Thiols thiocarbonylation

The kinetics of the xanthation of sucrose were studied in the same year by Cherkasskaya, Pakshver, and Kargin, who determined potentiometric-ally the concentrations of the dithiocarbonate derivative and also of inorganic sulfide and trithiocarbonate. The rate of formation of 0-(sodium thiol-thiocarbonyl)sucrose was found to pass through a maximum with increasing alkali concentration, presumably due to a shift of the equilibrium in favor of side reactions in strongly alkaline solution. This result appears to parallel the qualitative findings of Lieser and Hackl for polysaccharides. 

The thiation procedure described here is an example of a general synthetic method for the conversion of carbonyl to thiocarbonyl groups. Similar transformations have been carried out with ketones, carboxamides,esters,thioesters, 1 actones, " thiol actones, - imides, enaminones, and protected peptides. ... 

Tc(V) and Re(V) are thiols, thioethers and thiocarbonyl compounds and molecules containing combinations of their functional groups. There exist significant differences in the ability of the various groups to form stable complexes and in the kind of complexes formed. Unlike thiols, a neutral S-donor shows a preference for the metals in oxidation states lower than +5. 

Oxidation with bis(p-methoxyphenyl) telluroxide (general procedure All the reactions are performed at room temperature under Nj in CHCI3 or CHjClj. Approximately 10 mL of solvent is used for every 100 mg of substrate. For thiocarbonyl derivatives, 1.1 equiv of the reagent is used, for thiols 0.55 equiv. The mixtures are concentrated by evaporation and submitted to thin layer or column chromatography to isolate the products. An2Te is always recovered in a yield of 64-96%, while sulphur or selenium is always recovered in near quantitative yields from reaction with thio- or selenocarbonyl derivatives. 

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. 

Acidic compounds of type R—XH, which are able to protonate thiocarbonyl ylides, also undergo 1,3-addition leading to products of S,S-, S,0-, or 5,A-acetal type (Scheme 5.20). Thiophenols and thiols add smoothly to thiocarbonyl ylides generated from 2,5-dihydro-l,3,4-thiadiazoles (36,38,86,98,99). Thiocamphor, which exists in solution in equilibrium with its enethiol form, undergoes a similar reaction with adamantanethione (5)-methylide (52) to give dithioacetal 53 (40) (Scheme 5.21). Formation of analogous products was observed with some thiocarbonyl functionalized NH-heterocycles (100). 

Bei der Umsetzung von Carbonsaure-hydraziden mit Schwefelkoblenstoff und Alkylhalogeni-den erhalt man l-Acyl-2-(alkylthio-thiocarbonyl)-hydrazine197. Diese cyclisieren unter Alkan-thiol-Abspaltung, z.B. thermisch zu 2-Mercapto-l,3,4-oxadiazolen (vgl. S. 544). Praparativ bietet diese Methode gegeniiber der Cyclisierung von Carbonsaure-hydraziden mit Schwefelkohlenstoff keine Vorteile. 

Besides alkoxy-, amino-, and amidocarbonylation reactions, a carbonylation process using a thiol as nucleophile, that is, thiocarbonylation, has been extensively studied.It has been shown that the thiocarbonylation takes place with 1-alkynes, " " " propargyl alcohols,allenes, " 1,3-dienes, propargylic mesylates, " and bicyclopropylidene . 

The more favourable equilibrium constants for the addition of thiols to the carbonyl group of aldehydes and ketones compared to those for the addition of alcohols are well documented (Jencks, 1964 Lienhard and Jencks, 1966 Kanchuger and Byers, 1979), if not fully understood. There appears to be a similar tendency for thiols to add to the carbonyl (or thiocarbonyl) group of esters (or thioesters) and several tetrahedral intermediates with one or more... 

A facile route to isothiochromans involves the base-catalyzed reaction of a benzyl dibromide with an a-thiocarbonyl compound. The method has been extended to the synthesis of an anthraceno[2,3-f]thiopyran, a heterocyclic analogue of an anthracyclinone (Equation 169) <1994S363>. In like manner, alkylation of the 2-aryl-1-bromoethane 491 by thiourea and subsequent liberation of the thiol function creates an isothiochroman precursor. An intramolecular Michael addition to the cr, )-unsaturated ester side chain yields the 1-substituted heterocycle (Scheme 179) <1992JOC1727>. 

The enzymatic reduction of a thiocarbonyl compound has been investigated [159] for the first time, in order to provide a new route for enan-tiopure thiols, molecules which are currently needed for asymmetric synthesis. Reaction of easily available /1-thioxoesters with baker s yeast under classical conditions did furnish the expected thiols, but with lower enantiomeric purity and moderate conversion rate, due to the competitive hydrolysis of the thioxo group into a carbonyl leading to an alcohol. However, conditions (ethyl acrylate, dry yeast) were found to improve the production of (S)-ethyl 3-mercaptobutanoate. Cyclic thioxo esters led to high stereoselectivity of cis (1S,2S) products, but with moderate chemical yields. 

Exceptions to the carbophilic addition of heteronucleophiles to thiocarbonyl compounds were demonstrated with thiols and thioaldehydes [160] or dithioesters [36] bearing an a-electron withdrawing group, which undergo selective thiophilic addition. 

Bis[4-methoxyphenyl] tellurium oxide was found to be a mild and highly selective oxidizing agent for the conversion of thiocarbonyl groups to carbonyl groups, thiols to disulfides, arylhydrazines to arenes, and 1,2- or 1,4-dihydroxyarenes to quinones. No reaction was observed with simple phenols, alcohols, enamines, amines (including pyrrole, indole, tryptophan, tyrosine, aniline, and dimethylaniline), oximes, dithiolanes, isonitriles, and 2,4-dinitrophenylhydrazones4. 

There is apparently only one report of the dissolving metal reduction of thioketones thiobenzophe-none (107) has been reduced with excess Na-THF to give dianion (108), which on acidification gave thiol (109). The thiol was not isolated, but was oxidized with iodine to give the corresponding disulfide in 65% overall yield. The mechanism of the reduction is suggested to be the sequential addition of two electrons to the thiocarbonyl, which was confirmed by electron spin resonance spectroscopy studies of the intermediate thioketyl, and trapping dianion (108) with a variety of electrophiles. ... 

In the last decade the methods of converting carbonyl to the corresponding thiocarbonyl compounds have been substantially improved. " Therefore, thioxo- as well as dithio-carboxylic esters are accessible from esters, thiol esters and even carboxylic acids by reacting them with phosphorus pentasul-fide or 1,3,2,4-dithiadiphosphetane 2,4-disulfides such as Lawesson s or Davy s reagent (equation 4 cf. Chapter 4.1, this volume). 

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