1.2.5- Thiadiazole-3,4-dicarbonitrile

Diiminosuccinonitrile reacts with sulfur dichloride in dichloromethane at room temperature to give 1,2,5-thiadiazole-3,4-dicarbonitrile 226 in 93% yield <1972JOC4136>. The addition of catalytic naked chloride to the reaction mixture gave the bi-l,2,5-thiadiazole 227 <1991CB1517>. No experimental data were given for this transformation, but it was shown that the bi-l,2,5-thiadiazole 227 can be formed directly from dicyanothiadiazole 226 under analogous reaction conditions (Equation 53) <1991CB1517>. 

Treatment of (15) with nitrous acid gives liT-l,2,3-tria2ole-4,5-dicarbonitrile [53817-16-6J (70). The action of thionyl chloride on (15) gives l,2,5-thiadiazole-3,4-dicarbonitrile [23347-22-0] (71). 

A useful strategy for the formation of fused thiadiazoles is the annulation of suitably functionalized 1,2,5-thiadiazoles. Common routes involve the use of 3,4-difluoro-l,2,5-thiadiazole, 3,4-diamino-1,2,5-thiadiazole, l,2,5-thiadiazole-3,4-dicarbonyls, l,2,5-thiadiazole-3,4-dicarbonitrile, amino-1,2,5-thiadiazole-3-carboxamides and carboxamidines. These afford heteroarene-fused 1,2,5-thiadiazoles (which are covered in Volume 9). Below follows a brief description of fused thiadiazoles that fall within the scope of this chapter. 

Thiadiazoles are weak bases. They form salts with mineral acids and addition compounds with heavy-metal salts. Ethenebis(triphenylphosphane)platinum(0) reacts with 1,2,4-thiadiazole-3,5-dicarbonitrile (15) to give a chelate complex. Insertion of platinum takes place at the S—N bond to give the six-membered metalloheterocycle (16) (Equation (2)) <84AG(E)971>. 

Thiadiazoles. An acyclic NCCN system in which the NC links may be sp, sp2, or sp3 hybridized reacts with sulfur monochloride or sulfur dichloride to form the appropriate 1,2,5-thiadiazole <1968AHC(9)107, CHEC-111(5.09.9.1.5)545>. Aliphatic 1,2-diamines can be converted into 1,2,5-thiadiazoles using various sulfur sources such as tetrasulfur tetranitride, disulfur dichloride, sulfur dichloride, thionyl chloride, and V(V-ditosylsulfur diimide. Thus, l,2,5-thiadiazole-3,4-dicarbonitrile 555 is prepared from diaminomaleonitrile 554 using neat excess thionyl chloride (Scheme 250) <1995SR299>. 

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