1.3.4- Thiadiazolium salts, 2-methylthio

Methylthio-1,3,4-thiadiazolium salts (297) were treated with hydrazines in the ratio 1 2 to afford l,4-dihydro-l,2,4,5-tetrazine-6(5//)-thiones (298). In most cases the acyclic intermediate could not be isolated (73CZ565,73CZ566,01CB2311). 

Espinosa, A., A. Frontera, R. Garcia, M.A. Soler, and A. Tarraga. 2005. Electrophilic behaviour of 3-methyl-2-methylthio-l,3,4-thiadiazolium salts A multimodal theoretical approach. Arkivoc 9 415 37. 

The A -arylidene derivatives (96) of 4-amino-4,5-dihydro-l-methyl-3-methylthio-l/f-[l,2,4]tri-azole-5-thione, when treated with phosphorus pentachloride, are cyclized to give the 3-methylthio[l,2,4]triazolo[3,4-6][l,3,4]thiadiazolium chlorides (97). This conversion is envisaged to involve the initial formation of an iminium salt (98) which by attack of the chloride ion gives the intermediate imidoyl chloride (99) subsequent cyclization by intramolecular nucleophilic attack of the thiocarbonyl sulfur atom turns it into the fused bicyclic product (97) (Scheme 7) <86LA1540>. 

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