(1RS,2RS,3SR,5RS,7RS)-2,5-Dichloro-8-oxabicyclo[5.1.0]octan-3-ol

In the title compound, C7H10Cl2O2, the seven-membered ring displays a chair conformation. In the crystal, the hydroxy H atom is equally disordered over two orientations, and links with an adjacent molecule via an O—H⋯O hydrogen bond in both cases. Weak intermolecular C—H⋯O hydrogen bonding is also a feature of the crystal structure.

In the title compound, C 7 H 10 Cl 2 O 2 , the seven-membered ring displays a chair conformation. In the crystal, the hydroxy H atom is equally disordered over two orientations, and links with an adjacent molecule via an O-HÁ Á ÁO hydrogen bond in both cases. Weak intermolecular C-HÁ Á ÁO hydrogen bonding is also a feature of the crystal structure.

Experimental
Crystal data

Structure Reports Online
Unsaturated bicyclic endopexide, (1), (Scheme 1) was synthesized by the literature method . Reaction of endoperoxide, (1), by heating at 453 (5) K gave a mixture of products (Scheme 1). The title compound, (2), was isolated from these mixtures. The other products were not identified. According to the NMR data of dichloride, (2), it was not easy to establish the exact configuration of the molecule. Therefore, the exact structure of dichloride, (2), was determined by X-ray single crystal analysis.
To rationalize the formation of dichloride, (2), we propose the following reaction mechanism as favourable mechanism (Scheme 1). Bis-epoxide, (3) In the crystal, intermolecular O-H···O and C-H···O hydrogen bonds link the molecules into a three-dimensional network (Table 1 and Fig. 2).

Experimental
For the preparation of the title compound, a mixture of endoproxide (0.5 g, 2.6 mmol) and benzene (5 ml) was placed into a test tube, sealed under vacuum and heated at 453 (5) K for 3 d. After cooling to room temperature, the solvent was evaporated. The residue was submitted to column chromatography (silica gel, 90 g) with AcOEt/hexane (1:6) as eluant.

Refinement
H1, H7, H21, H22 and H41, H42 atoms were positioned geometrically with C-H = 0.98 and 0.97 Å, respectively, and constrained to ride on their parent atoms, with U iso (H) = 1.2U eq (C). The remaining H-atoms were located in a difference supplementary materials sup-2 Fourier map and refined isotropically. The H atom of the OH group was disordered over two orientations. During the refinement process, the disordered H2A and H2B atoms were refined with equal occupancies. Fig. 1. The molecular structure of the title molecule with the atom-numbering scheme. Displacement ellipsoids are drawn at the 40% probability level. bsorption correction: multi-scan (Blessing, 1995) h = −27→27

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
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.

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