rac-(2R*,3S*,5S*,6R*,7S*,8S*)-7,8-Dichlorobicyclo[2.2.2]octane-2,3,5,6-tetrayl tetraacetate

The title compound, C16H20Cl2O8, contains a central bicyclo[2.2.2]octane skeleton with slightly twisted conformation. In this structure, the C—C bond lengths are in the range 1.525 (2)–1.552 (2) Å. Two sides of this skeleton have cis,cis acetoxy substituents and the Cl atoms have a trans arrangement. An extensive network of weak C—H⋯O interactions stabilizes the crystal structure.

The title compound, C 16 H 20 Cl 2 O 8 , contains a central bicyclo[2.2.2]octane skeleton with slightly twisted conformation. In this structure, the C-C bond lengths are in the range 1.525 (2)-1.552 (2) Å . Two sides of this skeleton have cis,cis acetoxy substituents and the Cl atoms have a trans arrangement. An extensive network of weak C-HÁ Á ÁO interactions stabilizes the crystal structure.
New synthetic methodologies for various inositols and their derivatives have been developed. After this discovery, an enormous increase in the synthesis of cyclitol derivatives (Mehta et al. 2007;Shih et al. 2007;Gültekin et al. 2004;Mehta & Ramesh, 2001;Balcı, 1997;Balcı et al.1990) was observed since these show glycosidase inhibitory properties. More recently, a bridged and bicyclic system, the racemic gluco-configured norbornane has been synthesised and tested as inhibitor of β-glycosidases (Buser & Vasella, 2006). They noticed that the configuration of the hydroxy group play an important role in inhibitor activity. Motivated by the medical value of certain cyclitol derivatives, we were interested in designing a new generation of possible glycosidase inhibitors with the bicyclic structures having bicyclo[2.2.2]octane skeleton.
For the synthesis of isomeric hexols with bicyclo[2.2.2]octane skeleton, the tetracetate 1 was reacted with m-CPBA. The reaction was completed after 21 days by refluxing in chloroform. Recently, we isolated a side product I in 8% yields beside the major product 2 (86%). The structure of the side product was confirmed by NMR-spectroscopic studies. The incorporation of the chlorine atoms into the molecule and their configuration were determined by X-ray diffraction analysis. The title compound (I) C 16 H 20 O 8 Cl 2 contains a central bicyclo[2.2.2]octane skeleton with slightly twisted conformation. In this structure C-C bond lengths are in the range of 1.525 (2)-1.552 (2) Å. Two sides of this skeleton have cis, cis -OAc substituents. In addition to this, Cl atoms have trans stereochemistry at the other side (C7-Cl1=1.796 (2), C8-Cl2=1.798 (2) Å). Intermolecular C-H···O hydrogen bonds are effective in determining the molecular conformation and the crystal structure of the title compound (Table 1).
To test whether the adduct I has been generated by addition of free chlorine to the double bond or by other mechanism, we treated the tetraacetate 1 with chlorine gas for 3 h. The chlorine added to the double bond in 1 in a yield of 80% and gave I, which was identical with the adduct isolated from the epoxidation reaction of 1 as the side product.
To the best of our knowledge, chlorine addition to a double bond during an epoxidation reaction has been not presented in the literature. This reaction can be probably encountered only during those reactions which are completed in 2-3 weeks because of the very slow oxidation of chloroform.