Sulphides in Synthesis

Sulphides in Synthesis.—Applications of sulphides in synthesis making use of the potential nucleophilic properties conferred by the sulphur atom in alkyl or aryl alkyl sulphides are reviewed in the following chapter. 

Piotrowska, B. Serafin, and K. Wejroch-Matacz, Roezniki Chem., 1975, 49, 635. 

The formation of t-butoxy-dialkylselenonium chlorides from dialkyl selenides and Bu OCI has been studied.  

Further study has been made of the use of the methylthiomethyl group for protection of alcohols in synthesis. Primary and secondary alcohols and tertiary alcohols are converted into methylthiomethyl ethers using dimethyl sulphoxide and AcgO, and de-protection is brought about under neutral conditions with a mercury(n) salt. Under these conditions, a 1,3-dithian moiety or a silyl ether grouping in the same molecule are unaffected. Protection of alcohols as 2-phenylselenoethyl ethers and their de-protection by oxidation has been proposed.  

Simpler sulphides also have uses in synthesis. Diphenyl sulphide is proposed as a reagent for the cleavage of 1,2-dioxetans with rearrangement, and hydro-boration by BHg-MeaS in EtaO has been reported, hex-1-ene giving 94% hexan-l-ol and 6% hexan-2-ol after treatment of the intermediate trihexylboranes with alkaline HjOa.  

Sulphides in Synthesis.— This section is concerned with reactions of sulphides which may be exploited in carbon-carbon bond formation, or controlled introduction of functional groups, or for functional-group protection. 

Methods for the introduction of an a-alkylthio-group into an aliphatic ketone have been established, involving either treatment of the silyl enol ether derived from the ketone with MeLi and a sulphenyl chloride, or a-carbanion formation from the ketone with the Li salt of a secondary amine, followed by treatment with a disulphide or a sulphenyl halide.  

Yoneda, ibid., p. 4731 (c) Z. Yoshida, H. Konishi, Y. Tawara, and H. Ogoshi, J. Amer. Chem. 

Mukaiyama, K. Kamio, S. Kobayashi, and H. Takei, Bull. Chem. Soc. Japan, 1972,45,3723. 

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Activation of the adjacent proton at a-sp centres has been exploited in uses of sulphides in synthesis (see later section), and must be the basis for a novel acetoxyl-transfer reaction, (14) (15), that is observed in refluxing benzene... 

Formation of a symmetrical sulphide (a) (e.g. dipropyl sulphide, Expt 5.204), is conveniently effected by boiling an alkyl halide (the source of carbocations) with sodium sulphide in ethanolic solution. Mixed sulphides (b) are prepared by alkylation of a thiolate salt (a mercaptide) with an alkyl halide (cf. Williamson s ether synthesis, Section 5.6.2, p. 583). In the case of an alkyl aryl sulphide (R-S Ar) where the aromatic ring contains activating nitro groups (see Section 6.5.3, p. 900), the aryl halide is used with the alkyl thiolate salt. The alternative alkylation of a substituted thiophenol is described in Section 8.3.4, p. 1160. The former procedure is illustrated by the preparation of isobutyl 2,4-dinitrophenyl sulphide (Expt 5.205) from l-chloro-2,4-dinitrobenzene and 2-methylpropane-1-thiol. 

One of the first nucleophiles recognized to react under irradiation with Arl by the S l mechanism was PhS" ion, which has led to the synthesis of many aryl phenyl sulphides in liquid ammonia. Bromoarenes also react, but much more slowly270. 

The story of the evolution of life on Earth is relatively straightforward in comparison to the problem of how it first arose. The abiotic synthesis on Earth of the organic compounds necessary for the creation of life appears to require a reducing atmosphere (see Box 1.5). Early experiments with electrical discharges in mixtures of methane, ammonia and hydrogen sulphide in the presence of water created various organic compounds es-... 

