3-(4-Chlorophenylsulfinyl)-2,4,6-trimethyl-1-benzofuran

In the title molecule, C17H15ClO2S, the 4-chlorophenyl ring is oriented approximately perpendicular to the mean plane of the benzofuran ring [dihedral angle = 88.98 (4)°]. In the crystal, molecules are linked through weak intermolecular C—H⋯O and C—H⋯π interactions, forming right-hand pseudo-helices along the a axis.


Comment
Many compounds involving a benzofuran ring system exhibit important pharmacological properties such as antifungal, antimicrobial, antitumor and antiviral activities (Aslam et al., 2006;Galal et al., 2009;Khan et al., 2005). These compounds widely occur in nature (Akgul & Anil, 2003;Soekamto et al., 2003). As a part of our study of the substituent effect on the solid state structures of 3-(4-chlorophenylsulfinyl)-2-methyl-1-benzofuran analogues (Choi et al., 2010a,b), we report herein the crystal structure of the title compound.
In the title molecule ( Fig. 1), the benzofuran unit is essentially planar, with a mean deviation of 0.009 (2) Å from the least-squares plane defined by the nine constituent atoms. The 4-chlorophenyl ring makes a dihedral angle of 88.98 (4)°w ith the mean plane of the benzofuran fragment. The crystal packing (Fig. 2) is stabilized by a weak intermolecular C-H···O hydrogen bond between the 4-chlorophenyl H atom and the oxygen of the S═O unit (C13-H13···O2 i ; Table 1), and by an intermolecular C-H···π interaction between a methyl H atom and the 4-chlorophenyl ring (C11-H11C···Cg ii ; Table 1, Cg is the centroid of the C12-C17 4-chlorophenyl ring).
The title compound is crystallized in the non-centrosymmetric space group Pna2 1 in spite of having no asymmetric C atoms. The space group is caused by a right hand pseudo-helix along the a axis (Fig. 2).
Experimental 3-Chloroperoxybenzoic acid (77%, 291 mg, 1.3 mmol) was added in small portions to a stirred solution of 3-(4-chlorophenylsulfanyl)-2,4,6-trimethyl-1-benzofuran (363 mg, 1.2 mmol) in dichloromethane (30 mL) at 273 K. After being stirred at room temperature for 3h, the mixture was washed with saturated sodium bicarbonate solution and the organic layer was separated, dried over magnesium sulfate, filtered and concentrated at reduced pressure. The residue was purified by column chromatography (silica gel, hexane-ethyl acetate, 2:1 v/v) to afford the title compound as a colorless solid [yield 83%, m.p. 452-453 K; R f = 0.62 (hexane-ethyl acetate, 2:1 v/v)]. Single crystals suitable for X-ray diffraction were prepared by slow evaporation of a solution of the title compound in ethyl acetate at room temperature.

Refinement
All H atoms were positioned geometrically and refined using a riding model, with C-H = 0.93 Å for aryl and 0.96 Å for methyl H atoms. U iso (H) = 1.2U eq (C) for aryl and 1.5U eq (C) for methyl H atoms.

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.