O-Ethyl S-{(S)-1-oxo-1-[(R)-2-oxo-4-phenyloxazolidin-3-yl]propan-2-yl} carbonodithioate

In the title compound, C15H17NO4S2, synthesized by addition of O-ethylxanthic acid potassium salt to a diastereomeric mixture of (4R)-3-(2-chloropropanoyl)-4-phenyloxazolidin-2-one, the oxazolidinone ring has a twist conformation on the C—C bond. The phenyl ring is inclined to the mean plane of the oxazolidinone ring by 76.4 (3)°. In the chain the methine H atom is involved in a C—H⋯S and a C—H⋯O intramolecular interaction. In the crystal, molecules are linked by C—H⋯π interactions, forming chains along [001]. The S configuration at the C atom to which the xanthate group is attached was determined by comparison to the known R configuration of the C atom to which the phenyl group is attached.

In the title compound, C 15 H 17 NO 4 S 2 , synthesized by addition of O-ethylxanthic acid potassium salt to a diastereomeric mixture of (4R)-3-(2-chloropropanoyl)-4-phenyloxazolidin-2one, the oxazolidinone ring has a twist conformation on the C-C bond. The phenyl ring is inclined to the mean plane of the oxazolidinone ring by 76.4 (3) . In the chain the methine H atom is involved in a C-HÁ Á ÁS and a C-HÁ Á ÁO intramolecular interaction. In the crystal, molecules are linked by C-HÁ Á Á interactions, forming chains along [001]. The S configuration at the C atom to which the xanthate group is attached was determined by comparison to the known R configuration of the C atom to which the phenyl group is attached.
Financial support from CONACYT (project No. 183980) and CIC-UMSNH is gratefully acknowledged. JM is grateful to CONACYT for a scholarship (grant: 186053) to support his studies. YLC is grateful to CONACYT (project No. 183980) for providing a license to use the Cambridge Structural

Comment
Oxazolidinones and their derivatives show interesting chemical and biological activities. The use of chiral oxazolidinones auxiliaries in asymmetric synthesis has found wide application in a variety of stereoselective reactions over the last two decades (Evans, 1982;Ager et al., 1997). In addition oxazolidinonas represent a novel class of synthetic antimicrobial agents, the most promising feature of these compounds is their oral activity against multidrug-resistant Gram-positive bacteria which have created tremendous therapeutic problems in recent years (Müller et al., 1999). Based on this, and as part of our ongoing research program directed toward the synthesis of novel heterocyclic compounds (see for example: López-Ruiz et al., 2011) we report herein on the use of (R)-4-phenyloxazolidin-2-one for the synthesis of the title xanthate-oxazilidinone derivative, which has potential applications as a chiral auxiliary in asymmetric reactions.

Experimental
For the preparation of the title compound, a solution of (4R)-4-phenyloxazolidin-2-one (10.70 mmol) in distilled THF (25 ml) was cooled to 195 K under a nitrogen atmosphere, and a solution of n-butyllithium in hexane (12.95 mmol) was added dropwise. After 2-chloropropanoyl chloride (10.79 mmol) was introduced dropwise and stirring was continued at 195 K for 6 h. Then the reaction mixture was diluted with saturated solution of NH 3 SO 4 and extracted with dichloromethane (3 × 10 ml). The combined organic layers were washed with water and brine, dried over anhydrous Na 2 SO 4 and concentrated under vacuum. Purification by chromatography column on silica gel (eluent: hexane/ethyl acetate 9:1) gave the diastereomeric mixture of (4R)-3-(2-Chloropropanoyl)-4-phenyloxazolidin-2-one in 98% yield. To a solution of this diastereomeric mixture (31.19 mmol) in acetone at 273 K was added the O-Ethylxanthic acid potassium salt (46.78 mmol) and the reaction was stirred at room temperature for 12 h. Then the reaction mixture was diluted with a saturated solution of NH 3 SO 4 and extracted with dichloromethane (3 × 10 ml). The organic layer was dried over anhydrous Na 2 SO 4 and concentrated under vacuum. Purification by chromatography column on silica gel (eluent: hexane/ethyl acetate 9:1) gave the diastereomeric mixture of (4R)-3-((2R)-(2-O-Ethyl carbonodithioate) propanoyl)-4-phenyloxazolidin-2-one in a 77% of yield. Block-like colourless crystals of the title compound were obtained by slow evaporation of an hexane/ethyl acetate (9:1) solution. Spectroscopic data for the title compound are available in the archived CIF.

Refinement
The H atoms were inlcuded in calculated positions and treated as riding atoms: C-H = 0.93 -0.98 Å with U iso (H) = 1.5U eq (C-methyl) and = 1.2U eq (C) for other H atoms.

Figure 1
The molecular structure of the title molecule, with atom labelling. Displacement ellipsoids are drawn at the 50% probability level.

Figure 2
The crystal packing of the title compound, viewed along the a axis. The dashed lines indicate the C-H···π interactions (see Table 1 for details; H atoms not involved in these interactions have been omitted for clarity). where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.38 e Å −3 Δρ min = −0.35 e Å −3 Absolute structure: Flack (1983), 6968 Friedel pairs Absolute structure parameter: 0.08 (18) Special details Experimental. Spectroscopic data for the title compound: 1 H NMR (400 MHz, CDCl 3 )δ: 7.2 (m, 5H, CH, arom), 5.6 (q, 1H, CH (H-4), J= 7.3 Hz), 5.4 (dd, CH (H-9), J 1 = 3.2 Hz, J 2 =8.6 Hz), 4.7 (t, 1H (H-8a), CH 2 , J= 8.8 Hz), 4.6 (m, 2H, CH 2 (H-2) Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'s 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 > 2σ(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.