Vieillardiixanthone B

The title compound [systematic name: 1,5-dihydr­oxy-3,6-dimeth­oxy-4-(2-methyl­but-3-en-2-yl)-9H-xanthen-9-one], C(20)H(20)O(6), is a xanthone, which was isolated from the roots of Cratoxylum formosum ssp. pruniflorum. The three rings in the mol­ecule are approximately coplanar, with an r.m.s. deviation of 0.0372 (2) Å for the plane through the 14 non-H atoms. The O atoms of the two hydr­oxy substituents also lie close to this plane with deviations of 0.0669 (2) and 0.1122 (2) Å, respectively. The 1,1-dimethyl-2-propenyl substituent is in a (−)-anti­clinal conformation. Intra­molecular O—H⋯O hydrogen bonds generate S(5) and S(6) ring motifs. In the crystal, mol­ecules are linked into infinite chains along [010] by O—H⋯O hydrogen bonds and weak C—H⋯O inter­actions. π–π inter­actions with centroid–centroid distances of 3.6172 (10) and 3.6815 (10) Å are also observed.