl-2-phenylthioethanols with PhSNa, proportions being determined by substituents on the oxiran. Glutathione is not more nucleophilic than simple thiols towards benzene oxide, thus disposing of a theory that this tripeptide has a special detoxification function for arene oxide intermediates 

Photostimulated reactions of thiolates with iodobenzenes in liquid NHg, leading to sulphides in good yields, proceed through RS + Arl - RSAr R + 

ArS - mixed sulphides, indicating the operation of an aromatic iSknI reaction.  

Conditions have been worked out for the synthesis of methyl polyfluoroalkyl sulphides and 2-bromo-l,l-difluoroethyI phenyl sulphide by halogen-substitution reactions involving sodium thiolates. / -Nitrothiophenol reacts with 1,2-dichlorohexafluorocyclopentene to give the l,2-bis(p-nitrophenylthio)-analogue. Aryl alkyl tellurides PhTeR and bis(phenyltelluro)methane PhTeCHgTePh can be obtained from PhTeLi and an alkyl halide, or di-iodomethane, respectively. 

The nucleophilicity of thiols towards an sp ester carbon atom has previously been little studied. A detailed report has appeared showing that rates of reaction of substituted arenethiols with p-nitrophenyl acetate can be correlated with pJlTa values of the thiols, after substantial solvent effects have been taken into account this is a key reference for this area.  

5 N2-Type processes are involved in the ring-opening reactions of oxirans, under mild conditions (by thiols, adsorbed on alumina), and in the ring-closure of a penicillin-derived enethiolate.  

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A three-component domino reaction of isobutyral-dehyde, N-benzylidene aniline and pyridine-2-thiol as nucleophile gives access to 1,2,3,4-tetrahydroquino-lines as shown by Annunziata et al..161... 

Besides alkoxy-, amino-, and amidocarbonylation reactions, a carbonylation process using a thiol as nucleophile, that is, thiocarbonylation, has been extensively studied.It has been shown that the thiocarbonylation takes place with 1-alkynes, " " " propargyl alcohols,allenes, " 1,3-dienes, propargylic mesylates, " and bicyclopropylidene . 

Thiols are generally regarded as better nucleophiles than alcohols in substitution reactions. Accordingly, Hongmei Li investigated the use of thiols as nucleophiles in... 

M.E.Pende in S. Patai, Thiols as nucleophils, Vol. 15, S. 721, Interscience Publ., New York London 1974. 

Activation provided by the sulfur may also account for the extremely easy displacement of iodine from the thiophene 2-position, using aUcyl- or aryl-thiols as nucleophiles. ... 

Antilla et al. have described the phosphoric acid (234) that catalyzed, highly enantioselective ring-opening of meso A-acyl aziridines (235) with a series of functionalized aromatic thiols as nucleophiles (Scheme 65). ... 

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