5-Hydroxy-7-methoxy-4H-chromen-4-one

The molecular conformation of the title compound, C10H8O4, isolated from Laretia acualis, is stabilized by a strong intramolecular hydrogen bond between the hydroxyl and carbonyl groups. The crystal packing shows π–π stacking interactions. The chromene (4H-1-benzopyran-4-one) unit is essentially planar.

The molecular conformation of the title compound, C 10 H 8 O 4 , isolated from Laretia acualis, is stabilized by a strong intramolecular hydrogen bond between the hydroxyl and carbonyl groups. The crystal packing showsstacking interactions. The chromene (4H-1-benzopyran-4-one) unit is essentially planar.
LAL thanks the Fondo Nacional de Desarrollo Científico y Tecnoló gico de Chile for grant 1060339. We thank the Spanish Research Council (CSIC) for providing us with a free-ofcharge licence for the Cambridge Structural Database.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: BT2661). The title compound was originally isolated from Artemisia campestris (maritima) (Vasconcelos et al., 1998) and later from Laretia acualis (Cav.) which is known in Chile as "Llareta de la zona central", is a yellowish-green, compact resinous cushion shrub, which grows in the high Andes of Chile. Whole plant infusions are widely used as diabetes treatment in folk medicine (Wickens, 1995). Chromene derivatives exhibits a wide spectrum of biological activity, including spasmolytic, anti-arrhytmic, cardionthonic, antiviral, anticancer and alkylating properties (Gabor, 1988;Valenti et al., 1993Valenti et al., , 1998.

Structure Reports Online
The title structure ( Fig.1), consists of a chromene moiety substituted in position 5 and 7 with a hydroxy and methoxy group, respectively. The chromene ring system is essentially planar with maximum deviation of −0.007 (2) Å for C2. The geometrical parameters of the chromene group are comparable to those of related structures reported earlier (Wallet & Cody, 1995). The mean bond distances are: O-Csp 2 1.3552 (17) Å, and aromatic C-C 1.391 (2) Å, while C4=O2 is 1.2531 (18)Å and C2=C3 is essentially a double bond with a distance of 1.330 (2) Å Å. In the crystal structure, the molecular packing is stabilized by intramolecular O-H···O hydrogen bond generating a graph-set motif S(6) (Bernstein et al., 1995) as well as π-π stacking interactions (Table 2).

Experimental
Dried and finely powdered tissues from the aerial parts of Laretia acualis (535 g) were extracted with petrol ether at room temperature. The solvent was evaporated to dryness by vacuum distillation and low temperature, yielding a gum (15 g).
The concentrated petrol ether extract was fractionated on silica gel column with hexane-ethyl acetate mixtures of increasing polarity as elution solvents. The fraction hexane-ethyl acetate 10% (2.45 g) was separated on silica gel using the same elution solvents yielding 45.5 mg of (I)(m.p. 374 K). The title compound was identified by comparing the spectroscopic data with the previously published data (Vasconcelos et al., 1998). Recrystallization from hexane/ethyl acetate (8:2) at room temperature afforded colourless crystals suitable for X-ray diffraction analysis.

Refinement
H atom attached to O3 atom was located in a difference Fourier map and refined isotropically. All other H atoms were positioned geometrically and then treated as riding, with C-H distances of 0.93 (CH) and 0.96 Å (CH 3 ), and U iso (H) = 1.2U eq (C) or U iso (H) = 1.5U eq (C methyl ). Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.