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In the title compound, C23H34O4, the C/D and D/E rings are trans fused and the A/B ring possesses an anti fusion. The two cyclo­hexane rings adopt a chair conformation while the cyclo­hexene ring exhibits a half-chair conformation. The cyclo­pentane ring displays an envelope conformation with the C atom bearing the methyl group as the flap. In the crystal, the mol­ecules are linked by O—H⋯O hydrogen bonds, forming chains along the b axis.

The title dammarane triterpenoid, C30H50O4, assigned the name chrysura, was isolated from an ethyl acetate extract of Walsura chrysogyne leaves (Meliaceae). It has 20S*,24S* relative stereochemistry and an oxepanone ring with two methyl groups at position 4. The two cyclo­hexane rings adopt chair conformations. The cyclo­pentane and tetra­hydro­furan rings have envelope conformations; their mean planes make a dihedral angle of 13.1 (3)°, indicating that the rings are only slightly tilted with respect to each other. There is an intra­molecular C—H⋯O hydrogen bond in the mol­ecule, which forms S(6) and S(7) ring motifs. In the crystal, mol­ecules are linked via O—H⋯O and C—H⋯O hydrogen bonds, forming chains propagating along [001] which stack along the b-axis direction.

The asymmetric unit of the title compound, C32H51N3O3, consists of two crystallographically independent mol­ecules, A and B; the 2-methyl­pentane group of mol­ecule A and the propane group of mol­ecule B are each disordered over two sets of sites, with refined site-occupancies of 0.825 (5):0.175 (5) and 0.630 (18):0.370 (18), respectively. In both mol­ecules, the three cyclo­hexane rings in the steroid fused ring systems adopt chair conformations while the cyclo­pentane rings adopt envelope and twist conformations in mol­ecules A and B, respectively. In the crystal, N—H⋯O and C—H⋯O hydrogen bonds link the two independent mol­ecules together, generating R 2 1(7) and R 2 2(8) ring motifs.

The asymmetric unit of the title compound, C30H48ClN3O, contains two mol­ecules, A and B. In both mol­ecules, the three cyclo­hexane rings in the steroid fused ring systems adopt chair conformations, while the cyclo­pentane rings adopt envelope and twist conformations in mol­ecules A and B, respectively. In mol­ecule B, the cyano group is disordered over two orientations with refined site-occupancies of 0.593 (8) and 0.407 (8). An intra­molecular C—H⋯N inter­action forms an S(10) ring in both mol­ecules. In the crystal, mol­ecules are linked by N—H⋯O, C—H⋯O and C—H⋯N inter­actions, resulting is chains propagating along the a-axis direction.

In the deca­hydro­phenanthrenone ring system of the title compound, C27H44O, the two cyclo­hexane rings adopt chair conformations, whereas the cyclo­hexene ring adopts an envelope conformation. The cyclo­pentane ring is twisted. In the crystal structure, mol­ecules are stacked along the a axis, but no significant inter­molecular inter­actions are observed.

The title compound, C28H44O4·0.56H2O, is a co-crystal of methyl isoeichlerialactone monohydrate as the major component and methyl isoeichlerialactone as the minor component in a 0.55778 (3):0.44222 (3) ratio. The conformations of both components are identical except for that of the –COOCH3 group of the methyl propanoate side chain on the cyclo­hexane ring which is positionally disordered over two orientations. The mol­ecule of methyl isoeichlerialactone has three fused rings and all rings are trans-fused. The two cyclo­hexane rings are in standard chair conformations and the cyclo­pentane ring adopts an envelope conformation. In the crystal, weak C—H⋯O inter­actions link methyl isoeichlerialactone mol­ecules into screw chains along [010]. The crystal structure is further stabilized by O—H⋯O hydrogen bonds and weak C—H⋯O inter­actions.

