Arene thiols

Unprotected sugar Ac20, acid, arene thiols [21-23]... 

High yields are achieved with alkane thiols, but to ensure good results with arene thiols, CaCOj is employed as acid captor instead of lutidine, avoiding the side reaction forming disulphides. 

Table 13 Reaction of Pyridine 1-Oxides with Alkene- and Arene-thiols tRSH)...

In contrast, because of similar electronegativities, the transition state for hydrogen transfer from benzene thiol to a perfluoro-n-alkyl radical should have little polar character. In confirming the important role of polar effects in these hydrogen transfer processes, a good Hammett correlation was observed for the reduction of n- c7f15i by a series of arene thiols [141,143]. 

The contribution of polar structures reduces the barrier and also the intrinsic barrier. This results for non thermoneutral reaction in a reduction of isotope effect. This has been a controversial subject for several years it is extensively covered by Russell29. The variation with substituents in the low isotope effects for the reaction of aryl radical with arene thiols were explained using such an effect. We may possibly further account for the lower intrinsic barrier for the R-H-Cl system (3.8 Kcal) than for the R-H—S system (5 Kcal) in terms of the greater electronegativity of chlorine. 

Solvolysis products 59, 156b, and 161 were explained (Scheme 41 <1998BCJ1187>) as a result of solvent addition to carbenium ion 160. Addition of water leads to arene thiol as a final product. Its reaction with two... 

An alternative method for the preparation of a kinetic zinc ketone enolate (123) from an arene thiol ester 121 and bis(iodozincio)methane (122) in the presence of a palladium(O) catalyst was developed by Matsubara and coworkers (equation 36) . The modest reactivity of the zinc reagent 122 makes this transformation highly chemo- and regioselective neither isomerization of the kinetic enolate 123 nor a palladium-catalyzed coupling with the thiol ester 121 could be observed. Thus, treatment of zinc enolate 123 with various aldehydes or ketones led regioselectively to one aldol product 124. The method provides access to reactive functionalized zinc enolates which are otherwise hard to obtain. 

There are some 3,000 publications reporting calixarenes, many of which can be obtained by searching databases under the term calix. In addition, several books have been written on calixarenes, and metal complexes are described in all of them.1-6 Reviews on metal complexes of calixarenes has been published,7-10 and a book published in 2001 also makes numerous references to them.11 Among the other calixarenes are the calix[4]arene thiol (7) and the thiacalix[4]arene (8). Related compounds are the oxacalix[3]arene (9) and the azacalix[3]arene (10), both of which have been used as complexants for metal ions. 

Guimoe recently demonstrated the addition of thiols to electron-deficient alkenes using well-defined Cu-NHC thiolate complexes (31) [255, 256]. The prehminary scope is broad, with a number of potentially reactive electron-withdrawing groups being well-tolerated. Both alkane thiols and arene thiols are effective. In addition, sterically hindered olefins also react efficiently. 

The stericaUy hindered 2,4,6-trimethylphenol also worked weU, but ahphatic alcohols did not react weU with arynes under the reaction conditions. On the other hand, arene thiols reacted well with arynes, affording the desired S-arylated products in fairly good yields (Equation 12.10). 

The asymmetric a-sulfenylation of ketones is a particularly challenging reaction, as demonstrated by the poor success reported in the stereoselective variants via classical enolate/azaenolate reaction with an electrophilic sulfur reagent [71]. An umpolung approach has been devised by Coltart and co-workers [72] to effect the first asymmetric a-sulfenylation of ketones with arene thiols. Nitroso alkene derivatives, in i/tM-generated under basic conditions from a-chloro oximes, reacted with arene thiols in the presence of cinchona thiourea 27, which promoted the conjugate addition of thiophenol (Scheme 14.25). The chiral nonracemic a-sulfenylated oximes were directly hydrolyzed by IBX to ketones in high yield and good enantioselectivity. 

We reported that commercially available a,a-L-diphenyl prolinol 17d promoted the desymmetrization of wejo-aziridines with arene thiols (Scheme 14.30) [90]. A -Aroyl protected aziridines were converted into the product in good yield and moderate ee. 

SCHEME 14.29. Pase transfer and quinine catalyzed desymmetrization of wcio-aziridines with arene thiols. 

The activation of the reagents has been supposed to occur via deprotonation of arene thiol by catalyst 32 to give a sterically encumbered ion pair, whereas the... 

SCHEME 14.31. Desymmetrization of meso-azindines with VPA/TMSSPh and VPA/arene thiol systems. 

SCHEME 1432. Desymmetrization of /neso-aziridines with a guanidine/arene thiol system. 

The hypothesis that the amine-catalysed oxidation of thiols is a particular case of the more general reaction of oxidation by molecular oxygen of thiolate ions is confirmed by the finding that arene-thiols, which are more acidic and hence more dissociated, are oxidized faster than arylalkane-and alkane-thiols in the presence of amines . 

Sato A, Yorimitsu H, Oshima K. Radical additions of arene-thiols to ynamides for the selective synthesis of A-[(Z)-(aryl-sulfanyl)-l-alkenyl]amides. Bull. Korean Chem. Soc. 2010 31 570-576. 

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