From Thiocarboxylic Acid 5-Esters

Sodium hydrogen sulfide Thiocarboxylic acid chlorides from dithiocarboxylic acid esters via dithiocarboxylic acids... 

Thiocarboxylic acid esters from a-chlorimmonium chlorides -e- s. 19, 628 ... 

Prepn. from N,N-disubst. carboxylic acid amides—Thiocarboxylic acid esters Dithiocarboxylic, thiolic, and thionocarboxylic acid esters—Ring closures to heterocyclics s. 19, 628 a-chlorimmonium chlorides cf. M. Grdini6 and V. Hahn, J. Org. Chem. 30, 2381 (1965)... 

Thiocarboxylic acid esters from a-chlorimmonium chlorides... 

Scheme 3 Amino Acid Thioesters by Active Ester Coupling or from Thiocarboxylic Acids113-161 rl — ...------- R1...

DCC can be used to prepare 5-alkyl and 5-aryl thiocarboxylates (1) from carboxylic acids and thiols according to equation (5). This method has been successfully applied to the synAesis of thiol esters with sensitive substituents, e.g. 5-methyl thioacrylate, a natural product. In particular, N-protected amino acid and peptide 5-phenyl esters, which are useful building blocks in peptide synthesis, are obtained in excellent yields without racemization. N-Hydroxyphthalimide and DMAP have been used as cocatalysts to facilitate the reaction. The preparation of the Wittig reagent (5) by this route is shown in equation (6). 

Methyl and S-aryP thiocarboxylic esters can also be prepared directly from carboxylic acids if thiocyanates or chlorothioformates are used instead of thiols (equations 11 and 12). 

An acyl transfer agent which can be used for the synthesis of acid anhydrides is obtained from the reaction of an acid chloride with 4-benzylpyridine (equation 24). In this way benzoic acid anhydride and cinnamic acid anhydride were obtained in 72% and 57% yields, respectively. As the intermediate, 1-acyl-4-benzylidene-l,4-dihydropyridines, can be isolated, Ais procedure should be well suited for the preparation of mixed anhydrides. Mixed aromatic and aliphatic anhydrides can be prepared with 2-ben-zoylthio-l-methylpyridinium chloride and salts of carboxylic acids. These reactions are carried out in aqueous solution. Iliey make use of the high reactivity of esters of thiocarboxylic esters towards nucleophiles. The mixed anhydrides of benzoic acid with 3-phenylpropanoic acid, phenoxyacetic acid, isobu-tyric acid, p-toluic acid and cinnamic acid were formed in 82, 79,61,91 and 66% yields, respectively. 

Thallium(l) thiolates have been introduced by Masamune et Their use is especially advantageous if 5-t-butyl thiocarboxylic esters are to be prepared which can serve as educts for macrolide synthesis. Zearalenone dimethyl ether ethylene acetal (22 cf. also Scheme 1) was obtained from the corresponding acid chloride and thallium(I) a-methylpropanethiolate via the S-f-butyl benzenecarbo-thioate (21 equation 14)... 

Synthesis of Thiono- and Dithio-esters.—Alkylation of Thio- and Dithio-carb-oxylates. Alkylation of thiocarboxylates takes place at the sulphur atom, and thiolesters are the reaction products in almost all cases. The reaction of thio-benzoic acid with diazomethane yields, however, some methyl thionobenzoate, along with a ten-fold amount of the thiolobenzoate, from which it may be cleanly separated by chromatography, On the other hand, silylation of monothio- or monoseleno-carboxylates affords the 0-silyl esters, in contrast to germylation or stannylation, which occur at the sulphur atom. 

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