The title compound, C30H50O5, was isolated from the bark of Aglaia smithii. There are two independent mol­ecules in the asymmetric unit that differ in the orientation of the isopropenyl group attached to the cyclo­hexane ring. The cyclo­hexane rings in both mol­ecules adopt chair conformations, whereas the cyclo­pentane and tetra­hydro­furan rings adopt envelope conformations. The independent mol­ecules are linked into a layer parallel to (010) by O—H⋯O hydrogen bonds.

The asymmetric unit of the title compound, C27H45ClO, consists of two crystallographically independent mol­ecules. In both mol­ecules, the three cyclo­hexane rings in the steroid fused-ring systems adopt chair conformations, while the cyclo­pentane ring adopts a half-chair conformation in one mol­ecule and an envelope conformation in the other. In the crystal, the mol­ecules are linked into a two-dimensional network by weak C—H⋯O hydrogen bonds. The crystal studied is a nonmerohedral twin with a refined ratio of twin components of 0.264 (3):0.736 (3).

In the title compound, C30H26N2O3, the two pyrrolidine rings adopt twisted and envelope conformations, whereas the cyclo­pentane ring adopts an envelope conformation. The least-squares planes through the pyrrolidine rings form a dihedral angle of 41.72 (10)°. The mol­ecular structure is stabilized by an intra­molecular O—H⋯N hydrogen bond, which generates an S(5) ring motif. Centrosymmetrically related mol­ecules are linked via two pairs of inter­molecular C—H⋯O inter­actions, forming R 2 2(16) ring motifs. In the crystal packing, the mol­ecules are linked into two-dimensional networks parallel to the ab plane via C—H⋯O inter­actions.

In the title mol­ecule, C34H53BrO4, all the cyclo­hexane rings adopt chair conformations, while the cyclo­pentane ring adopts an envelope conformation. In the crystal, weak inter­molecular C—H⋯O hydrogen bonds link the mol­ecules into corrugated sheets parallel to the ab plane.

In each of the two independent indene-4-spiro­pentane mol­ecules in the asymmetric unit of the title 2:1 adduct, C19H18N6·0.5C5H4OS, the cyclo­hexene ring adopts a half-chair conformation and the cyclo­pentene and cyclo­pentane rings adopt envelope conformations. The mean plane through the cyclo­hexene/cyclo­pentene fused system is aligned at a dihedral angle of 77.9 (1)° with respect to the mean plane through the cyclo­pentane ring in one mol­ecule and 87.0 (1)° in the other. In the crystal, adjacent indene-4-spiro­pentane mol­ecules are linked by N—H⋯N hydrogen bonds into a three-dimensional network. The spaces within the network are occupied by the thio­phene-2-carbaldehyde mol­ecules. The thio­phene-2-carbaldehyde unit is disordered over two positions of equal occupancy. The crystal studied was found to be a non-morohedral twin with two minor twin components of 18.4 and 9.7%.

The title mol­ecule, C21H28O5, is composed of three six-membered rings (A/B/C) and a five-membered ring (D). Ring A adopts a 1α-sofa conformation, while rings B and C adopt chair conformations. Cyclo­pentane ring D adopts a 14α-envelope conformation. In the crystal, O—H⋯O hydrogen bonds lead to the formation of ribbons running along the a axis. The structure is further consolidated by C—H⋯O inter­actions, which link the molecules head-to-tail into ribbons along the a axis.

The title compound, C8H14O4, is an isolation product of the aerial parts of Senecio desfontanei. The acetic acid group is oriented at a dihedral angle of 48.03 (9)° with respect to the basal plane of the cyclo­hexane-1,4-diol chair. An intra­molecular O—H⋯O hydrogen bond generates an S(6) ring with an envelope conformation. In the crystal, mol­ecules are linked by O—H⋯O hydrogen bonds, resulting in R 3 3(20) ring motifs and C(2) O—H⋯O—H⋯O—H⋯ chains. Overall, a three-dimensional polymeric network arises. A C—H⋯O contact is also present.

