(3aR,4S,7R,7aS)-2-Phenyl-4-propyl-3a,4,7,7a-tetrahydro-1H-4,7-epithioisoindole-1,3-dione 8-oxide

In the tetrahydroisoindole moiety of the title compound, C17H17NO3S, the six-membered ring assumes a boat configuration and the –S=O group bridges the prow and stern of the boat. The phenyl ring is oriented at a dihedral angle of 83.2 (1)° with respect to the pyrrole ring. In the crystal, intermolecular C—H⋯O hydrogen bonds link the molecules into a three-dimensional network. A weak C—H⋯π interaction involving the phenyl ring is also found. The crystal studied was an inversion twin.

In the tetrahydroisoindole moiety of the title compound, C 17 H 17 NO 3 S, the six-membered ring assumes a boat configuration and the -S O group bridges the prow and stern of the boat. The phenyl ring is oriented at a dihedral angle of 83.2 (1) with respect to the pyrrole ring. In the crystal, intermolecular C-HÁ Á ÁO hydrogen bonds link the molecules into a three-dimensional network. A weak C-HÁ Á Á interaction involving the phenyl ring is also found. The crystal studied was an inversion twin.

Comment
Thiophene behaves as the least reactive diene among all aromatic five-membered heterocycles; the presence of 3d orbitals on sulfur contributes to the resonance stability of the thiophene system (Lert & Trindle, 1971). Cycloaddition reactions of thiophene also have limitations therefore its 4 + 2 cycloaddition can occur under following conditions; use of highly reactive dienophiles (Thiemann et al., 1995), enhance electron density on the thiophene by having substituent at position 2 or 5 (Al-Omran et al., 1996), high reaction temperature (Kuhn & Gollnick, 1972) or use of high pressure (Kotsuki et al., 1978). However, the number of publications dealing with the chemistry of thiophene dioxide based new materials, namely, semiconductor organic transistors and light diodes first designed about 13 years ago. New data on the biological activities of some thiophene 1,1-dioxide derivatives were observed in recent years (Thiemann et al., 2009).
Thiophene s-oxides are derivatives of thiophene, which belong to an important group of five-membered heterocyclic compounds having non-aromatic character. Thiophene s-oxides with alkyl groups at positions 2,3,4 and 5 have been the subject of extensive studies in recent past (Rajappa, 1984). Owing to the unique structure combined with high reactivity, they can be used to prepare various heterocyclic systems; therefore, these compounds are useful building blocks in synthetic organic chemistry. In continuation of our research program and following our previous interest in the sytheses of fused heterocyclic compounds using furan (Arslan & Demircan, 2007;Koşar et al., 2006), it has been found that mono alkylated thiophene at position 2 will lead to an excellent building block for the synthesis of the title compound.
The title compound contains two non-planar five-and six-membered rings, which has a pyrrole (C1/N2/C3/C3a/C7a) In the crystal, intermolecular C-H···O hydrogen bonds link the molecules to form a three-dimensional network (Table   1 and Fig. 2). There also exist a weak C-H···π interaction involving the phenyl ring A (C12-C17) ( Table 1).

Experimental
For the preparation of the title compound, BF 3 .Et 2 O (6.1 ml, 47.75 mmol) was added slowly to a solution of 2-propylthiophene (1.00 g, 7.90 mmol) and N-phenylmaleimide (2.06 g, 11.90 mmol) in dry dichloromethane (DCM) (40 ml) under an inert atmosphere at 253 K. The reaction mixture was stirred for 10 min at 253 K, and then a solution of meta chloroperbenzoic acid (m-CPBA) (2.05 g, 11.90 mmol) in dry DCM (40 ml) was added slowly. The reaction mixture was stirred for 2 h at 253 K, and then the suspension was poured into a mixture of aqueous NaHCO 3 solution (80 ml) and DCM (50 ml) and stirred at room temperature for 20 min. The organic phase was separated, and the aqueous phase was extracted with DCM (3 x 25 ml). The combined organic phase was washed with water and brine, and then dried over anhydrous MgSO 4 . After removal of the solvent in vacuo, the residue was chromatographed on silica gel to give the title compound as colorless crystals.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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.