(1R,3R,4R,6S)-4-(7-Methoxy-2-oxo-2H-chromen-6-yl)-1-methyl-3,6-dioxabicyclo[3.1.0]hexan-2-yl acetate

In the title compound, C17H16O7, which was isolated from the leaves of Micromelum integerrimum, the furan ring adopts an envelope conformation with the O atom as the flap. An intramolecular C—H⋯O hydrogen bond occurs. The carbonyl O atom is disordered in a 0.57 (8):0.43 (8) ratio. In the crystal, molecules are linked by weak C—H⋯O hydrogen bonds into a C(10) chain along [010].

Data collection: APEX2 (Bruker, 2008); cell refinement: SAINT (Bruker, 1997); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2007); software used to prepare material for publication: publCIF (Westrip, 2010) and PLATON (Spek, 2009  Micromelum integerrimum is a shrub in the Rutacae family containing the coumarin molecule, micromilin, as the major chemical constituent (Cassady et al., 1979). Many coumarins including micromilin have been extracted from Rutacae plants, and for some their cytotoxicity has been investigated (Sripisut et al., 2012;He et al., 2001). In the attempt to investigate the chemical constitutents of the extract of Micromelum integerrimum leaves collected from Chiang Rai province in the Northern part of Thailand (March 2012), the colourless crystals of the title compound have been isolated and examined.

Experimental
The title compound was obtained from an acetone extract of Micromelum integerrimum leaves (0.55 kg), which are collected from Chiang Rai Province, Thailand. From seven fractions (A-G) yielded by column chromatography using hexanes-acetone, the title compound (295.9 mg) was isolated from fraction D by also column chromatography using 2% acetone-CH 2 Cl 2 . The crystals were then crystallized by slowly evaporation of the solvent.

Refinement
The carbonyl group O atom is disordered over two sets of sites in a 0.57 (8):0.43 (8) ratio.Friedel opposites were merged in the final cycles of refinement as there is no appreciable anomalous scattering at the wavelength used for data collection. H atoms were placed in geometrically idealized positions (C-H= 0.91-1.06 Å, C(methyl)-H=0.96Å and were constrained to ride on their parects atoms with U iso (H)= 1.2U eq (C) and 1.5U eq (C) respectively , except H3, H4, H5, supplementary materials sup-2 Acta Cryst. (2012). E68, o3421-o3422 and H8, were refined freely, with isotropic displacement parameters.

Figure 1
Molecular structure of the title compound. Displacement ellipsoids are drawn at 50% probability level.  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 > σ(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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (