Steric repulsion and supramolecular assemblies via a two-dimensional plate by C—H⋯O hydrogen bonds in two closely related 2-(benzofuran-2-yl)-2-oxoethyl benzoates

The title compounds are constructed from a benzofuran ring and an ortho-substituted phenyl ring connected by a carbonyl-connecting bridge. The structural conformation of the compounds are under substantial influence of steric repulsion. In the crystals, the molecules are connected by C—H⋯O hydrogen bonds and π–π interactions [with extra C—H⋯π interaction for compound (II)].


Chemical context
Benzofurans are an important class of heterocyclic compounds with fused benzene and furan rings. The benzofuran nucleus has been widely used as the building block for various biologically active compounds due to its broad range of pharmacological properties (Swamy et al., 2015;Zhou et al., 2010;Rangaswamy et al., 2012). Benzofuran derivatives, especially with substituents at their C-2 position, are commonly found in natural products and synthetic compounds. Several reviews describing the biological potential of these scaffolds acting as antioxidant (Chand et al., 2017), antimicrobial (Hiremathad et al., 2015), anticancer and antiviral (Khanam & Shamsuzzaman, 2015) agents have been published. Encouraged by previous studies, we are herein reporting the synthesis, spectroscopic studies and structure determination of 2-(benzofuran-2-yl)-2-oxoethyl 2-chlorobenzoate (I) and 2-(benzofuran-2-yl)-2-oxoethyl 2-methoxybenzoate (II).

Figure 1
The structures of (I) and (II), showing 50% probability displacement ellipsoids and the atomic labelling scheme.

Figure 4
The crystal packing of compound (I), showing hydrogen bonds (cyan dotted lines) andinteractions (red dotted lines).

Figure 5
Intermolecular hydrogen bonds joining molecules into an endless chain in compound (II).

Figure 6
Intermolecular interactions in compound (II), showing the two-dimensional plate parallel to the ac plane.

Database survey
A search of the Cambridge Structural Database (Groom et al., 2016) by using 2-(1-benzofuran-2-yl)-2-oxoethyl benzoate as reference skeleton has revealed five benzofuran structures (Kumar et al., 2015) related to the title compounds, i.e. ITAXUY, ITAYAF, ITAYEJ, ITAYIN and ITAYOT. The molecular structures of these compounds differ only at their substituted phenyl rings, especially compound (I) with ITAYAF and compound (II) with ITAYIN, which have the same substituents at altered positions. By looking at their torsion angles at the C-C( O)-O-C( O) carbonyl connecting bridge, compound (I) was found to exhibit a synclinal conformation similar to ITAXUY, ITAYEJ and ITAYIN (2 ranges from 75 to 80 ) whereas compound (II) shows an anti-periplanar conformation as do ITAYAF and ITAYOT (ranging from 163 to 180 ).

Synthesis and crystallization
The title compounds were synthesized by dissolving a mixture of 1-(benzofuran-2-yl)-2-bromoethan-1-one (1 mmol) with 2-chlorobenzoic acid (1 mmol) for compound (I) and 2-methoxybenzoic acid (1 mmol) for compound (II) in N,Ndimethylformamide (8 ml). The solution was stirred for about two h at room temperature in the presence of a catalytic amount of anhydrous potassium carbonate and the progress was monitored by thin-layer chromatography (TLC). Once the reaction was complete, the resultant mixture was poured into a beaker of ice cooled water which gave a precipitate. The precipitate obtained was then filtered, washed with distilled water and dried. Finally, pure crystals suitable for X-ray analysis were obtained by slow evaporation using a suitable solvent.
Program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015) for (I); SHELXL2013 (Sheldrick, 2015) for (II). For both structures, molecular graphics: SHELXL2013 (Sheldrick, 2015) and Mercury (Macrae et al., 2006); software used to prepare material for publication: SHELXL2013 (Sheldrick, 2015) and PLATON (Spek, 2009). 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.

2-(Benzofuran-2-yl)-2-oxoethyl 2-methoxybenzoate (II)
Crystal data 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.  (9) Hydrogen-bond geometry (Å, º) Cg3 is the centroid of the C12-C17 ring. π-π interactions in compound (II).