2-Isopropyl-5-methylcyclohexyl 5-acetoxy-1,3-oxathiolane-2-carboxylate

In the title compound, C16H26O5S, the oxathiolane ring adopts an envelope conformation, with the S atom 0.793 (3) Å out of the mean plane of the remaining four atoms. The cyclohexane ring of the menthol fragment adopts an almost ideal chair conformation, with all substituents in the equatorial positions. In the crystal, relatively strong, short and linear C—H⋯O hydrogen bonds link the molecules into the chains along [100] direction. The chains are packed into the crystal structure by means of weak dispersive interactions. Intermolecular C—H⋯S interactions are also observed.

In the title compound, C 16 H 26 O 5 S, the oxathiolane ring adopts an envelope conformation, with the S atom 0.793 (3) Å out of the mean plane of the remaining four atoms. The cyclohexane ring of the menthol fragment adopts an almost ideal chair conformation, with all substituents in the equatorial positions. In the crystal, relatively strong, short and linear C-HÁ Á ÁO hydrogen bonds link the molecules into the chains along [100] direction. The chains are packed into the crystal structure by means of weak dispersive interactions. Intermolecular C-HÁ Á ÁS interactions are also observed.

Related literature
The title compound is a drug intermediate of lamivudine, a reverse transcriptase inhibitor used in the treatment of HIV infections. For the structures of lamivudine and its hydrate have been studied, see: Harris et al. (1997). For the identification of lamivudine conformers by Raman scattering measurements and quantum chemical calculations, see: Pereira et al. (2007). For asymmetry parameters, see: Duax & Norton (1975). For a description of the Cambridge Structural Database, see: Allen (2002 Table 1 Hydrogen-bond geometry (Å , ). Symmetry codes: (i) x þ 1; y; z; (ii) x À 1 2 ; Ày þ 3 2 ; Àz þ 1.
In the crystal structure relatively strong (short and directional) C13-H13···O12 i hydrogen bonds join the molecules into the infinite chains along [100]. These chain in turn are organized into the crystal structure by weak van der Waals -type interactions (Table 1, Fig. 2).

Experimental
To a mixture of L-menthyl-5-hydroxy-1,3-oxathiolane-2-carboxylate (1.5 g, 5.2 m mol) in pyridine (30 ml), acetic anhydride (6.4 ml) was added slowly at 273 K (Fig. 4). The mixture was allowed to attain room temperature and stirred over night, then quenched to ice cold water and extracted with ethyl acetate. The organic layer was concentrated under vacuum to obtain the product. X-ray quality crystals were grown from slow evaporation of methanol solution (m.p.: 333-335 K).

Refinement
Positional parameters of the hydrogen atoms were freely refined, the U iso values of these atoms were set at 1.2 (1.5 for methyl groups) times U eq of their carrier carbon atom. Fig. 1. Anisotropic ellipsoid representation of the compound I together with atom labelling scheme. The ellipsoids are drawn at 50% probability level, hydrogen atoms are depicted as spheres with arbitrary radii.