ON THE STRUCTURE OF SOME SUBSTITUTED 4,6-PYRIMIDINEDIONES

5-Substituted hiocarbamoylimino)-4,6(1H,3H,5H)-pyri-midinediones (1) w ere transformed by oxidation into the new oxygen analogs (2) or to 5-s ubstituted do)-1-methyltetrahydro-4,6(1H,5H)-pyrimidinediones (3). Spe ctral data (H-1, C-13 NMR, IR) indicated an imino-type structure for 1 and 2, stabilized by an intramolecular hydrogen bond ([Pyridine]N-3-H ....X=C-2, [Thiourea], X=S,O) and solvent dependent E,Z isomerism of t he nonbonded terminal MeNHC=X group. In contrary, the structurally fix ed isoureido-pyrimidine system of 3 exists in one form and its structu re is stabilized by another intramolecular hydrogen bond - ([Pyrimidin e]N-3...HN3,Me[Isourea]).