Thioethers aliphatic

The reaction of aliphatic and aromatic mercaptans with aziridines yields thioethers (117—119). 

Halothiophenes, which are not activated through the presence of —I—M-substituents, undergo substitution smoothly under more forcing conditions with copper salts in pyridine or quinoline. Hence 3-cyanothiophene and 5-methyl-2-cyanothiophene have been obtained from the corresponding bromo compounds. 2-Bromothiophene reacts readily with aliphatic cuprous mercaptides in quinoline at 200°C to give thioethers in high yields. The use of the copper-catalyzed Williamson synthesis of alkoxythiophenes from iodo- or bromo-thiophenes and alcoholate has been mentioned before. The reaction of 2-bromothiophene with acetanilide in nitrobenzene in... 

A variety of cleavage conditions have been reported for the release of amines from a solid support. Triazene linker 52 prepared from Merrifield resin in three steps was used for the solid-phase synthesis of aliphatic amines (Scheme 22) [61]. The triazenes were stable to basic conditions and the amino products were released in high yields upon treatment with mild acids. Alternatively, base labile linker 53 synthesized from a-bromo-p-toluic acid in two steps was used to anchor amino functions (Scheme 23) [62]. Cleavage was accomplished by oxidation of the thioether to the sulfone with m-chloroperbenzoic acid followed by 13-elimination with a 10% solution of NH4OH in 2,2,2-trifluoroethanol. A linker based on l-(4,4 -dimethyl-2,6-dioxocyclohexylidene)ethyl (Dde) primary amine protecting group was developed for attaching amino functions (Scheme 24) [65]. Linker 54 was stable to both acidic and basic conditions and the final products were cleaved from the resin by treatment with hydrazine or transamination with ra-propylamine. 

Ni11 complexes of various amine/thiophenolate ligands have been investigated (for Ni complexes of ortho-aminothiophenol see Section 6.3.4.9.2(iv)). Thiophenolate is expected to exhibit decreased bridging tendency compared to aliphatic thiolates, but complexes (466) and (467) still consist of two pseudo-octahedral NiL fragments bridged via thiolate donors. In contrast to the parent complex (466), the thiolate and thioether donors in (467) coordinate cis to the Ni center... 

Bi- and poly-thioethers with aliphatic backbones are produced by attack of RS on the appropriate haloalkane. This is the method of choice for RS(CH2)raSR (R = Me or Ph),26 MeC(CH2SR)3,27,28 MeS(CH2)raS(CH2)raSMe (n = 2 or 3) and MeS(CH2)raS(CH2) S(CH2) SMe.28,29 [Caution Some of these syntheses involve sulfur mustard derivatives as intermediates - these are very powerful vesicants and should be handled only with extreme care.] The other tridentates RS(CH2)3S(CH2)3SR (R = Et, Pr or Ph) may be obtained from nucleophilic attack by RS on the ditosylate TsO(CH2)3S(CH2)3OTs.30 Tetra-dentate thioethers involving o-phenylene interdonor linkages are also known.31 More recently the preparation and coordination chemistry of the silicon-apex derivative MeSi(CH2SMe)3 has been described.32... 

Aliphatic onium ions such as immonium, oxonium, and sulfonium ions have been introduced as even-electron ionic products of the a-cleavage occurring from molecular ions of amines, alcohols, and ethers or thiols and thioethers, respectively (Chap. 6.2.5). All these and analogous onium ions are capable of further fragmentation reactions, the majority of which are alkene losses [141] yielding fragments of high relevance for structure elucidation. 

The intermediacy of ion-neutral complexes is neither restricted to even-electron fragmentations nor to complexes that consist of a neutral molecule and an ion. hi addition, radical-ion complexes and radical ion-neutral complexes occur that may dissociate to yield the respective fragments or can even reversibly interconvert by hydride, proton or hydrogen radical shifts. Many examples are known from aliphatic alcohols, [180-183] alkylphenylethers, [184-187] and thioethers. [188]... 

Zappey, H.W. Ingemann, S. Nibbering, N.M.M. Isomerization and Fragmentation of Aliphatic Thioether Radical Cations in the Gas Phase Ion-Neutral Complexes in the Reactions of Metastable Ethyl Propyl Thioether Ions. J. Chem. Soc., Perkin Trans. 2 1991, 1887-1892. 

