Vieillardiixanthone B.

THE TITLE COMPOUND [SYSTEMATIC NAME: 1,5-dihydr-oxy-3,6-dimeth-oxy-4-(2-methyl-but-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 mol-ecule are approximately coplanar, with an r.m.s. deviation of 0.0372†(2)†à for the plane through the 14 non-H atoms. The O atoms of the two hydr-oxy substituents also lie close to this plane with deviations of 0.0669†(2) and 0.1122†(2)†à , respectively. The 1,1-dimethyl-2-propenyl substituent is in a (-)-anti-clinal conformation. Intra-molecular O-H⋯O hydrogen bonds generate S(5) and S(6) ring motifs. In the crystal, mol-ecules are linked into infinite chains along [010] by O-H⋯O hydrogen bonds and weak C-H⋯O inter-actions. π-π inter-actions with centroid-centroid distances of 3.6172†(10) and 3.6815†(10)†à are also observed.