1.2- Dithiolium salts pyrazoles

Rather surprisingly, the product of the reaction between the 3,4-diphenyl-l,2-dithiolium salt and ammonia in ethanol was found to contain 4,5-diphenyltrithione, but no isothiazole, although the reaction with phenylhydrazine gave a 95% yield of the corresponding pyrazole.46... 

This pyrazole synthesis, which undoubtedly profits from the thermodynamic stability of the end products, gives excellent yields (Table VI). Its range of application is limited, however, by the fact that the reaction of 3-substituted unsymmetrical dithiolium salts with substituted hydrazones leads to mixtures of isomers which can be separated only with difficulty. On the other hand, it does permit the preparation of a single 4,5-disubstituted pyrazole from a 3,4-disub-stituted salt and a substituted hydrazine. 

Dithiolium salts react with hydrazines similarly to amines, but further cyclization gives pyrazoles (46) or pyrazolium salts (47). When there are replaceable substituents, hydrazones and azines are formed. A mesoionic l,2-dithiole-3-olate (20 R = Ph) reacts similarly at C(3) with aniline, but with eventual formation of the products (48) and (49) <87CJC2830,92T8127). The reaction... 

The formation of pyrazoles from 3-aryl- or 3,5-diaryl-l,2-dithiolium salts and phenylhydrazine has been investigated in some detail. 3-Chloro-... 

Ring-opening reactions of dithiolium salts with amines continue to receive attention. The behaviour of 3-styryl derivatives deuteriated in various positions/ and of 3-ethoxy-1,2-dithiolium salts/ has been studied. Further examples have been provided of the formation of isothiazoles and pyrazoles by the action of ammonia and hydrazine, respectively. 3,5-Di-isopropyl-l,2-dithiolium cations are deprotonated by aqueous ethanolic ammonia to give the dithiole (29). ... 

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