Isothiazoles from 1,2-dithiolium salts

Judging from these early results, it appears that the reaction of 1,2-dithiolium salts with ammonia offers an elegant synthesis of certain substituted isothiazoles that are difficult to obtain by other methods.98 The reaction of the unsubstituted 1,2-dithiolium salt with NH8, however, does not yield the parent isothiazole system. Moreover, in the case of the 3(5)-methyl salts, the abstraction of a methyl proton activated by the positive charge of the ring successfully competes with this reaction (Section II,B,4).14a... 

There are at present no detailed data available as to whether and to what extent the formation of isothiazoles from unsymmetrically monoaryl-substituted 1,2-dithiolium salts is stereoselective, or how the ratio of the isomera can be influenced by variation of the substitution. 

Further examples have been given of the reaction of 1,2-dithiolium salts (both 3,4-dialkyl and 3,5-dialkyl) with ammonia to give isothiazoles, and the formation of ring-opened products, (45) and (46), from 3-aryl-l,2-dithiolium perchlorates and excess of dimethylamine has been reported. The reactions of 3-methylthio-l,2-dithiolium salts with amines continue to be of interest. With primary aliphatic amines, 5-aryl-3-methylthio-l,2-dithiolium iodides give j8-alkylaminodithioacrylates (47) and isothiazoline-3-thiones (48) as well as the demethylated compounds (l,2-dithiole-3-thiones). Similar products are obtained with secondary amines, except that the isothiazole derivatives are replaced by 3-dialkylamino-l,2-dithio-lium iodides (49), the n.m.r. spectra of which indicate restricted rotation... 

From, 2-Dithiolans Type C). The general synthesis of isothiazoles from 1,2-dithiolans (see Vol. 2, p. 563 Vol. 3, p. 543) by reaction with ammonia or amines continues to be exploited. 3-Ethoxy-l,2-dithiolium salts (1) are cleaved by primary amines to the linear thioesters (2), which are in turn convertible into... 

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