In the title compound, C(15)H(24)O(4), the six-membered ring shows a distorted chair conformation and the five-membered ring adopts an envelope conformation with the C atom bearing the methyl and OH groups as the flap. In the crystal, O-H⋯O hydrogen bonds link the mol-ecules into chains running along the a-axis direction.

In the title compound, C(17)H(19)NO(3), the isoxazolidine ring adopts an envelope conformation with the O atom as the flap. In the crystal, O-H⋯O hydrogen bonds form C(2) (3)(14) R(2) (2)(14) motifs.

In the title compound, C(14)H(16)BrNO(5), the isoxazolidine ring adopts an envelope conformation, with the N atom at the flap. In the crystal, inter-molecular C-H⋯N and C-H⋯O hydrogen bonds generate R(3) (3)(18) ring motifs which are fused into a ribbon-like structure extending along the b axis.

In the title compound, C14H13ClN2O5S, the chlorine-substituted tetrahydrofuran ring adopts a twist conformation and the other tetra-hydro-furan ring an envelope conformation with the O atom as the flap. The pyrrolidine ring adopts a twist conformation. In the crystal, C-H⋯O hydrogen bonds link the mol-ecules into zigzag chains running along the b-axis direction.

In the title compound, C(19)H(22)N(4)O(2), the tetra-hydro-pyrimidine ring adopts an envelope conformation (with the N atom connected to the benzyl group representing the flap). This benzyl group occupies a quasi-axial position. The two benzyl groups lie over the tetra-hydro-pyridimidine ring. The amino group is a hydrogen-bond donor to the nitro group.

In the title compound, C(14)H(11)Cl(2)N(3)S, the thia-zole ring is in an envelope conformation with the -CH(2)- group bonded to the S atom forming the flap. The crystal structure is stabilized by weak inter-molecular C-H⋯Cl and C-H⋯N hydrogen bonds.

In the title compound, C(19)H(18)O, the cyclo-hexene ring has an envelope conformation with the methine C atom on the flap. The phenyl and methyl-phenyl rings form a dihedral angle of 85.93 (11)°. The crystal packing is consolidated by van der Waals forces and weak C-H⋯π inter-actions.

In the title compound C(17)H(25)NO(2), the piperidin-2-one ring adopts an envelope conformation with the C atom in the 5-position as the flap. The crystal packing is stabilized by inter-molecular O-H⋯O hydrogen bonds, building a infinite chain along the b-axis direction. C-H⋯π inter-actions further stabilize the crystal packing.

In the title compound, C(12)H(10)O(4), the five-membered ring adopts an envelope conformation, with the Csp(3) atom at the flap [deviation = 0.145 (2) Å]. In the crystal structure, mol-ecules are linked by inter-molecular O-H⋯O and C-H⋯O hydrogen bonds, forming a three-dimensional network.

In the title pyrimidine derivative, C12H16N2OS, the tetra-hydro-pyrimidine ring adopts an envelope conformation with the C atom of the methyl-ene -CH2- group as the flap. In the crystal, N-H⋯O and N-H⋯S hydrogen bonds connect mol-ecules into undulating sheets perpendicular to the a axis.