1.2.4- Triazine reaction with cyanide ions

The first example is the reaction of 5-unsubstituted 1,2,4-triazines (121) with cyanide ions, which affords bi-l,2,4-triazin-5,5 -yls (137) and l,2,4-triazine-5-carboxamides (138) <84CHEC-I(3)369, 87CPB1378). Bi-l,2,4-triazin-5-yls (137) were also isolated when (121) was treated with sodium methoxide or potassium in hquid ammonia. (Scheme 24) It is suggested that the methoxide-induced dehydro-dimerization proceeds via an anionic intermediate (139), while the reaction with potassium in liquid ammonia occurs by a free radical process. 

Reaction of 2,3-dichlorobenzoyl chloride with cyanide ion leads to the corresponding benzoyl cyanide (141). Condensation of that reactive intermediate with aminoguanidine 142 leads to the hydrazone-like product 143. Treatment with base results in addition of one of the guanidine amino groups to the nitrile function and formation of the 1,2,4-triazine ring. The product, lamo-trigine (144), is described as an anticonvulsant agent [31]. 

Thermolysis of the thiadiazole (164) leads to elimination of isocyanate and sulfur giving the triazine derivative (167). If the thermolysis is carried out in the presence of phenols 2-aryl-benzimidazoles (168) are produced <85JCS(P1)1007>. The S—N bond of (157) is readily cleaved with both N- and C-nucleophiles. Thus, treatment of (157) with an excess of amine gives the sulfenamide (169) (Scheme 39) and reaction of (157) with active methylene compounds leads to derivatives of type (170) (Scheme 39) which on heating furnish (171). Cyanide ion inserts into the S—N bond of (164), probably via the intermediate (172) which immediately recyclizes to give the thiadiazinone (173) (Scheme 40) <85JCS(P1)1007>. 

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