In the title compound, C(38)H(37)NO(3), the pyran ring has an envelope conformation with the quaternary C(q) atom as the flap atom. The dihedral angle formed between the meth-oxy-phenyl group and the naphthalene ring system is 67.32 (6)°. The ethyl-amino groups lie to the same side of the plane through the phenyl ring and form dihedral angles of 84.6 (3) and 75.8 (2)° with it.

In the title compound, C(28)H(27)NO(5)S, the five-membered pyrrolidine ring, which exhibits an envelope conformation (the C atom at the spiral junction being the flap atom), makes dihedral angles of 57.37 (10) and 86.84 (8)°, respectively, with the phenyl ring and the acenaphthyl-ene ring system. In the crystal, mol-ecules associate via two C-H⋯O hydrogen bonds, forming R(2) (2)(20) and R(2) (2...

The mol-ecule of the title compound, C(26)H(34)O(8), a prednisolone derivative, contains three six-membered rings (A, B and C) and one five-membered ring (D). Ring A is planar and rings B and C adopt chair conformations, while ring D adopts an envelope conformation with the C atom bonded to the methyl group at the flap. The crystal structure is stabilized by intermolecular O-H⋯O hydrogen bonds.

In the title compound, C(17)H(16)ClN(3)O(2)S, the dihedral angle between the benzene rings is 7.75 (13)°. The thia-zine ring adopts an envelope conformation with the S atom as the flap at a distance of 0.813 (2) Å from the plane through the other five atoms. In the crystal, C-H⋯O hydrogen bonds link the mol-ecules into chains propagating in [100].

In the title compound, C(16)H(15)F(3)N(2)O(4), the relative stereochemistry of the four stereogenic C atoms has been determined. The carb-oxy-methyl and 2-(trifluoro-meth-yl)-phenyl substituents of the pyrrolidine cycle have a cis mutual arrangement. The five-membered saturated aza-cycle adopts an envelope conformation with the N atom occupying the flap position. In the crystal, adjacent mol-ec...

In the title compound, C(17)H(20)O(3), the five-membered cyclo-pentyl ring displays an envelope conformation, with the atom at the flap position 0.538 (3) Å out of the mean plane formed by the other four atoms. The dihedral angle between the benzene and furan rings is 63.34 (15)°. In the crystal structure, mol-ecules are linked through inter-molecular O-H⋯O hydrogen bonds, forming a zigzag chai...

In the title compound, C(29)H(26)N(2)O(3)S, the central imidazolidine ring adopts an envelope conformation with the N atom bearing the benzyl ring at the flap. The S atom has distorted tetra-hedral geometry. The benzyl and tosyl rings are oriented at a dihedral angle of 52.1 (1)°. The phenyl rings connected to the imidazolidine ring form a dihedral angle of 28.7 (1)°.

The five-membered ring in the title compound, C(6)H(13)O(3)P, exists in an envelope conformation with one of the ring C atoms at the flap position. The coordination geometry around the P atom is a distorted tetra-hedron. The crystal structure is stabilized by several weak C-H⋯O and P-H⋯O hydrogen bonds, forming a three-dimensional network.

The title compound, C(31)H(44)O(5), was synthesized from isostev-iol (systematic name: ent-16-ketobeyeran-19-oic acid). In the mol-ecule, the three six-membered rings adopt chair conformations and the stereochemistry of the A/B and B/C ring junctions are trans. The five-membered ring D adopts an envelope conformation with the methyl-ene C atom as the flap.

The six-membered ring of the title compound, C(8)H(11)NO(3), adopts an envelope shape with the C atom in the meta position of the carbonyl representing the flap. This atom is disordered over two positions in an 0.865 (6): 0.135 (6) ratio. In the crystal, a two-dimensional supra-molecular network parallel to the ac plane is built up from O-H⋯O and N-H⋯O hydrogen bonds.