For the synthesis of organylsilanethiols R3SiSH (725) a common approach is to employ chloro- or bromosilanes (724) with hydrogen sulphide in the presence of tertiary amines as hydrogen halide acceptor407-411 (equation 368). Without an HX acceptor no reaction occurs even SiCl4 reacts with H2S only above 500 °C to yield trichlorosilane-thiol412 (726) (equation 369). 

The two principle products from the addition of sulphur to Et2P(S)H are the phosphin-odithoic acid, Et2PSSH, and the trisulphane, 174 (R = Et, Z = Z = S, = 3)(Scheme 48), which can be separated wthout too much difficulty. In many cases, the phosphinodithioic acids may be isolated as the salt of a heavy metal such as nickel, but a better synthesis procedure consists in the addition of the sulphur to the secondary phosphine sulphide in aqueous alkali (ammonia solution provides better yields than sodium hydroxide), when the polysulphane—the principle by-product—is broken down under the influence of the alkali metal sulphide. A phosphinodiselenoic acid may be obtained in essentially the same... 

Reviews cover the topics alkynethiolates in synthesis " oxygen-exchange reactions of sulphoxides sulphonyldiazomethanes C—S bond cleavage acyl isothiocyanates radical reactions of sulphur compounds addition of sulphenyl halides to olefins " sulphenamidcs mercaptoethylation of amines sulphur as a chiral centre " stereochemistry of S and S " compounds " reductive cleavage of sulphides, synthetic uses of alkene- and alkyne-thiolates, and thio-Claisen rearrangements nucleophilic displacements at sulphur in disulphides aromatic... 

Important variants of procedure have been tested, providing wider possibilities for thio-Claisen rearrangements in synthesis like any other method for forming carbon-carbon bonds whose scope exceeds its limitations, there is the likelihood of studies of the type described in this Section being taken up in many more laboratories. Lithiation of allyl sulphides is followed by rearrangement, providing a very efficient method for the synthesis of thiols, alkyl sulphides, and hydrocarbons of the squalene type, or based upon the artemisyl skeleton. Typically, benzyl yy-dimethylallyl sulphide (65) gives (66) with four equivalents of... 

The 4 -thiapyran-4-thione route to thiathiophthens has been modified so as to yield 6a-selenahthiopthens (35). The intermediate selenoketones (38) are unstable, but react satisfactorily with sodium sulphide in aqueous dimethyl sulphoxide to give dianions which are oxidized, as in the original synthesis, with ferricyanide. N.m.r. data on 6a-selenathiophthen, and on its 3,4-dimethyl and 2,5-diphenyl derivatives, indicate real or time-averaged... 

The latter is polymerized to yield a water soluble sulfonium salt polyelectrolyte (28d) which is then purified by dialysis [135]. The precursor polymer is converted to PPV (28e) by the thermal elimination of dimethyl sulfide and HCl. The method has been later developed by Horhold et al. [136], Lenz et al. [137,138], Murase et al. [139] and Bradley [140]. One of the major improvements was the use of tetrahydrothiophene instead of dimethyl sulphide in the synthesis of the precursor polymer [141]. The use of the cyclic leaving group facilitates the elimination when the precursor polymer is heated at 230-300 °C and leads to PPV with reduced amounts of defect structures in the polymer chain. 

The use of a phase-transfer catalyst-aqueous sodium hydroxide system has now been employed in the synthesis of thiophenylcyclopropanes [e.g. (67)] from chloro-methyl phenyl sulphide. In like manner, the addition of chlorofluorocarbene to olefins works well in a two-phase system and has the advantage that olefins with base-... 

Books published recently include several that are wholly devoted to organosulphur compoundsand others " in which specific chapters are relevant to the coverage in this chapter. Reviews have appeared that deal with applications of organosulphur compounds in synthesis " (including uses of yff-keto-sulphides, vinyl sulphones, and vinyl sulphides ) and the synthesis of organosulphur compounds,sulphenyl compounds, indolethiols, allenic sulphides and sulphenamides, organosilyl sulphides, selenides, and tellurides, optically active... 

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