5-Bromospiro[1,2-dioxane-4,4′-tricyclo[4.3.1.13,8]undecane]-3′-ol

The title compound, C14H21BrO3, comprises a seven- (C7) and three six-membered (1 × O2C4 and 2 × C6) rings, and each adopts a conformation based on a chair. Stability to the molecular structure is afforded by an intramolecular O—H⋯Br hydrogen bond. In the crystal structure, molecules are arranged into a helical supramolecular chain along the b axis, linked by C—H⋯O interactions, where the O-atom acceptor is one of the dioxane O atoms. The crystal studied was found to be a racemic twin. The major component was present 94% of the time.

The title compound, C 14 H 21 BrO 3 , comprises a seven-(C 7 ) and three six-membered (1 Â O 2 C 4 and 2 Â C 6 ) rings, and each adopts a conformation based on a chair. Stability to the molecular structure is afforded by an intramolecular O-HÁ Á ÁBr hydrogen bond. In the crystal structure, molecules are arranged into a helical supramolecular chain along the b axis, linked by C-HÁ Á ÁO interactions, where the O-atom acceptor is one of the dioxane O atoms. The crystal studied was found to be a racemic twin. The major component was present 94% of the time.
The molecular structure of (I), Fig. 2, features a close intramolecular O-H···Br hydrogen bond as both substituents lie to the same side of the molecule, Table 1. This interaction closes a six-membered {···HOC 3 Br} ring with a half-chair conformation. The six-membered O 2 C 4 ring has a twisted chair conformation and the bromide occupies an axial position.
The two six-membered C 6 rings share the C7, C11, and C12 atoms, and each has a slightly twisted chair conformation. The hydroxyl group occupies a bisectional position relative to the ring to which it is connected. Finally, the seven-membered ring comprising the C1,C5-C10 atoms has a distorted chair conformation with the C5 and C8 atoms occupying positions above and below the plane defined by the remaining five atoms. In the crystal structure, the primary intermolecular interactions are of the type C-H···O, Table 1. The dioxane-O1 atom forms two close C-H···O contacts to form a supramolecular helical chain aligned along [010], Fig. 3 and Table 1.

Experimental
Referring to the reaction scheme shown in Fig. 1, to a stirred solution of 1 (200 mg, 0.91 mmol) in acetone (5 ml) was added water (180 mg, 10 mmol) and N-bromosuccinimde (219 mg, 1.23 mmol). The mixture was stirred at ambient temperature until TLC indicated complete consumption of starting material (ca 3 h). The reaction was then diluted with CH 2 Cl 2 (50 ml), washed with sat. NaHCO 3 solution (2 x 20 ml), and dried (Na 2 SO 4 ). The solvent was removed in vacuo yielding a crude multi-component mixture which was purified by flash chromatography eluting with 3:1 CH 2 Cl 2 /hexane. Fractions of interest (R f 0.20 in 3:1 CH 2 Cl 2 /hexane) were combined and concentrated giving a solid white residue, which was recrystallized from a slowly evaporating a 1:1 mixture of dichloromethane/heptane producing the title compound (I) as colourless needles.

Refinement
Carbon-bound H-atoms were placed in calculated positions (C-H 0.98-0.99 Å) and were included in the refinement in the riding model approximation with U iso (H) set to 1.2U eq (C). The O-bound H-atom was located in a difference Fourier map and was refined with an O-H restraint of 0.840±0.001 Å, and with U iso (H) = 1.5U eq (O). The structure was refined as a racemic twin precluding the determination of the absolute structure. Fig. 1. Reaction scheme. Fig. 2. Molecular structure of (I) showing atom-labelling scheme and displacement ellipsoids at the 50% probability level.