X-ray diffraction studies of 6-methyl-5-acetyl-4-α -furyl-2-keto-1,2,3,6-tetrahydropyrimidine and 6-methyl-5-acetyl-4-γ -bromophenyl-2-thio- 1,2,3,6-tetrahydropyrimidine

6-Methyl-5-acetyl-4-α-furyl-2-keto-1,2,3,6-tetrahydropyrimidine (I) and 6-methyl-5-acetyl-4-γ-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. © 2003 MAIK "Nauka/Interperiodica".