Abstract A multi-component double Mannich cyclocondensation of 6-polyfluoroalkyl-2- thiouracils with formalin and heterocyclic amines (2-aminopyridine, 2-aminopyrimidine, 4- aminoantipyrine) proceeded regiospecifically at the C= S and NH centers giving rise to 3- hetaryl-8-polyfluoroalkylpyrimido [2, 1-b][1, 3, 5] thiadiazines. The regioisomeric structure of the products was established by X-ray crystallography, IR and NMR spectroscopy, GLC- ...