The structures of two derivatives of bicyclo[3,3,1]nonane-2,4,9-trione. A natural product: clusianone, C₃₃H₄₂O₄, and trimethylated catechinic acid, C₁₈H₂₀O₆

Abstract

The structures of two derivatives of bicyclo[3,3,1]nonane-2,4,9-trione were solved by direct methods. The structures of clusianone, C33H4204, and trimethylated catechinic acid, C1sH2006, were refined by standard least-squares techniques to weighted R(F) values of 0-038 and 0.046 respectively using diffractometer data. The two molecules are compared and unusually long C(sp3)-C(sp 3) bonds are discussed. Clusianone contains a 1"603 (4) A carbon--carbon bond.

Natural polyprenylated benzophenones: keto-enol tautomerism and stereochemistry

“…Opposed behaviours were previously reported in crystal structures of clusianone 27 and epiclusianone, 17 two related polyprenylated benzophenones presenting the same moiety involved in the tautomerism, where the tautomers that presented the highest relative contribution to hybrid structure were the C10=O2/C2-O3-H2 and C10=O2/C4-O1-H2 forms, respectively. Comparing the lengths of bonds into delocalized system, it was possible to find crucial differences between (a) and clusianone/epiclusianone.…”

“…The highest deviation from the least squares plane passing through the six cyclic atoms above mentioned is -0.046(3) Å for H2, showing that such system is practically planar. Furthermore, the O1…O2 separation is 2.390(4) Å, having an angle of 155(5)° between O2-H2…O1, being that such distance between the O-atoms is slightly shorter than that found in similar benzophenones as clusianone (2.418 Å) 27 and epiclusianone (2.430(4) Å). 17 The strong intramolecular H-bond O2-H2...O1 can also explain significant valence angles deviances.…”

“…Comparing the lengths of bonds into delocalized system, it was possible to find crucial differences between (a) and clusianone/epiclusianone. The lengths of the bonds equivalent to (a) C3=C10, O3=C2, C2-C3 and O2-C10 are respectively 1.448, 1.304, 1.388 and 1.266 Å in clusianone, 27 and those equivalent to (a) C3=C10, O1=C4, C3-C4 and O2-C10 are respectively 1.449(6), 1.299(6), 1.380(6) and 1.268(6) Å in epiclusianone. 17 Considering the first two bonds, C3=C10 and O3=C2 for clusianone and C3=C10 and O1=C4 for epiclusianone, the values of lengths have increased 0.05(1) and 0.02(1) Å, respectively, in comparison with the respective ones determined for (a), whereas the last two bond distances, C2-C3 and O2-C10 for clusianone and C3-C4 and O2-C10 for epiclusianone, have respectively decreased 0.05(2) and 0.03(2) Å when compared with the bond lengths equivalent in (a).…”

“…In clusianone, the configuration in the C7 atom states that C24-C28 prenyl group is below C1-C5-C7 plane, in an equatorial orientation. 27 The explanation for this differential H-bond localization can be in the stereochemistry of C7 atom. In the cases of epiclusianone and (a), the axial position of prenyl group approximates the C25=C26 and C2=O3 groups (Figure 2), favoring an intramolecular dipolar interaction between such ones.…”

“…So, the intramolecular contact cited in epiclusianone and (a) is unavailable in clusianone, and the electronic deficiency is not achieved in C2=O3 group. As result, the O3 atom bonds covalently to H2 atom and the benzoyl group rotates 180° in order to stabilize the structure via O3-H2…O2 H bond, as described by McCandlish et al 27 Selected bond lengths and angles of (a) are available in supplementary material. The intra-molecular geometry of (a) was analyzed using MOGUL, 25 a knowledge base of molecular geometry derived from Cambridge Structural Database CSD, 26 that provides access to information on the preferred values of bond lengths, valence angles and acyclic torsion angles.…”