Thiophenols alkylation

It is used as a dispersion agent to prevent polymerization or product decomposition taking place when an uncontrolled temperature rise occurs in the course of an exothermic reaction. In turn, it also plays the role of a diluent as solvent but with unquestionable benefits in cost and safety for example, reduction of carbonyl compounds [Eq. (26)] [50], indole acylation [Eq. 27)1 [511, and thiophenol alkylation [Eq. (28)] [52]. 

Alkyl mercaptans are partly soluble in solutions of caustic alkalis, but their salts are hydrolysed in dilute aqueous solution back to the free mercaptans. Thiophenols are soluble in alkah hydroxide solutions. Upon treatment with sodium, hydrogen is evolved. 

Organosulfur Adsorbates on Metal and Semiconductor Surfaces. Sulfur compounds (qv) and selenium compounds (qv) have a strong affinity for transition metal surfaces (206—211). The number of reported surface-active organosulfur compounds that form monolayers on gold includes di- -alkyl sulfide (212,213), di- -alkyl disulfides (108), thiophenols (214,215), mercaptopyridines (216), mercaptoanilines (217), thiophenes (217), cysteines (218,219), xanthates (220), thiocarbaminates (220), thiocarbamates (221), thioureas (222), mercaptoimidazoles (223—225), and alkaneselenoles (226) (Fig. 11). However, the most studied, and probably most understood, SAM is that of alkanethiolates on Au(lll) surfaces. 

When thionyl chloride is used, diaryl sulfoxides are usually the main products. Unsymmetrical diaryl sulfides can be obtained by treatment of an aromatic compound with an aryl sulfenyl chloride (ArSCl) in the presence of a trace amount of iron powder.Aromatic amines and phenols can be alkylthiolated (giving mostly ortho product) by treatment with an alkyl disulfide and a Lewis acid catalyst. With certain substrates (primary amines with a chloro group, or a group not replaceable by chloro, in the para position), treatment with S2CI2 and NaOH gives thiophenolate salts ... 

The hydrothiolation of terminal alkyl alkynes with 96 (Fig. 2.17) proceeds with good degree of regio- and chemo-selectivity, especially with thiophenol and p-methoxy-thiophenol as substrates. Isomerisation to the internal alkenyl thiolates accounts for less than 9% of the thiolated products under the reaction conditions. In addition, further hydrothiolation of the vinyl thioether product is not observed. Typical conversions of 70-85% at 1 mol% loading at 80°C within 5 h are observed. Arylthiols substituted with electron-withdrawing groups afford lower conversions. 

The second cycloaddition substrate took to form of 91 (Scheme 1.9b), incorporating a vinyl sulfone dipolarophile. Beginning with cyano ketone 84, which was readily prepared from 1,5-dicyanopentane via a previously reported three-step sequence [45], condensation with thiophenol produced vinyl sulfide 85 in 84 % yield. Vinyl sulfide 85 underwent bromination in acetonitrile to afford bromo-vinyl sulfide 86 (86 %), which was then treated with isopropylmagnesium chloride [46] to effect metal-halogen exchange affording an intermediate vinyl magnesium bromide species. Subsequent alkylation with Mel in the presence of catalytic CuCN provided the alkylated vinyl sulfide 87 in 93 % yield. The nitrile within vinyl... 

Peptides typically are prepared for this ligation process using a-alkyl thioesters, because they are simple to make at the time of peptide synthesis. However, due to the relatively slow reaction kinetics of alkyl thioesters, most native chemical ligation processes have been catalyzed through the use of thiol compound additives, such as benzyl mercaptan or thiophenol (Dawson et al., 1997). These compounds react with the initial a-alkyl thioester to form another intermediate, an aryl thioester, which is more reactive toward the N-terminal cysteine on the other peptide to be coupled. A study... 

An attractive feature of this route is that the macrobicyclic intermediate 40a can be readily N-alkylated without affecting the masked thiolate functions (209). Thus, reductive methylation of 40a with formaldehyde and formic acid under Eschweiler-Clarke conditions, followed by deprotection of 40b with Na/NH3 provides the otherwise inaccessible N6S2 ligand H2L19 in nearly quantitative yield (Scheme 1). Several other aza-thioethers 40c-p and their corresponding thiophenolate ligands were prepared by this route (see Fig. 30 and Table I) and some of them will be discussed further in later sections (210-215). 

It is well-established that the molecular and electronic structures of metal complexes of azamacrocycles are greatly affected upon N-alkylation (197). This is mainly due to two factors (a) the decrease of the ligand field strength and (b) the increase in the steric requirements upon going from a secondary to a tertiary amine donor function (251). To examine whether the properties of the dinuclear amine-thiophenolate complexes are affected by the N-alkyl substituents, analogous complexes of the... 

The reactivity of seven resin-bound thiophenol esters toward n.-butylamine (41) varied depending on their structures. The reaction of aromatic thiophenol esters (resins (34-36) took about 24 h to complete as indicated by the complete disappearance of carbonyl band in single bead FTIR spectra. On the other hand, the same reaction with alkyl thiophenol esters (resins 38-40) went to completion in less than 8 hours. The reaction with benzimidazolecarboxylic thiophenol ester (resin (37) was the fastest, finished in 3 h. 

When n-butylamine was used for cleavage, the rate of the alkyl thiophenol esters were approximately 13 times faster than that of the aromatic thiophenol esters. The rate of benzimidazolecarboxylic thiophenol esters was 45 times faster than that of aromatic thiophenol esters and 3 times faster than that of the alkyl thiophenol esters. 

The reactivity of seven resin-bound thiophenol esters toward 3,4-dimethoxy-phenethylamine (42) was consistent with the trend seen in n-butylamine cleavage reactions i.e. benzimidazole > alkyl > aromatic. However, the rate constant for the same thiophenol esters with 3,4-dimefhoxyphenethylamine was decreased by two to three fold compared with that with n-butylamine. The rate constant of ben-... 

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