1,2,4-Thiadiazolines 4- alkyl-5-imino

The mass spectra of a series of 3-amino-4-aryl-5-aryl(or alkyl)imino-A2-1,2,4-thiadiazolines (366) have been interpreted in terms of fragmentation patterns, that are the result of fission of the molecules by routes a-c.257 (see also Ref. 49). In an extension of this study to variously substituted 3,5-... 

Alkyl-5-imino-3-methyl-A2-l,2,4-thiadiazolines react exothermally at 0°C with dibenzoyl or dimethoxy carbonylacetylenes in tetrahydrofuran to give the 2-aIkylaminothiazoles in high yields (1564). The cyclo addition reaction of 2-pyridyl isothiocyanates with 1-azirines results in the formation of 2-pyridylaminothiazoles (1565). 

Treatment of 2,5-diamino-l,3,4-thiadiazole with an a-haloketone in ethanol, followed by reaction of the resulting 2-imino-3-(a-keto-alkyl)-5-amino-l,3,4-thiadiazoline hydrohalide (33) with aqueous ammonia, and then excess of hydrazine hydrate, leads to 1 -amino-imidazole-2-thiones (34).144... 

Akerblom and Skagius - and Skagius have prepared 3-alkyl-l,3,4-thiadiazolin-2(3)-ones (95) from aminothiadiazoles (4) by ring-alkylation to 95, nitrosation of the imino group to 96, and thermal decomposition of the nitrosamine to 97. The reaction seems to be quite general, since it has been performed with R = amino, alkoxy, and 2-nitro-5-furyl. ... 

With activated acetylenes (27, X = PhCO, COOMe), Hector s bases yield substituted 2-arylaminothiazoles (29). The course of the reaction may be rationalized by assuming the usual intermediate heteropentalene formation (28).42 4-Alkyl-5-imino-3-methyl-A2-l,2,4-thiadiazolines (30) undergo the same type of reaction.43... 

Bond Switch at n-Hypervalent Sulphur.—Condensation of S amino-3-methyl-1,2,4-thiadiazole (190) with alkyl or aryl cyanides affords an equilibrium mixture of products (191) and (192). A similar bond switch is observed when the 5-imino-l,2,4-thiadiazoline (193) is treated with the imino-ester MeC(=NH)OEt, as... 

From dithiazoles. The alkylation of phenylthiuret (45) is attended by isomerization to 1,2,4-thiadiazole derivatives. Thus methylation or benzylation in alkaline media gives 5-imino-3-alkylthio-2-phenyl-l,2,4-thiadiazolines (46 R = Me or PhCHg, R = Ph, R = H), which can be independently synthesized by the oxidation of 2-5-alkyliso-l-phenyldithiobiuret (47 R = Me or PhCHg, R = Ph, R = H). Conversely, the dealkylation, by concentrated hydrochloric acid, of 3-t-butylthio-5-phenylimino-l,2,4-thiadiazoline (46 R = Bu R = H, R = Ph), obtained from (47 R = Bu , R = H, R = Ph), proceeds with the opposite isomerization, yielding (45) instead of the expected (46 R = R = H, R = Ph). Possible mechanisms of these reactions, and their significance for the structure of phenylthiuret, have been discussed. However, the issue is complicated by the fact that different alkyl halides produce different structural types of the 1,2,4-thiadiazole system. ... 

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