Conversion of thiocarbonyl group

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. 

Two new procedures for the conversion of thiocarbonyl groups into the corresponding carbonyls (C=S to C=0) consist of sodium hydroxide... 

First reports have appeared on preparations of telluroesters (137) and telluroamides (138) both classes of compound are reasonably stable. The telluroxide (139) is useful for the conversion of thiocarbonyl groups into their oxo-analogues. The reagent exhibits considerable selectivity and, for example, does not oxidize phenols, alcohols, or many nitrogen-containing functions. ... 

The carbonyl group in 241 and 242 can be converted into thiocarbonyl which in turn is attacked by hydroxylamine to form an imine (Scheme 30) <1980JOC4198>. The reverse reaction, that is, conversion of thiocarbonyl to carbonyl, is possible with trifluoroacetic anhydride in dichloromethane <1991TL1195>. 

In all of these reactions, the diaryl tellurium oxide is reduced to the diaryl tellurium. To make the conversion of thiocarbonyl to carbonyl groups catalytic with respect to the diaryl tellurium oxide, the diaryl tellurium must be converted back to the diaryl tellurium oxide. A catalytic cycle was developed with 1,2-dibromotetrachloroethane as the agent oxidizing the diaryl tellurium to the diaryl tellurium dibromide and 20% aqueous potassium carbonate as the base hydrolyzing the tellurium dibromide to the tellurium oxide1. 

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. ... 

Although neither of the two carbonyl groups in 18 is immune to the action of Lawesson s reagent,11 it is possible to bring about the selective conversion of the more Lewis-basic lactam carbonyl to the corresponding thiocarbonyl. Thus, treatment of 18 with Lawesson s reagent results in the formation of thiolactam 19 in 85% overall yield from 13. 

Conventional conversion of amide, lactam, imide, and urea carbonyl groups into enaminones, enamino esters, or enamino nitriles requires prior activation of the carbonyl groups either by alkylation to imino ethers, followed by reaction with activated methylene groups, or by thiation, e.g. with P2S5, to thiocarbonyl groups followed by alkylation (and possibly also oxidation), and, again, subsequent reac-... 

The conversion of a carbonyl to a thiocarbonyl group, or thionation , is a common procedure for the synthesis of thioketones. Several methods that use P4Sio,49 51 Lawesson s reagent (L.R.),2 52 57 H2S,58 59 NaHS,60 or hex-amethyldisilathiane (HMDST)61,62 are described. L.R. and P4S10 have been used to sulfurate partially and entirely perfluorinated carbonyl compounds,63 which are then trapped as anthracene adducts in a one-pot reaction. H2S has... 

Treatment of Fischer-type carbene complexes with different oxidants can lead to the formation of carbonyl compounds [150,253]. Treatment with sulfur leads to the formation of complexed thiocarbonyl compounds [141]. Conversion of the carbene carbon atom into a methylene or acetal group can be achieved by treatment with reducing agents. Treatment of vinylcarbene complexes with diborane can also lead to demetallation and formation of diols [278]. The conversion of heteroatom-substituted carbene complexes to non-heteroatom-substituted carbene complexes... 

Conversion of the thiocarbonyl group into carbonyl has been reviewed. In general, hydrolytic methods catalysed by metal ions are recommended over oxidative methods, as the former are typically cleaner and more easily worked up. 

An attempted synthesis of biotin using thiocarbonyl ylide cycloaddition was carried out (131,133,134). The crucial step involves the formation of the tetrahydrothiophene ring by [3 + 2] cycloaddition of a properly substituted thiocarbonyl ylide with a maleic or fumaric acid derivative (Scheme 5.27). As precursors of the thiocarbonyl ylides, compounds 25a, 72, and 73 were used. Further conversion of cycloadducts 74 into biotin (75) required several additional steps including a Curtius rearrangement to replace the carboxylic groups at C(3) and C(4) by amino moieties. 

The need for a variety of organofluorine molecules has encountered difficulties with oxygenated substitutes such as carboxylic esters due to their poor nucleophilicity towards electrophilic fluorinating reagents. This has led several groups to explore the conversion of the thiocarbonyl group into the CF2 moiety. It was successful with thioamides [174], dithioesters [175-177] and thionoesters [178, 179], providing new routes to difluoro-sulfides, amines, ethers and alkenes. 

With the exception of a few examples of nucleophilic attack on the thiocarbonyl group, including a more recently published method using sodium hydroxide under phase transfer conditions,most conversions are carried out with oxidative reagents. Sodium peroxide, dimethyl sulfoxide with acid or iodine,selenium-derived reagents and bis(p-methoxyphenyl)telluroxide have been used. 

Phosphorus pentasulfide is a valuable reagent for conversion of carbonyl into thiocarbonyl groups for instance, amides are converted to thioamides, ketones to thioketones (see Chapter 8, p. 137), carboxylic acids to thioacids, and alcohols are converted to the corresponding phosphorodithioic acids (18) (Scheme 16). 

Thiocarbonyls CS is not stable above - 160 C in the free state, but a number of complexes are known, such as RhCl(CS)(PPh3) (Eq. 4.16) and Cp(CO)Ru( x -CS)2RuCp(CO), but so far no pure or homoleptic examples M(CS) . They are usually made from CS2 or by conversion of a CO to a CS group. Perhaps because of the lower tendency of the second row elements such as S to form double bonds, the M =C—S form analogous to 4.2 is more important for MCS than MCO the MC bond therefore tends to be short and CS is a better ir acceptor than CO. Perhaps for this reason, CO and not CS tends to be substituted in a mixed carbonyl-thiocarbonyl complex. 

Alkylation at Sulfur and Selenium. Thioamides can be converted to the corresponding thioimidates via alkylation with MeOTf, which is very useful for introducing different functional groups at the thiocarbonyl carbon. Direct conversion of a thioamide to the amidrazone by heating with hydrazine was not successful, but the thioimidate readily reacted with hydrazine at room temperature to afford the desired product (eq 18). It has been reported that thioiminium salts generated in situ from thioamides and MeOTf can be used to construct... 

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