Two closely related 2-(benzofuran-2-yl)-2-oxoethyl benzoates: structural differences and C—H⋯O hydrogen-bonded supramolecular assemblies

The title compounds contain a benzofuran ring and an ortho-substituted phenyl ring connected by a carbonyl bridge. The molecular conformations of both compounds are similar, but differ in the torsion angles between the ortho-substituted phenyl ring and its adjacent carbonyl group. The crystal structures feature C—H⋯O hydrogen bonds.

The compounds 2-(1-benzofuran-2-yl)-2-oxoethyl 2-nitrobenzoate, C 17 H 11 NO 6 (I), and 2-(1-benzofuran-2-yl)-2-oxoethyl 2-aminobenzoate, C 17 H 13 NO 4 (II), were synthesized under mild conditions. Their molecular structures were characterized by both spectroscopic and single-crystal X-ray diffraction analysis. The molecular conformations of both title compounds are generally similar. However, different ortho-substituted moieties at the phenyl ring of the two compounds cause deviations in the torsion angles between the carbonyl group and the attached phenyl ring. In compound (I), the ortho-nitrophenyl ring is twisted away from the adjacent carbonyl group whereas in compound (II), the ortho-aminophenyl ring is almost co-planar with the carbonyl group. In the crystal of compound (I), two C-HÁ Á ÁO hydrogen bonds link the molecules into chains propagating along the c-axis direction and the chains are interdigitated, forming sheets parallel to [201]. Conversely, pairs of N-HÁ Á ÁO hydrogen bonds in compound (II) link inversion-related molecules into dimers, which are further extended by C-HÁ Á ÁO hydrogen bonds into dimer chains. These chains are interconnected byinteractions involving the furan rings, forming sheets parallel to the ac plane.

Chemical context
Oxygen-containing heterocycles are the basic cores of many bioactive structures. Among these, benzofuran and its derivatives occur frequently in nature because of their stability and ease of generation. Those with substitution(s) at their C-2 and/or C-3 positions are important. Important biological activity such as anticancer (Swamy et al., 2015), anti-acetylcholinesterase (Zhou et al., 2010), antimicrobial (Ugale et al., 2012) and antioxidant (Naik et al., 2013) actions exhibited by this scaffold have attracted the attention of synthetic chemists. Some of the biological and medicinal significance of benzofuran derivatives (Nevagi et al., 2015) have been discussed in review reports. The known potential of benzofuran derivatives has motivated us to synthesise some new compounds incorporating this core structure and we herein report the synthesis and crystal structures of 2-(1-benzofuran-2-yl)-2-oxoethyl 2nitrobenzoate (I) and 2-(1-benzofuran-2-yl)-2-oxoethyl 2aminobenzoate (II).

Database survey
A survey of the Cambridge Structural Database (Groom et al., 2016) revealed five benzofuran structures (Kumar et al., 2015) similar to the title compounds: ITAXUY, ITAYAF, ITAYEJ, ITAYIN and ITAYOT. The molecular structures of the studied and previous compounds differ only at their substituted phenyl rings. By comparing their torsion angles at the        Interactions in the crystal structure of compound (II), showing hydrogen bonds (cyan dotted lines) and Á Á Á interactions (red dotted lines).

Synthesis and crystallization
The synthesis was carried out by reacting 1-(benzofuran-2-yl)-2-bromoethan-1-one (1 mmol) with 2-nitrobenzoic acid (1 mmol) for compound (I) and 2-aminobenzoic acid (1 mmol) for compound (II) in 8 ml of N,N-dimethylformamide in the presence of a catalytic amount of anhydrous potassium carbonate at room temperature. The reaction solution was stirred for about two h and monitored by thinlayer chromatography (TLC). After the reaction was complete, the resultant mixture was then added to a beaker of ice-cooled water to form a precipitate. The precipitate was then filtered, rinsed with distilled water and dried. Crystals suitable for X-ray analysis were obtained by slow evaporation using a suitable solvent.

(I) 2-(1H-1-Benzofuran-2-yl)-2-oxoethyl 2-nitrobenzoate
Crystal data where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.18 e Å −3 Δρ min = −0.17 e Å −3 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq N1 0.5075 (2) 0.27391 (8) Hydrogen 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.