Oxidation of l,2-dithiole-3-thiones

The anodic oxidation of l,2-dithiole-3-thiones (R R = H, Ph, respectively) was reported [9,10] to yield disulfide-linked bis(dithiole-3-thione) dication (Scheme 3). 

Other types of oxidation by electron loss are related to the formation of a disulfide linkage between two molecules of dithiole compounds. For instance, dications are formed by anodic oxidation of l,2-dithiole-3-thiones, and of l,6,6aA -trithiapentalenes, which may be considered as vinylogs of l,2-dithiole-3-thiones (Scheme 7). 

Sulfines 80 were obtained from the thermolysis of lithium salts of tosylhy-drazones of l,2-dithiol-3-ones (79) in the presence of oxygen.134 A series of these S-oxides was obtained by oxidation of l,2-dithiole-3-thiones with one equivalent of peracid under conditions where the S-oxide precipitates. Further addition of peracid gave the 1,2-dithiolylium salt (811.134 The sulfines can be prepared from m-chloroperbenzoic acid in 30-70% yields and with sodium periodate as an oxidant.135 Oxidation with reactive reagents such as (Ph0)3P03, 03, NaOCl, benzoyl peroxide, and HgO gave l,2-dithiol-3-one via the sulfine.135... 

A limited number of dithioles with carboxy and other substituents are known, but an oxidation of l,2-dithiole-3-thione-5-carboxylic acid with peracetic acid caused decarboxylation <60C1(L)1568>, suggesting that 3- or 5-carboxy-1,2-dithiolium cations decarboxylate readily. 

Examples of reactions involving replacement and cyclization are the long-known preparation of thiophenes (89) from 1,4-diketones, and the formation of l,2-dithiole-3-thione (90) from the salicylate ester analog (91).120 In the latter instance, oxidative cyclization with formation of an S—S bond has occurred this is a common feature of these reactions, particularly if such a link is needed to complete a five-membered ring. Another example of this aspect is afforded by the reaction of the propane-1,3-dione derivatives (92) which yield 3,5-diaryl-1,2-dithiolylium salts (93) when heated with phosphorus pentasulfide in carbon disulfide, followed by perchloric acid.121... 

Ethylation of l,2-dithiole-3-thione gives a 3-ethylthio-l,2-dithiolylium ion whose electroreductive dimerization has been investigated. A series of aryl-substituted l,2-dithiol-3-ylidene acetophenones underwent oxidative dimerization via cation-radicals (142) when electrolyzed the dimeric products, which contain a new C—C bond, were elaborated chemically into a series of highly conjugated derivatives including bithiathiophthenes. " ... 

Reactions.—Several interesting new developments in the chemistry of l,2-dithiole-3-thiones have been reported. 5-Aryl derivatives are converted, by anodic oxidation in acetonitrile, into dimeric dications, for example (10), which can be isolated as the insoluble perchlorate. With keten in benzene solution, the 5-aryl compounds give unstable green products which are formulated as thiolactones (11) treatment of these with acid... 

In a study of the oxidation of various heterocyclic thiones with peroxyacetic acid, l,2-dithiole-3-thiones (10) carrying electron-withdrawing substituents have been found to give l,2-dithiole-3-ones rather than dithiolium salts. Experimental details have been published for addition reactions of l,2-dithiole-3-thiones with acetylenes, and with benzyne. Reactions with enamines, leading to thiopyran derivatives (11), have been described. ... 

The synthesis, X-ray structure and solid state NMR of 4,4-dimethyl-l,2-ditellurolane 75 have been reported <98PS(136-8)291>. Chemoselective oxidation of 1,2-dithiole derivatives using dimethyldioxirane to give products such as 76 has been described <00SUL169>. Cycloaddition of dihydroquinoline-fused l,2-dithiole-3-thiones 77 with DMAD gives the spiro 1,3-dithioles 78 <99CHE587>. Dicationic thiatelluroles such as 79 have been prepared <00AG(E)1318>, anti cancer properties have been claimed for the simple dithiolopyrrolones... 

Oxo dithioic acids react with a combination of (Me3Si)2S and A-chlorosuccinimide in the presence of imidazole to give oxidative ring closure to the 3//-l,2-dithiole-3-thiones (equation 21)39. 

Peracetic acid or hydrogen peroxide are generally used in this preparation. If the l,2-dithiole-3-thione has bulky aliphatic substituents, nitric acid at 60-80°C may also be used as oxidizing agent, as in the preparation of 3-/er/-butyl-4-neopentyl-l, 2-dithiolium cation, which can also be obtained using hydrogen peroxide. ... 

Polarographic studies of the reduction of the parent l,2-dithiole-3-thione (27) show two waves.169 The first one corresponds to a two-electron reduction of the thiocarbonyl group to a thiol followed by an oxidation to disulfide 121. The second wave is a catalytic hydrogen wave. The reduction could not be carried out on a preparative scale owing to reactions with the mercury electrode. 

The anodic oxidation of a series of substituted l,2-dithiole-3-thiones has been studied and S—S linked dications 124 were isolated. Oxidation and... 

Tetracyanoethylene oxide reacts with l,2-dithiole-3-thiones with formation of l,2-dithiol-3-ylidene malonitriles 162 these could also be obtained from tetracyanoethylene.233... 

H-l,2-Dithiole-3-thiones The treatment of )3-oxodithioic acids with H2S and bromine leads to the heterocyclic compounds. Bromine serves as an agent for the oxidative cyclization. 

Dithioles. Diselenoles. and Dltelluroles.- Treatment of ethyl benzoylacetate with Lawesson s reagent (188) gives the l,2-dithiole-3-thione (189) 197 the latter reacts with arenediazonium fluoroborates to yield the 1,2-dithioliua salts (190 R = aryl). The action of -methylbenzylidenemalononitrile, PhMeC C(CN)2, on the methylthio-analogue (190 R = Me) leads to a mixture of the condensation product (191) and the thieno[3,2-b]thiopyranimine (192).199 The mesoionic dithiolium oxide (193) has been prepared from -dichloroacetone and sulphur, followed by methylation. 

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