In the title compound, C20H22O5, an S(6) ring motif is formed by an intra­molecular C—H⋯O hydrogen bond, which contributes to the stabilization of the mol­ecule. In the xanthene system, the cyclo­hexane ring adopts a chair conformation, the cyclo­hexene ring adopts a half-boat conformation and the tetra­hydro­pyran ring adopts a half-chair conformation. The mean plane of the four essentially planar atoms of the tetra­hydro­pyran ring [r.m.s deviation = 0.092 (1) Å] forms a dihedral angle of 64.13 (6)° with the mean plane of the meth­oxy­phenyl group. In the crystal, inter­molecular O—H⋯O and weak C—H⋯O hydrogen bonds link mol­ecules into chains along the a axis, which are further stabilized by C—H⋯π inter­actions.

In the title compound, C20H22O5, the tetra­hydro­pyran, cyclo­hexene and cyclo­hexane rings of the xanthene ring system adopt half-chair, half-boat and chair conformations, respectively. The mean plane of the four roughly planar atoms of the tetra­hydro­pyran ring (r.m.s. deviation = 0.111 Å) forms a dihedral angle of 82.91 (4)° with the meth­oxy­benzene group. In the crystal, mol­ecules are linked via O—H⋯O and C—H⋯O hydrogen bonds into sheets lying parallel to the ac plane. The crystal is further consolidated by weak C—H⋯π inter­actions.

In the title compound, C19H19ClO4, the central fused ring and the attached cyclo­hexene ring adopt envelope conformations, while the cyclo­hexane ring adopts a chair conformation. The crystal packing is stabilized by O—H⋯O hydrogen bonds, which link the mol­ecules into a chain along the b axis. Weak C—H⋯O bonds also occur.

The title compound, C21H24N2O2, is a phenyl hydrazine derivative of the well known anthelminthic agent α-santonin, which is composed of three fused rings (benzodieneone, cyclo­hexane and γ-lactone). The cyclo­hexa­dienone ring adopts a boat conformation, the cyclo­hexane ring is in a chair conformation and the trans-fused γ-lactone ring adopts a C-envelope conformation. In the crystal, mol­ecules are linked by N—H⋯O and C—H⋯O hydrogen bonds, forming chains along the a axis.

The asymmetric unit of the title compound, C23H22N2O2, contains two independent mol­ecules, A and B. The cyclo­hexane ring of mol­ecule B is disordered, with occupancies for the major and minor conformers of 0.570 (9) and 0.430 (9), respectively. The cyclo­hexane ring adopts a boat conformation in mol­ecule A and in the major conformer of mol­ecule B, and a chair conformation in the minor conformer of mol­ecule B. In both independent mol­ecules, one of the dihydro­pyran rings adopts a boat conformation while the other is in a half-chair conformation. The dihedral angle between the pyrazole and phenyl rings is 16.0 (1)° in mol­ecule A and 12.9 (1)° in mol­ecule B. The crystal packing is stabilized by C—H⋯O and C—H⋯N inter­molecular hydrogen bonds.

In the title compound, C30H22BrNO2, the cyclo­pentane ring of the dihydro­acenaphthyl­ene group and the pyrrolidine ring are both in envelope conformations with the spiro C atom and N atom, respectively, as the flap atom. The cyclo­pentane ring of the indane group adopts a half-chair conformation. A weak intra­molecular C—H⋯O hydrogen bond forms an S(8) ring motif. The naphthalene ring system of the dihydro­acenaphthyl­ene group forms dihedral angles of 41.76 (6) and 42.17 (6)° with the benzene ring of the bromo­phenyl group and the benzene ring of the indane group, respectively. The dihedral angle between the two benzene rings is 83.92 (7)°. In the crystal, mol­ecules are linked by weak C—H⋯O and C—H⋯N hydrogen bonds into a two-dimensional network parallel to the ac plane. Weak C—H⋯π inter­actions are also observed.

