Structures of 1,2,3,4-tetrahydro-6H-pyrimido[2,1-b]-quinazolin-6-one and its hydrochloride

C₁₁H₁₁N₃O, m.p. 243°C, P2/n,Z=4,a=5.843(2),b=14.241(3),c=11.102(1) Å, =93.30(2)°,R=0.046; C₁₁H₁₁N₃O·HCl·H₂O, Pca2₁,Z=8,a=18.640(2),b=8.894(2),c=14.404(2)Å,R=0.062. The molecules of the free base are in 1H-tautomeric form. N(1)-H...N(11) hydrogen bonds join molecules of the free base into dimers, which enable tautomeric rearrangement (not observed in this study) also in the solid state without any changes in molecular packing. The quinazoline system deviates slightly from planarity and benzene electrons are partially localized at C(7)–C(8) and C(9)–C(10) bonds as seen from their lengths of about 1.375 Å, while other bonds in the benzene ring are at least 0.02 Å longer.