Absolute configuration of xerophenone A

The title compound, C(33)H(42)O(5), known as xerophenone A {systematic name: (1R,3R,4R,6S,8E,10R)-10-hy-droxy-8-[hy-droxy(phen-yl)methyl-ene]-4-methyl-1,6-bis-(3-methyl-but-2-en-1-yl)-3-(3-methyl-but-3-en-1-yl)-11-oxatricyclo-[4.3.1.1(4,10)]undecane-7,9-dione} is a naturally occurring rearranged benzophenone compound which was isolated from the twigs of Garcinia propinqua. The absolute configuration was determined by refining the Flack parameter to 0.18 (16). The absolute configurations at positions 1, 3, 4, 6 and 10 of the xerophenone A are R, R, R, S and R. In the mol-ecule, the cyclo-hexane-1,3-dione, tetra-hydro-2H-pyran and tetra-hydro-furan rings adopt twisted boat, standard chair and envelope conformations, respectively. The 3-methyl-but-3-en-1-yl substituent is disordered over two sets of sites in a 0.771 (11):0.229 (11) ratio. An intra-molecular O-H⋯O hydrogen bond generates an S(6) ring motif. In the crystal, mol-ecules are linked by O-H⋯O and weak C-H⋯O inter-actions into a chain along the a axis. A very weak C-H⋯π inter-action and C⋯O short contact [2.989 (2) Å] are also present.