3-Cyclopentylsulfonyl-5-fluoro-2-methyl-1-benzofuran

There are two independent molecules, A and B, in the asymmetric unit of the title compound, C14H15FO3S, in each of which the cyclopentyl ring adopts an envelope conformation. The benzofuran units in each molecule are essentially planar, with mean deviations from the least-squares plane defined by the nine constituent ring atoms of 0.009 (2) Å for molecule A and 0.013 (2) Å for molecule B. In the crystal, molecules are linked by weak C—H⋯O hydrogen bonds. In the cyclopentyl ring of molecule B, one C atom is disordered over two positions with site-occupancy factors of 0.60 (2) and 0.40 (2).

& B] in which the benzofuran unit is essentially planar, with a mean deviation of 0.009 (2) Å for A and 0.013 (2) Å for B, respectively, from the least-squares plane defined by the nine constituent atoms. The cyclopentyl rings of both molecules are in an envelope form. In the cyclopentyl ring of molecule B, C27 atom is disordered over two positions with site-occupancy factors, from refinement of 0.60 (2) (part 1) and 0.40 (8) (part 2). In the crystal packing (Fig. 2), molecules are linked by weak non-classical intermolecular C-H···O hydrogen bonds; the first one between a methyl H atom and the O atom of the sulfonyl group (Table 1; C9-H9C···O6 i ), the second one between a benzene H atom and the O atom of the sulfonyl group (Table 1; C19-H19···O6 ii ), and the third one between a methyl H atom and the O atom of the sulfonyl group (Table 1; C23-H23A···O2 iii ).
Experimental 3-chloroperoxybenzoic acid (77%, 560 mg, 2.5 mmol) was added in small portions to a stirred solution of 3-cyclopentylsulfanyl-5-fluoro-2-methyl-1-benzofuran (325 mg, 1.2 mmol) in dichloromethane (40 mL) at 273 K. After being stirred at room temperature for 8h, 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 (hexane-ethyl acetate, 4:1 v/v) to afford the title compound as a colorless solid [yield 71%, m.p. 394-395 K; R f = 0.49 (hexane-ethyl acetate, 4:1 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 = 0.95 Å for aryl, 1.00 Å for methine, 0.99 Å for methylene and 0.98 Å for methyl H atoms, respectively. U iso (H) = 1.2U eq (C) for aryl, methine, methylene, and 1.5U eq (C) for methyl H atoms. The C27 atom of the cyclopentyl ring is disordered over two positions with site-ccupancy factors, from refinement of 0.60 (2) (part A) and 0.40 (2) (part B). The C-C distance sets were restrained to be with 0.003 Å using command DFIX and SADI, and thermal ellipsoid parameters of C27A and C27B set were restrained to 0.01 using commend ISOR.  Fig. 1. The molecular structure of the title compound with the atom numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. H atoms are presented as a small spheres of arbitrary radius.

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.