(2R,3R,4aS,6S,7S,8aS)-4a-Fluoro-8a-hydroxyperhydronaphthalene-2,3,6,7-tetrayl tetraacetate

The title compound, C18H25FO9, exhibits a similar unit cell and packing to the α polymorph of axial 4a,8a-dihydroxyperhydronaphthalene-2,3,6,7-tetrayl tetraacetate. The carbonyl O atoms of two of the four acetate groups in the molecule are disordered over two sites with occupancy ratios of 0.59 (4):0.41 (4) and 0.57 (6):0.43 (6). Crystal packing is effected via intermolecular O—H⋯O hydrogen bonds, which link the tetraacetate molecules into tapes along the c axis.

The title compound, C 18 H 25 FO 9 , exhibits a similar unit cell and packing to the polymorph of axial 4a,8a-dihydroxyperhydronaphthalene-2,3,6,7-tetrayl tetraacetate. The carbonyl O atoms of two of the four acetate groups in the molecule are disordered over two sites with occupancy ratios of 0.59 (4):0.41 (4) and 0.57 (6):0.43 (6). Crystal packing is effected via intermolecular O-HÁ Á ÁO hydrogen bonds, which link the tetraacetate molecules into tapes along the c axis.
Quite akin to that observed in the α form of 3, the carbonyl O atoms (O7 and O9) of two acetate groups in the asymmetric unit of 1 are disordered over two sites, A and B, having occupancy factors of about 0.60 and 0.40 respectively (Fig. 1).
The tertiary hydroxyl group in 1 does not engage itself as an intramolecular O-H···O hydrogen bond donor to either of the flanking 1,3-syndiaxial oxygen acceptors, O2 and O4.

Experimental
The title compound was prepared by acetylating the monofluoropentol 2 at ambient temperature in presence of acetic anhydride and 4-Dimethylaminopyridine (Mehta & Sen, 2010c). Single crystals of 1, suitable for X-ray diffraction studies, were grown by slow solvent evaporation of its solution in 1:1 dichloromethane and petroleum ether under ambient temperature and pressure.

Refinement
The methine (CH) and methylene (CH 2 ) H atoms were placed in geometrically idealized positions and allowed to ride on their parent atoms with C-H distances in the range 0.97-0.98 Å and U iso (H) = 1.2U eq (C). The CH 3 and OH hydrogen atoms were constrained to an ideal geometry with C-H distances as 0.96 Å and U iso (H) = 1.5U eq (C), and O-H distances fixed at 0.82 Å and U iso (H) = 1.5U eq (O). During refinement, each methyl and hydroxyl group was however allowed to rotate freely about its C-C and C-O bond respectively. Due to the absence of any significant anomalous scatterers (Z>Si) in 1, attempts to refine the Flack (Flack, 1983) parameter led to an inconclusive value of -0.8 (13) (Flack & Bernardinelli, supplementary materials sup-2 2000). Therefore the intensities of the Friedel pairs (1828) were averaged prior to merging of data in Cc, so that the reported value of R int corresponds to subsequent merging of equivalent reflections in this space group. Fig. 1. View of the tetra-acetate 1, with the atom numbering scheme. Displacement ellipsoids for non-H atoms are drawn at the 50% probability level. H atoms are shown as small spheres of arbitrary radii.  (2R,3R,4aS,6S,7S,8aS)-4a-Fluoro-8a-hydroxyperhydronaphthalene-2,3,6,7-tetrayl tetraacetate