Thiols and thioethers

Thioethers are said to be conveniently prepared from alcohols under mild conditions by reaction with sulphenimides such as (70) in the presence of tri-butylphosphine [equation (17)]. Both the succinimide and phosphine oxide by- 

Full details have been published this year of the synthesis of allyl phenyl sulphides by acid-catalysed rearrangement of /8-phenythio-alcohols [(71)- (72)]. 

Several new methods for the reduction of sulphoxides to sulphides have appeared. Trifluoroacetic anhydride has been used in conjunction with dimethyl sulphide, hydrogen sulphide, or sodium iodide. The silicon compounds bromo- and iodo-trimethylsilane, or the phenyltrimethylsilane-iodine combina- 

Tanikaga, K. Nakayama, K. Tanaka, and A. Kaji, Chem. Letters, 1977, 395. 

Reactions.—Full details are now available of the photochemical and thermal [1,3] phenylthio shifts of allyl phenyl sulphides [(73)- (74)]. Oxidation of such sulphides can lead to allyl alcohols through the known sulphoxide-sulphenate equilibrium with sulphenate trapping. 

2-Tetrahydrofurany1- and 2-tetrahydropyranylthiomethy1-lithium (2 ) have been used as methanethiol carbanion equivalents. 

Aromatic iodides may be converted into thiophenols by nickel(O)-catalysed reductive coupling with thiourea followed by alkaline treatment of the intermediate salt and liberation of the desired product on acidif ication. Reaction of organocuprates with 

Unsymmetrical thioesters have been obtained in good yields by 

Thioacetals have been converted into -keto-sulphides by reaction 

Allylic sulphides have also been prepared by reaction of thio- 

Benzylic alcohols have been converted directly to benzyl alkyl sulphides by treatment with an organic disulphide and Primary amines can be trans- 

New reagents for the sulphoxide to sulphide reduction are trimethylsilyl chloride-sodium bromide (MeaSiBr in situ), trimethylsilyl chloride-zinc, and t-butyl bromide.  

H0CH2-fCH20CH2 CH20H CH2=CMeCH20CH2-fCH20CH2 CH20H 

Transesterification in the presence of a templating metal cation has been used to prepare some tetra-ester polyether macrocycles from dimethyl malonate [equation (16)], and intramolecular transesterification of (75) is one of the 

Tazaki, H. Nakamura, M. Takagi, and K. Ueno, Chem. Lett., 1981, 1583. 

Sulfur is in the same group of the periodic table as oxygen and forms compounds structurally similar to alcohols. Compounds containing an —SH group, called a sulfhydryl group, are named as mer-captans or thiols. The nomenclature of these compounds resembles that of alcohols, except that the suffix - thiol replaces the suffix -ol and the -e of the alkane name is retained. 

For example, the polycyclic disulfide shown in Fig. 7 was calculated to have the structure (a), which is what is found crystal-lographically (Wahl et al., 1975) rather than the alternative structure (b). Since it is known that the torsional angle preferred about the 

S—S bond is approximately 90°, it had been supposed that structure (b), where the torsional angle is 100°, would be favored over (a), 

It is known that the axially protonated form of thiacyclohexane is the stable conformation and the same is true in the corresponding selenium case (Allinger and Hickey, unpublished Hickey, 1973). The that the axial proton is favored because of attractions between it and the axial hydrogens in the 3- and 5-positions. 

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S-Linked Substituents (Sulfonic Acids, Thiols and Thioethers)... 

Thiols and thioethers, both alkyl and aryl, can be desulfurized by hydrogenolysis... 

Note Sulfldes, thiols and thioethers also react. The blue background of the chromatogram treated with the reagent sequence fades with time. 

Scheme 5. Synthesis of thiol and thioether fimctionalized primary phosphines 11 and 12... 

We distinguished between alcohols and ethers and between thiols and thioethers, and so we will consider the three relevant exchange quantities for amines, one apiece for primary, secondary and tertiary species. For each exchange reaction, all species are in the... 

The importance of chiral thiols and thioether linkages in biological systems has prompted intense investigation of the use of chiral amines [see e.g. 5-11] and ammonium salts [see e.g. 12] as agents for asymmetric induction in the Michael-type addition reaction. Considerable success has been achieved using chinchona alkaloids and their A-alkyl derivatives (see Chapter 12). 

The El mass spectra of thiols and thioethers also show a series of onium ions generated by a-cleavage of the molecular ion (Table 6.9). Sulfonium ions can easily be recognized from the isotopic pattern of sulfur (Fig. 6.9). The fragmentation patterns of thioethers will be discussed in greater detail later (Chap. 6.5.2 and 6.12.4). 

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. 

Aryl thiols and thioethers can be prepared in reactions similar to 3-1 and 3-4.87 Activated aryl halides generally give good results, but side reactions are occasionally important. Diaryl... 

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 ... 

Hydroxy Thiols and Thioethers 0-35 Reaction between epoxides and NaSH... 

If the target molecule is monofunctional, the disconnection process is classified as a one-group disconnection. The bond initially considered for cleavage would be, if present, the a-carbon-heteroatom single bond (i.e. the C—O, C—X, C—N, C—S bonds) as would be found in, for example, alcohols (Section 5.4), alkyl halides (Section 5.5), ethers (Section 5.6), nitroalkanes (Section 5.15), amines (Section 5.16), thiols and thioethers (Section 5.17). 

Begin to recognize the important functional groups alkene, alkyne, alcohol, ether, aldehyde, ketone, carboxylic acid, ester, amine, nitrile, amide, thiol, and thioether. 

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