3-(4-Fluorophenylsulfinyl)-2,4,6,7-tetramethyl-1-benzofuran

In the title compound, C18H17FO2S, the 4-fluorophenyl ring is almost perpendicular to the benzofuran fragment [88.07 (5)°]. The crystal structure exhibits weak intermolecular C—H⋯O hydrogen bonds and C—H⋯π interactions. The molecules form pseudo-helices along the a axis.

In the title compound, C 18 H 17 FO 2 S, the 4-fluorophenyl ring is almost perpendicular to the benzofuran fragment [88.07 (5) ]. The crystal structure exhibits weak intermolecular C-HÁ Á ÁO hydrogen bonds and C-HÁ Á Á interactions. The molecules form pseudo-helices along the a axis.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: GW2077).
The benzofuran unit is essentially planar, with a mean deviation of 0.008 (2) Å from the least-squares plane defined by the nine constituent atoms. The 4-fluorophenyl ring is almost perpendicular to the plane of the benzofuran fragment [88.07 (5)°] and is tilted slightly towards it. The crystal packing (Fig. 2) is stabilized by two intermolecular C-H···O hydrogen bonds; the first between the 4-fluorophenyl H atom and the furan O atom, with a C15-H15···O1 i , and the second between the 4-fluorophenyl H atom and the oxygen of the S═O unit, with a C18-H18···O2 ii , respectively (Table 1).
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.3).
The molecular packing (Fig. 3) is further stabilized by two intermolecular C-H···π interactions; the first between the methyl H atom and the 4-fluorophenyl ring, with a C11-H11A···Cg ii , the second between the methyl H atom and 4-fluorophenyl ring of an adjacent molecule, with a C12-H12A···Cg iii , respectively (Table 1; Cg is the centroid of the C13-C18 4-fluorophenyl ring.) Experimental 77% 3-Chloroperoxybenzoic acid (291 mg, 1.3 mmol) was added in small portions to a stirred solution of 3-(4-fluorophenylsulfanyl)-2,4,6,7-tetramethyl-1-benzofuran (360 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 in vacuum. The residue was purified by column chromatography (hexane-ethyl acetate, 1:1 v/v) to afford the title compound as a colorless solid [yield 82%, m.p. 437-438 K; R f = 0.53 (hexane-ethyl acetate, 1:1 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.

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.