(2SR,3RS)-Methyl 2-(adamantan-1-yl)-3-phenylsulfonyl-3-(pyridin-2-ylsulfanyl)propanoate dichloromethane hemisolvate

The title compound, C25H29NO4S2 0.5CH2Cl2, was obtained as a racemate. The pyridine and phenyl rings are arranged face-to-face, giving a weak intramolecular π–π interaction [centroid–centroid separation = 3.759 (3) Å]. These interactions are extended intermolecularly, forming chains of stacked rings along [001] with separations of 3.859 (3) and 3.916 (3) Å. The solvent used for crystallization, CH2Cl2, is located in voids between the chains of molecules, with a site occupancy of 0.5.

We gratefully acknowledge financial support of the Facultad de Ciencias Químicas, Benemé rita Universidad Autó noma de Puebla.
Compounds containing adamantyl radicals are useful catalysts for many chemical reactions, such as the refining of halogen atoms and preparation of heterogeneous bimetallic catalysts (Taoufik et al., 1999). The rigid, spherical shape of adamantane reduces interchain interactions in polymers and may help with the synthesis of poly(p-phenylenevinylene) (PPV) derivatives (Jeong et al., 2002). Adamantane-containing molecules have also been found to have antiviral activity (Kadi et al., 2010;Papanastasiou et al., 2010) and have been used in the treatment of influenza A (Zarubaev et al., 2010), HIV-1, leukemia and deafness (Spasov et al., 2000).
Alkyl radicals derived from O-acyl esters of N-hydroxy-2-thiopyridone (a.k.a. Barton esters) are nucleophilic, so treatment with electron-deficient olefins such as vinyl sulfones generates the corresponding addition products (alkyl 2-pyridyl sulfides) effectively. Derivatives generated from adamantylcarboxylic acid using the Barton method (Togo, 2004) have potential biological activity. Crystallization of the racemate in the title compound is similar to an anti addition of the Barton ester to the olefin.

Experimental
To a solution of 1,3-dicyclohexylcarbodiimide (DCC, 2 mmol) in CH 2 Cl 2 (8 ml) was added N-hydroxy-2-thiopyridone (2.2 mmol) under an argon atmosphere. The solution was protected from light with aluminium foil and kept at 273 K in an ice bath. Adamantylcarboxylic acid (2 mmol) dissolved in CH 2 Cl 2 was added dropwise to the solution. After the addition, the mixture was allowed to reach room temperature and further stirred for a period of 1.5 h. The resulting yellow solid was filtered on a bed of silica gel and washed with dry CH 2 Cl 2 (all in dark). The filtrate was concentrated under reduced pressure, to give a crystalline solid. m.p. 164-166°C (compound 1 in Fig. 1). O-acyl ester 1 (1 mmol) was dissolved in CH 2 Cl 2 (5 ml) under an argon atmosphere and (E)-methyl-3-(phenylsulfonyl)acrylate 2 (1.1 mmol) was added to the yellowish solution.
The mixture was irradiated with a tungsten lamp (150 W), following the reaction by TLC. The products were purified by chromatography on silica gel (eluent: hexane:ethyl-acetate, 7:3). A white crystalline solid was obtained with a yield of 88%.

Refinement
Crystals of the title hemisolvate are stable in air for months, but solvent loss occurs under X-ray irradiation. A complete data set for the studied crystal was however collected over a period of 54 h, during which the intensity decayed by ca. 40%.
Isotropic displacement parameters for H atoms were computed as U iso (H) = 1.5 U eq (carrier C) for the methyl group and U iso (H) = 1.2 U eq (carrier C) for other H atoms.