In the title compound, C(11)H(11)N(3)O(4), the 3,5-dioxopiperazine ring adopts an envelope conformation, with the N atom connecting to the -CH(2)COOH group on the flap. In the crystal, mol-ecules are linked by O-H⋯N hydrogen bonds to produce a linear chain running along the c axis. π-π stacking is observed between parallel pyridine rings of adjacent mol-ecules, the centroid-centroid distance be...

In the title compound, C19H19BrO2, the cyclo-hexenone ring adopts an envelope conformation with the C atom bearing the methyl substituents as the flap. In the crystal, weak π-π stacking is observed between parallel aromatic rings of adjacent mol-ecules, the centroid-centroid distance being 3.694 (6) Å. The entire bromonaphthylmethyl unit is disordered over two orientations, with a site-occupanc...

In the title compound, C21H20N2O3, the lactone ring adopts an envelope conformation with the quaternary C atom bonded to two other C atoms as the flap. The fused pyrrolidine ring adopts a twisted conformation about the Cq-N (q = quaternary) bond. In the crystal, inversion dimers linked by pairs of N-H⋯O hydrogen bonds generate R 2 (2)(8) loops. The dimers are linked into [110] chains by pairs o...

In the title compound, C25H36N2O2, the two tert-butyl-substituted benzene rings are inclined at an angle of 53.5 (3)° to one another. The imidazolidine ring has an envelope conformation with with one of the C atoms of the ethylene fragment as the flap. The structure displays two intra-molecular O-H⋯N hydrogen bonds that generate S(6) ring motifs. The crystal studied was a non-merohedral twin wi...

In the title compound, C(14)H(13)ClN(2)O, the fused hydro-pyrimidine ring adopts an envelope conformation with one of the methyl-ene C atoms at the flap. The three-membered ring is approximately perpendicular to the attached isoquinoline ring system, with a dihedral angle of 89.44 (11)°. In the crystal, mol-ecules are linked by a weak C-H⋯π inter-action, forming a helical chain along the c axis.

In the title compound, C(23)H(31)NO(2), the lone pair on the nitro-gen atom is oriented to facilitate intra-molecular hydrogen bonding with the hydr-oxy group residing on the phenyl substituent. The five-membered ring adopts an envelope confornmation with the O atom at the flap. The absolute stereochemistry was verified by measurement of optical activity using a digital polarimeter.

In the title compound, C(11)H(15)N(3) (2+)·2NO(3) (-), one of the imidazole N atoms and the N atom of the pyrrolidine ring are protonated. The pyrrolidine ring adopts an envelope conformation, with the C atom carrying the benzoimidazolium substituent as the flap atom. In the crystal structure, cations and anions are linked through N-H⋯O hydrogen bonds, forming chains that run parallel to the c ...

In the title compound, C20H21NO2, the pyrrolidine ring adopts an envelope conformation with the N atom at the flap position. The central benzene ring makes dihedral angles of 21.39 (10) and 80.10 (15)° with the phenyl ring and the mean plane of the pyrrolidine ring, respectively. The mol-ecular conformation is stabilized by an intra-molecular O-H⋯N hydrogen bond, which closes an S(6) ring. A we...

The title compound, C(10)H(7)FO(4), is an inter-mediate in the synthesis of the drug Fidarestat, (2S,4S)-2-aminoformyl-6-fluoro-spiro[chroman-4,4'-imidazolidine]-2',5'-dione. The di-hydro-pyran-one ring adopts an envelope conformation with the asymmetric C atom in the flap position. In the crystal, the mol-ecules are linked into zigzag chains along [100] by O-H⋯O hydrogen bonds and C-H⋯π inter-...

In the title mol-ecule, C(11)H(11)Cl(2)NO(2), the oxazolidine ring is in an envelope conformation with the O atom forming the flap; the other four essentially planar ring atoms (r.m.s. deviation = 0.012 Å) form a dihedral angle of 91.1 (3)° with the phenyl ring. In the crystal structure, mol-ecules are linked by weak inter-molecular C-H⋯O hydrogen bonds, forming one-dimensional chains.