Synthesis of polyazaheterocycles containing linearly bound 1,2,4-thiadiazole using enaminones

A reaction of N -substituted 5-amino-3-(2-oxopropyl)-1,2,4-thiadiazoles with dimethylformamide dimethyl acetal gave 3-(5-amino-1,2,4-thiadiazol-3-yl)-4-(dimethylamino)but-3en-2-ones, whose cyclization with hydrazine, guanidine, 1 H -pyrazol-5-amines and 6-aminopyrimidin-4(3 H )-ones led to 3-methyl-1 H -pyrazole, 4-methylpyrimidin-2-amine, 5-methyl3-arylpyrazolo[1,5- a ]pyrimidines, and 5-methyl-2-R-pyrido[2,3- d ]pyrimidin-4(3 H )-ones containing a 5-amino-1,2,4-thiadiazole fragment linearly bound at position 3.