1.2- Dithiole-3-ones, ring opening

Grignard reagents commonly react at S(2) of l,2-dithiole-3-ones with ring opening (Scheme 18) (73LA247, 74LA1261, 82AHC(31)63>. 

There are no reports of aromatic substitution reactions on benzo- or dibenzotetrathiafulvalenes. With regard to the reactivity of the substituents on the benzene ring(s), the main examples involve 1,3-dithiol-2-ones and l,3-dithiole-2-thiones. The former afford octakis(alkylthio)dibenzote-trathiafulvalenes 25 through basic ring opening and subsequent alkylation... 

EWG-Activated 2-methylene dithioles (= cyclic ketene dithioacetals with electron-withdrawing substituents) 38 undergo a ring-opening reaction mediated by primary aliphatic amines to give polyfunctionalized 2-(alkylamino) thiophenes (40) after hydrolysis in a one-pot procedure [82] ... 

The products obtained by the action of bases and of Grignard reagents on 4,5-dichloro-l,2-dithiole-3-one include the 1,2,4-trithiolan (8), and 1,3-dithioles (9 R = COaMe or COSR). l,2-Dithiole-3-one is reported to give ring-opened trisulphides, e.g. RSSSCH=CHCOCl, with sulphenyl chlorides. Reactions of l,2-dithiole-3-ones with diphenyldiazomethane have also been investigated. ... 

Ring-opening reactions occur when l,2-dithiole-3-ones and -3-thiones are treated with sodium sulphide after methylation, products of type (5 X = O... 

Chloro-l,2-dithiol-3-ones (e.g., 71a) and 4,5-dichloro-l,2-dithiol-3-one (71b) react with Grignard reagents on sulfur with subsequent ring closure of the open-chain intermediates.12lb The dithiethanes were isolated in 57-97% yields. Both cis and trans isomers were formed. Dichloro compound 71b gives via thioketene derivatives l,3-dithiol-2-ylidene compounds in 12-75% yield. Mixtures of stereoisomers were obtained12 lb (Scheme 8). 

The reduction of l,2-dithiole-3-thiones (7) by means of triethylsilane probably involves an addition of the silane to the thiocarbonyl group with subsequent opening of the ring and reaction with one further mole of triethylsilane123 (Eq. 4). 

The preparative reduction, polarography, and cyclic voltammetry of 5-methyl-l,2-dithiole-3-thione have been studied.171 The results obtained are in agreement with a one-electron reduction of the thiocarbonyl group to a radical-anion, which could not be detected by ESR spectroscopy as it dimerizes too fast. The dimer is further reduced by a one-electron reduction to an anion in which the ring has been opened. (Scheme 12). The dianion could be isolated after methylation and was found to be identical with the compounds isolated by Maignan and Vialle by reduction with sodium sulfide.124 The dianion corresponds to the thioketonate dianion obtained by electrochemical reduction of 1,2-dithiolylium salts.172... 

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