X-Ray Diffraction Studies Of 6-Methyl-5-Acetyl-4-Alpha-Furyl-2-Keto-1,2,3,6-Tetrahydropyrimidine And 6-Methyl-5-Acetyl-4-Gamma-Bromophenyl-2-Thio-1,2,3,6-Tetrahydropyrimidin E

6-Methyl-5-acetyl-4-alpha-furyl-2-keto-1,2,3,6-tetrahydropyrimidine (I) and 6-methyl-5-acetyl-4-gamma-bromophenyl-2-thio-1,2,3,6-tetrahydropyrimidine (II) are prepared by the modified Biginelli reaction, and their crystal and molecular structures are studied. It is shown that, in crystals I and II, the pyrimidine ring has an amide tautomeric form and adopts a sofa conformation. The IR absorption spectra are analyzed, and the stability of the tautomers of the pyrimidine fragments is evaluated using quantum-chemical calculations. (C) 2003 MAIK "Nauka/Interperiodica".