As for 2a-la dithia cation-radicals, they do not react directly with Oj. Aliphatic thioether cation-radicals as shown in Scheme 3.24 become capable of reacting with O2 only after the addition of hydroxyl anion (Schoeneich et al. 1993). 

In an earlier experiment, Jori et al. (14) reported that methionyl residues are important in maintaining the tertiary structure of lysozyme. The introduction of a polar center into the aliphatic side chain of methionine, as a consequence of the conversion of the thioether function to the sulfoxide, may bring about a structural change of the lysozyme molecule which, in turn, reduces the catalytic efficiency. When ozonized lysozyme was treated with 2-mercaptoethanol in an aqueous solution according to the procedure of Jori e al. (14), the enzyme did not show any increase in its activity. This may be explained in two ways. In one, such reactions are complicated by many side reactions, e.g. sulfhydryl-disulfide interchange, aggregation and precipitation of the modified enzyme (24-26). In the other, the failure to recover the activity of the enzyme may by associated with the extensive oxidation of other residues. 

In some cases involving aliphatic thiocarbonyl ylides, a 1,4-H shift occurs to afford vinyl thioethers. As an example, thiocarbonyl ylides (41), generated by the addition of isopropylidene carbene to aliphatic thioketones, are converted to divinylthioethers (42) (84) (Scheme 5.16). 

Famesylation of the Ras protein occurs at the C-terminal CAAX sequence (A aliphatic amino acid, X Ser or Thr). The famesyl residue is attached, with the help of a farnesyl protein transferase, via a thioether bond to the Cys residue of the CAAX sequence. Next, the last three amino acids are cleaved off by proteases and the carboxyl group of the C-terminal cysteine residue undergoes a methylesterification (Fig. 9.6). In addition, the Ras proteins have a palmitinic acid anchor at different Cys residues in the vicinity of the C terminus. The membrane localization of the Ki-Ras protein is also supported by a polybasic sequence close to the C terminus (see 3.7 and Fig. 3.12). 

S-oxidation. Aromatic and aliphatic sulfides, thioethers, thiols, thioamides, and thiocarba-mates may undergo oxidation to form sulfoxides and then, after further oxidation, sulfones (Fig. 4.23). 

Tetrahydrothiophene (88) has properties typical of aliphatic thioethers (e.g. diethyl sulfide) and is readily oxidized, both chemically and metabolically, to the sulfoxide (89) and sulfone (90). Incubation of (88) (5 p,mol) with rat-liver monooxygenases in the presence of appropriate cofactors results in the conversion of about 10% of the starting material to the sulfoxide in 30 minutes, whereas the sulfone is formed only in trace amounts (80UP10900). Incubation of the synthetic sulfoxide (89) under identical conditions affords the sulfone (90) in very... 

Other measurements on Zn11 and Cd" complexes include formation constants for aliphatic thioethers,848 and calorimetry with dithiodiacetate, S -thiodipropionate849 and phenylthioacetate.850... 

The simpler aliphatic sulphur derivatives considered in this section are the sulphur analogues of oxygen compounds, e.g. the thiols (RSH), and the symmetrical or unsymmetrical thioethers (R-S-R or R -S-R2). Compounds derived from these two groups, where the sulphur atom can attain a higher oxidation state, are the sulphinic and sulphonic acids (R-SO-OH and R-S02 OH), the sulphox-ides (R-SO-R), and the sulphones (R-S02-R). Other compounds of interest which are considered in the following discussion are ... 

To facilitate the nitro group displacement reaction, the thioethers 7, obtained by treatment of difluoride 6 with thiols, were oxidized with 3-chloroperbenzoic acid to afford the corresponding sulfones 8 (Fig. 4). The resulting sulfones 8 showed the expected high reactivity toward nucleophiles, as demonstrated by the efficient displacement of both the second fluoride and the nitro group with two different aliphatic amines to yield the highly substituted benzamides 10. 

In general, EC reactions are typically observed according to the following general rank order (by relative ease of oxidation) o,p-quinol and o,p-aminophenol > tertiary amine > m-quinol rv phenol rv arylamine > secondary amine thiol > thioether primary amines, aliphatic alcohols. (HDVs) each redox active metabolite are obtained from the response across adjacent EC-Array sensors. These data are a reflection of the kinetic and thermodynamic components of electron transfer reactions. Since chemical structure is a critical determinant of an analyte s redox behavior, the intrinsic generation of an HDV with EC-Array provides qualitative information for each species. 

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