X-RAY CRYSTALLOGRAPHIC ANALYSIS OF TAUTOMERIC DIHYDROPYRIMIDINE DERIVATIVES

Article abstract of DOI:10.1016/S0040-4020(01)88104-7

X-ray crystallographic analysis of various dihydropyrimidine tautomers was carried out. 4-(2-chlorophenyl)-5-ethoxycarbonyl-2,6-dimethyldihydro-pyrimidine 1 exists in an electron-localized 1,4-dihydro form with a flat boat conformation in the crystalline state. 6-Chloro-4-(2-chlorophenyl)-5-ethoxycarbonyl-2-methyldihydropyrimidine 2 synthesized as 1/2 HCl salt after extractive work-up under basic conditions consists of two different molecules with Cl atoms; the molecules of electron-localized 1,4-dihydro form 2a and electron-delocalized form 2b.Both forms are linked by hydrogen bonding around the center of symmetry in the unit cell.X-ray analysis of compound 2c prepared by the addition of excess HCl-Et2O to a solution of compound 2 exhibits an electron-delocalized structure of different molecular arrangement.