In the title compound, C19H18ClNO3, the non-aromatic part of the fused ring system adopts an envelope conformation with the central methyl-ene C atom as the flap. The dihedral angle between the pyridine and benzene rings is 56.98 (3)°. In the crystal, mol-ecules are linked into double layers parallel to (100) by a network of weak C-H⋯O inter-actions.

In the title compound, C(9)H(14)O(3), the cyclo-hexenone ring has an envelope conformation; the flap atom (with the hydroxy-methyl groups attached) is displaced by 0.582 (4) Å from the plane of the other five ring atoms. The crystal structure contains an inter-molecular O-H⋯O hydrogen-bonded ring.

In the title compound, C(14)H(13)N(3)O(3), the pyrazoline ring assumes an envelope conformation with the furanyl-bearing C atom at the flap position. The dihedral angle between the furan and nitrobenzene rings is 84.40 (9)°. Weak inter-molecular C-H⋯O hydrogen bonding is present in the crystal structure.

The crystal structure of the title compound, C26H39BO2, which contains no strong hydrogen bond donors, displays only long C-H⋯O contacts between inversion-related pairs of mol-ecules. The structure contains layers rich in oxygen and boron parallel to the ac plane. The dioxaborinane ring adopts an envelope conformation with the C atom attached to the two methyl groups as the flap .

In the title mol-ecule, C(17)H(18)O(5), which was prepared by the reaction of (R)-1,5-dioxaspiro-[5.5]undecane-2,4-dione and 4-meth-oxy-benzaldehyde with ethanol, the 1,3-dioxane ring is in a distorted envelope conformation with the spiro C atom forming the flap. The crystal structure is stabilized by weak inter-molecular C-H⋯O hydrogen bonds.

In the title compound, C(26)H(22)N(2)O(3), the pyrrolidine ring adopts an envelope conformation with the N atom as the flap. In the crystal, pairs of centrosymmetrically related mol-ecules are linked into dimers by N-H⋯O hydrogen bonds. In addition, there are C-H⋯O hydrogen bonds.

The title compound, C16H24Cl2O, is built up from two fused six- and seven-membered rings which bear a di-chloro-cyclo-propane group and an ep-oxy group, respectively. In the mol-ecule, the six-membered ring adopts an envelope configuration with the C atom linking the ep-oxy ring at the flap, while the seven-membered ring adopts a boat-sofa conformation.

In the title compound, C20H15NOS, the dihedral angle between the phenyl rings is 74.25 (6)°. The six-membered 1,3-thia-zine ring has an envelope conformation with the C atom at the 2-position forming the flap. The crystal structure features weak C-H⋯O inter-actions, which lead to the formation of a tape motif along [110].

In the title compound, C(28)H(20)F(3)NO(3), the pyrrolidine ring adopts a half-chair conformation. The other five-membered rings adopt envelope conformations with the spiro and methylene C atoms as the flap atoms. In the crystal, mol-ecules are connected via weak C-H⋯O hydrogen bonds, forming sheets parallel to the bc plane.

In the title compound, C19H19NO3S, the thia-zole and oxazolidine rings each adopt an envelope conformation, with the S and O atoms as the respective flap atoms. The thia-zole and oxazolidine rings (all atoms) make a dihedral angle of 66.39 (11)° while the phenyl rings subtend a dihedral angle of 22.71 (10)°.