Acylation of thiols

Entry 1, Table 13.17), the acylation of support-bound thiols (Entries 2 and 3), and the acylation of thiols with support-bound carboxylic acids (Entry 4, Table 13.17). Thiol esters are stable towards acids (e.g. 50% TFA in DCM), but are readily cleaved by nucleophiles and are reduced to alcohols by treatment with LiBH4 [170]. 

Acylation of Thiols with Anhydrides, Ketenes and Esters... 

Acid anhydrides in the presence of basic catalysts can be used instead of acyl chlorides in acylation reactions of thiols.Mixed anhydrides of N-protected amino acids and ethyl carbonate yield the corresponding S-f-butyl thiocarboxylic esters, which are useful reagents for peptide syntheses (equation 22). Acylation of thiols with ketenes (equation 23) is a method of long standing. In many cases the yields are nearly quantitative. Functionalities such as acetamino groups or carbon-carbon double bonds in the thiol are not attacked under the mild reaction conditions and optically active thiol esters are obtained without racemization. 3 ... 

Thioacyl halides are not easily accessible. Aliphatic derivatives, in particular, can only be isolated in rare cases. Thioacylations of alcohols are therefore less important as synthetic methods than acylation of thiols with acyl hdides. Nevertheless, a variety of 0-alkyl and 0-aryl arenecarbothioates (2) have been obtained according to equation (4i).6.i4,25,2s... 

S-Esters of thiocarboxylic acids are obtained on acylation of thiols this reaction, which is often very smooth even in the absence of a base,335 is generally carried out by the Schotten-Baumann technique336,337 or in the presence of pyridine.338... 

Esters of thiocarboxylic acids are formed on acylation of thiols by acid anhydrides. For the preparation of the lower 5-esters the following Schotten-Baumann procedure is used 430,431... 

In addition to acylation of thiols by carboxylic acids activated by GDI which is described in the previous section, other reactions were used for sulfur bond construction in ball-milling conditions. Several reaction cascades which are given in this section start with the formation of sulfur bond. 

In addition, nonenzymatic acylation of cysteine thiols on proteins incubated in the presence of acyl-CoA has been described, although the biological importance of this process is still unclear. 

Unsaturated acyl derivatives of oxazolidinones can be used as acceptors, and these reactions are enantioselective in the presence of chiral to-oxazoline catalysts.321 Silyl ketene acetals of thiol esters are good reactants and the stereochemistry depends on the ketene acetal configuration. The Z-isomer gives higher diastereoselectivity than the Zf-isomer. 

Carboxylic acid esters of thiols are considerably more reactive as acylating reagents than the esters of alcohols. Particularly reactive are esters of pyridine-2-thiol because there is an additional driving force in the formation of the more stable pyridine-2-thione tautomer. 

Furakawa et al. (1978) have suggested that the reaction of benzyl a-toluenethiolsulfinate shown in (71) proceeds through a mechanism (72) where there is an initial cycloelimination, followed by a recombination of PhCHjSOH and PhCH=S to give an or-sulfinylthiol, and then subsequent acylation of the thiol group. 

Upon acylation of the copper complex with benzoyl chloride the corresponding 5-benzoylthio-1,2,3,4-thiatriazole is formed. The reaction product is (apparently) incorrectly assigned by the authors to 4-benzoyl-1,2,3,4-thiatriazole-5-thione based upon comparison with the product obtained from direct acylation of thiatriazol-5-thiol and citation of the older incorrect structure assignments. The thiothiatriazolato-copper(I) complexes are formulated as Cu-N(4) complexes. However, this assignment is based upon an IR band at 1200 cm attributed to a thiocarbonyl group, again upon comparison with the older literature. Further characterization therefore seems necessary. 

---