In the title fused-ring compound, C(12)H(13)NO(3), the two five-membered C(3)NO rings both approximate to envelope conformations with C atoms in the flap positions. The OH group of the pendant CH(2)OH unit is disordered over two positions in a 0.528 (5):0.472 (5) ratio. One of the OH groups participates in an O-H⋯N hydrogen bond, generating centrosymmetric dimers in the crystal structure.

The title compound, C17H20O2, has an E conformation about the bridging C=C bond. The cyclo-hexene ring adopts an envelope conformation with the dimethyl-substituted C atom as the flap. Its mean plane makes a dihedral angle of 7.20 (12)° with the benzene ring. In the crystal, neighbouring mol-ecules are connected via C-H⋯O hydrogen bonds, forming chains running along the a-axis direction.

In the title compound, C(38)H(34)Cl(2)N(4)O(2), the piperazine ring adopts a chair conformation. The pyrrolidine rings that are fused to the piperazine ring adopt envelope conformations (in which the C atoms connecting the two rings represent the flap). The indoline ring systems are approximately planar (r.m.s. deviations = 0.026 and 0.034 Å) and are aligned at a dihedral angle of 54.98 (3)°.

In the title compound, C(27)H(20)BrNO(3), the pyrrolidine ring adopts a half-chair conformation, while the other five-membered rings adopt flattened envelope conformations with the spiro C atoms as the flap atoms. An intra-molecular C-H⋯O hydrogen bond occurs, generating an S(6) ring. In the crystal, mol-ecules are connected via weak C-H⋯O hydrogen bonds, forming chains along the c axis.

The title spiro-compound, C(20)H(16)N(4)O, crystallizes with four independent mol-ecules in the asymmetric unit. In all of them, the oxindole unit is planar, the r.m.s. deviations ranging from 0.07 to 0.08 Å, while the pyrrolinyl ring adopts an envelope conformation (with the N atom representing the flap). In the crystal, adjacent mol-ecules are linked by N-H⋯N and N-H⋯O hydrogen bonds.

In the title compound, C(9)H(8)Br(2)O, the cyclo-pentene ring adopts an envelope conformation with the brominated C atom as the flap. In the crystal, mol-ecules are linked by strong O-H⋯O hydrogen bonds into zigzag C(4) chains along [010]. In addition, a C-H⋯π inter-action involving the benzene ring and the H atom attached to the hy-droxy-lated C atom is observed.

The racemic title compound, C11H12N2O3, contains a [4.3.0]bicyclic unit in which the shared C-C bond adopts a cis configuration. The five- and six-membered rings are in twisted envelope (with the bridgehead C atom bearing the methoxy substituent as the flap) and distorted chair conformations, respectively. In the crystal, the mol-ecules are linked via weak C-H⋯O iteractions, forming ladder-like...

In the title compound, C(17)H(17)N(3)O(2)S, the phenyl ring is oriented at dihedral angles of 8.5 (2) and 1.17 (14)°, respectively, to the C=N-N plane and the fused aromatic ring. The thia-zine ring adopts an envelope conformation with the S atom at the flap. In the crystal, a weak C-H⋯O inter-action connects the mol-ecules, forming a helical chain along the a axis.

X-ray crystallography firmly established the relative stereochemistry of the title compound, C16H20N2O3. The acetonide ring adopts an envelope conformation with one of the O atoms as the flap and the piperidine ring adopts a slightly twisted boat conformation. The absolute configuration was determined by use of d-ribose as the starting material. The compound exists as O-H⋯O hydrogen-bonded chai...

The six-membered cyclo-hexene ring in the title compound, C(26)H(38)ClNOS(2), adopts an envelope conformation, with the C atom bearing the two methyl groups representing the flap. This atom deviates by 0.642 (4) Å from the plane passing through the other five atoms of the ring (r.m.s. deviation = 0.053 Å). The mol-ecular conformation is stabilized by an intra-molecular N-H⋯S hydrogen bond.