Thiocarbonyls conversion reaction

After identification of various intermediate compounds, a proposed mechanism of this process was reported in 1996 (Scheme 12.2) [34,36]. It was found that by limiting the reaction time to 3 h, only a trace of PITN was produced and the majority of the reaction mixture was composed of unreacted phthaKc anhydride (30). However, the mixture was also found to contain a number of intermediates (Scheme 12.2, 32-35) that could be identified by mass spectrometry. Intermediates 32 and 34 were also independently synthesized and successfully reacted with P4S10 to produce PITN in both shorter periods of time and with higher yields than by the initial anhydride 30. The rate-determining step of the polymerization process was determined to be the initial conversion of carbonyl to thiocarbonyl through reaction of 30 with P4Sio. 

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... 

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>. 

Thiocarbonyl compounds undergo conversion into difluoromethylene compounds, generally under milder conditions than the corresponding carbonyl compounds. These reactions differ from those of sulfur tetrafluoride with carbonyl compounds in that a formal oxidation-reduc-... 

Makino et al.35 developed a solid-phase synthesis of 1,3-disubstituted 2-thioxoquinazoline-4-ones using HMP Lanterns that were derivatized with a 4-aminobenzoate ester. Following the assembly of amide 25 (Scheme 9), SnAt reaction with alkyl amines gave support-bound products 26 with high conversion. The key thiocarbonylation step was achieved with thiocarbo-nyldiimidazole in decalin at 95° for 16 h in the presence of DMAP to afford 1,3-disubstituted 2-thioxoquinazoline-4-ones 27. The target compounds 28... 

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. 

Huisgen and co-workers reported, in three papers (02T507, 02T4185 and 02HCA1523> the conversion of various 1,3,4-thiadiazolines 86 into thiocarbonyl ylides 87 via extrusion of N2. They then described cycloaddition reactions of these ylides 87 with various a,P-unsaturated esters and nitriles and postulated reaction mechanisms for the regioselectivity and stereochemistries observed in the transformations. 

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. 

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. 

Another example of conversion of a carbonyl into a thiocarbonyl is provided by dibenzodiazocinone 32 which, upon reaction with Lawesson s reagent, furnished the dithiocarbonyldiazocine 33 in 91% yield <2004JOC1248>. 

A number of conversions of thiocarbonyl compounds into gem-difluoro compounds have been described in the literature, e.g. formation of 1.189 2,212 3,213-214 4,216 5,212 6,213 7 (Houben-Weyl. Vol.E4, p668),217 and 8.218 Since these reactions give difluoro compounds bearing heteroatoms in the a-position they are not discussed further here. Pyrolysis of 4 gives 1,1-difluoro-substituted alkenes in good yields.216... 

A number of reactions of organothiols with complexes of alkoxycar-benes, isocyanides, or thiocarbonyls, leading to thiocarbene complexes, have been reviewed (4,125,126). Further related examples include the conversion of a chlorocarbene to a dithiocarbene by reaction of the ruthenium complex 154 with RSH (R = Me, p-tolyl) or HSCH2CH2SH to give the dithiocarbene compounds 155 and 156 (82). 

The use of benzeneseleninic anhydride in the conversion of thiocarbonyl compounds into the corresponding oxo-derivatives has been reported in full similar reactions were achieved using diaryl telluroxides. ° Steroidal ketones reacted with tris(phenylseleno)borane or tris(methylseleno)borane to give phenyl or methyl selenoacetals. 

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