The Mannich reaction in the synthesis of N,S-containing heterocycles 10. Recyclization of stable cyclic michael adducts, N-methylmorpholinium 6-R-6-hydroxy-1,4,5,6-tetrahydropyridine-2-thiolates, to pyrimido[4,3-b][1,3,5]thiadiazines under conditions of aminomethylation reaction

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5-Substituted N-methylmorpholinium 4-aryl-6-R-3-cyano-6-hydroxy-1,4,5,6-tetrahydro-pyridine-2-thiolates upon the action of primary amines and HCHO in ethanol undergo recyclization to 3,7-disubstituted 8-aryl-3,4,7,8-tetrahydro-2H,6H-pyrimido[4,3-b][1,3,5]thiadiazine-9-carbonitriles in low yields (5–28%). The latter were also obtained by alternative method, viz., by sequential condensation of cyanothioacetamide with aromatic aldehydes, primary amines, and HCHO.