The title compound, C19H29O4, was synthesized from 9α-hy­droxy­parthenolide (9α-hy­droxy-4,8-dimethyl-12-methylen-3,14-dioxatricyclo­[9.3.0.02,4]tetra­dec-7-en-13-one), which was isolated from the chloro­form extract of the aerial parts of Anvillea radiata. The mol­ecule is built up from two fused five- and ten-membered rings with the pyrrolidin-1-ylmethyl group as a substituent. The five-membered lactone ring has an envelope conformation, whereas the ten-membered and pyrrolidine rings display approximate chair–chair and twisted conformations, respectively. The dihedral angle between the ten-membered ring and the lactone ring is 18.01 (19)°. An intra­molecular O—H⋯N hydrogen bond occurs. The crystal structure is stabilized by weak inter­molecular C—H⋯O hydrogen-bonding inter­actions.

The title compound, C21H23NO3, is a phenyl­imine derivative of the well known anthelmintic agent α-santonin. The trans-fused cyclo­hexane and γ-lactone rings of the α-santonin ring system adopt chair and envelope conformations, respectively, whereas the hexa­diene ring is approximately planar [maximum deviation = 0.029 (4) Å] and forms a dihedral angle of 62.30 (11)° with the benzene ring. An intra­molecular O—H⋯N hydrogen bond is observed.

In the title mol­ecule, C21H20N2O4, the dihedral angle between the phenol ring and the isoindole-1,3-dione mean plane is 69.79 (6)°. The cyclo­hexane ring adopts a chair conformation. Weak inter­molecular O—H⋯O and O—H⋯N inter­actions feature as part of the crystal packing.

The title compound, C15H18O3, was synthesized from 9α-hy­droxy­parthenolide (9α-hy­droxy-4,8-dimethyl-12-methylen-3,14-dioxa-tricyclo­[9.3.0.02,4]tetra­dec-7-en-13-one), which was isolated from the chloro­form extract of the aerial parts of Anvillea radiata. The seven-membered ring of the title compound shows a chair conformation, while the five-membered rings exibit different conformations, viz a twisted one for the lactone ring and an envelope conformation for the other five-membered ring with the C atom closest to the hydroxy group forming the flap. In the crystal, O—H⋯O hydrogen bonds connect mol­ecules into dimers that are inter­connected by C—H⋯O inter­actions, producing supramolecular chains along the b axis.

In the title compound, C26H24BrNO5·H2O, a synthetic analogue of natural flavagline, the cyclo­pentane ring adopts an envelope conformation (the flap atom bearing the phenyl group) and the vicinal phenyl and bromo­phenyl groups are slightly shifted relative to each other [CPh—C—C—CPhBr = 36.3 (2)°]. Intra­molecular N—H⋯O and C—H⋯O hydrogen bonds form S(5) motifs. In the crystal, the organic and the water mol­ecules are linked by an O—H⋯O hydrogen bond. Pairs of organic and water mol­ecules, located about inversion centers, inter­act through O—H⋯O hydrogen bonds, forming R 4 4(20) and R 4 4(26) motifs, which together lead to C 2 2(9) motifs. The crystal packing is also characterized by N—H⋯O and C—H⋯O hydrogen bonds between neighbouring organic mol­ecules, forming R 2 2(10) and R 2 2(18) motifs, respectively.

The title compound, C15H20O4, was synthesized from 9α-hy­droxy­parthenolide (9α-hy­droxy-4,8-dimethyl-12-methyl­ene-3,14-dioxatricyclo­[9.3.0.02,4]tetra­dec-7-en-13-one), which was isolated from the chloro­form extract of the aerial parts of Anvillea radiata. The seven-membered ring has a chair conformation, while the five-membered rings display twisted conformations. The dihedral angle between the seven-membered ring and the lactone ring is 21.69 (10)°. In the crystal, mol­ecules are linked into chains propagating along the c axis by inter­molecular O—H⋯O hydrogen bonds; an intra­molecular O—H⋯O link also occurs.