2-(5-Fluoro-3-isopropylsulfanyl-1-benzofuran-2-yl)acetic acid

The title compound, C13H13FO3S, was prepared by alkaline hydrolysis of ethyl 2-(5-fluoro-3-isopropylsulfanyl-1-benzofuran-2-yl)acetate. In the crystal, the carboxy groups are involved in intermolecular O—H⋯O hydrogen bonds, which link the molecules into centrosymmetric dimers. These dimers are further packed into stacks along the b axis by a slipped π–π interaction between the furan and benzene rings of neighbouring molecules [centroid–centroid distance = 3.727 (2) Å, interplanar distance = 3.465 (2) Å and slippage = 1.373 (2) Å]. The crystal structure also exhibits a short S⋯O contact [S⋯O = 3.219 (2) Å].

In the title molecule ( Fig. 1), the benzofuran unit is essentially planar, with a mean deviation of 0.014 (2) Å from the least-squares plane defined by the nine constituent atoms. In the crystal structure, the carboxyl groups are involved in intermolecular O-H···O hydrogen bonds (Table 1 & Fig. 2), which link the molecules into centrosymmetric dimers. These dimers are further packed into stacks along the b axis by a weak slipped π-π interaction between the furan and benzene rings of neighbouring molecules, with a Cg1···Cg2 iii distance of 3.727 (2) Å and an interplanar distance of 3.465 (2) Å resulting in a slippage of 1.373 (2) Å (Cg1 and Cg2 are the centroids of the C1/C2/C7/O1/C8 furan ring and the C2-C7 benzene ring, respectively). The crystal packing (Fig. 2) is further stabilized by an intermolecular S···O contact between the S atom and the O atom of the hydroxyl group [S1···O2 ii = 3.219 (2) Å].

Experimental
Ethyl 2-(5-fluoro-3-isopropylsulfanyl-1-benzofuran-2-yl)acetate (355 mg, 1.2 mmol) was added to a solution of potassium hydroxide (337 mg. 6 mmol) in water (10 ml) and methanol (10 ml), and the mixture was refluxed for 5 h, then cooled. Water (10 ml) was added, and the solution was extracted with dichloromethane. The aqueous layer was acidified to pH 1 with concentrated hydrochloric acid and then extracted with chloroform, dried over magnesium sulfate, filtered and concentrated at reduced pressure. The residue was purified by column chromatography (ethyl acetate) to afford the title compound as a colorless solid [yield 89%, m.p. 399-400 K; R f = 0.58 (ethyl acetate)]. Single crystals suitable for X-ray diffraction were prepared by slow evaporation of a solution of the title compound in diisopropyl ether at room temperature.

Refinement
Atom H2 of the hydroxy group was found in a different Fourier map and refined freely. The other H atoms were positioned geometrically and refined using a riding model, with C-H = 0.93 Å for the aryl, 0.98 Å for the methine, 0.97 Å for the methylene, and 0.96 Å for the methyl H atoms. U iso (H) =1.2U eq (C) for the aryl, methine, and methylene H atoms, and 1.5U eq (C) for the methyl H atoms.
supplementary materials sup-2 Figures   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 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.