1.3.5- Triazines reaction with active methylene compounds

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>. 

Aminomethylenation reactions of active methylene compounds with 1,3,5-triazine have also been described by Kreutzberger et al. <85AP(318)89, 85AP(3l8)82l>. A second equivalent of the active methylene compound can react as the third component to give ==CH—linked heterocycles, e.g. (61) from initial product (60) (Scheme 10) <86AP(319)18). 

Nucleophilic attack at the fully conjugated 1,3,5-triazine usually results in ring cleavage. Thus, active methylene compounds react with 1,3,5-triazine in aminomethylenation reactions. A three-component reaction of cyclopentadiene with 1,3,5-triazine and a secondary amine leads to /V,7V-di substituted pentafulven-6-amines (304) and N2-(6-pentafulvenyl)formamidines (305)... 

The addition of active methylene compounds of C-5 of 6-methyl-3-phe-nyl- 1,2,4-triazine demonstrates a wider applicability of the reactions with carbanionic reagents for the synthesis of 5-substituted triazines (Scheme 13) (87CPB1378). 

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