Crystal structures and conformations of two Diels–Alder adduct derivatives: 1,8-bis(thiophen-2-yl)-14-oxatetracyclo[6.5.1.02,7.09,13]tetradeca-2(7),3,5-trien-10-one and 1,8-diphenyl-14-oxatetracyclo[6.5.1.02,7.09,13] tetradeca-2,4,6-trien-10-one

The title compounds are the product of a tandem ‘pincer’ Diels–Alder reaction consisting of [2 + 2] cycloadditions between benzo[c]furan and cyclopentanone. The molecules are linked via weak C—H⋯O intermolecular hydrogen bonds, which generate (16) ring motifs in compound (I) and C(8) chains in compound (II). In both structures, the crystal packing also features C—H⋯π interactions.


Chemical Context
The tandem 'pincer' Diels-Alder reaction, consisting of two consecutive [2 + 2] cycloadditions between two dienes and an acetylenic bis-dienophile, when furan derivatives are used as the diene components (Lautens & Fillion, 1997). The Diels-Alder reaction is among the most powerful C-C-bondforming processes and one of the most widely used and studied transformations in organic chemistry (Denmark & Thorarensen, 1996). Thiophene derivatives are very important heterocyclic compounds, which possess antitubercular (Parai et al., 2008), anti-depressant (Wardakhan et al., 2008), antiinflammatory (Kumar et al., 2004), anti-HIV (Bonini et al., 2005) and anti-breast cancer activities (Brault et al., 2005). Against this background, the conformational studies and X-ray structure determination of the title compounds have been carried out and the results are presented here. ISSN 2056-9890

Structural Commentary
The molecular structures of (I) and (II) are shown in Figs. 1 and 2, respectively, along with the atomic as well as ringlabelling schemes. Both compounds exhibit disorder, viz., in the thiophene rings of (I) and the oxygen atom of the cyclopentanone ring in (II). Further details are given in the Refinement section.

Figure 2
The molecular structure of compound (II) with the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. Table 1 Hydrogen-bond geometry (Å , ) for (I).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. Compound (I) initially refined to a high R index of 0.103 (2) and the difference Fourier map showed relatively larger peaks [Á max = 0.97 (2) e Å À3 ]. A preliminary check with TWINLAW (Bolte, 2004) showed that the crystal had twofold twinning by non-merohedry about [001] with a twin matrix of [À1 00 À0.101 1 À0.484 0 0 À1]. The twin law operated from the F o -F c table was used to a generate an HKLF5 format file (Bolte, 2004) suitable for twin refinement in SHELXL97 (Sheldrick, 2015). The twinning was a twofold rotation axis parallel to the b axis with a refined twin scale factor of 0.275 (2). The structure was refined to an improved R index of 0.064 (2)   The crystal packing of compound (I), viewed down the a axis, showing the C20-H20Á Á ÁO2 i intermolecular hydrogen bond (dashed lines), which results in R 2 2 (16) ring motifs. Hydrogen atoms not involved in this hydrogen bond are excluded for clarity. [Symmetry code: (i) 1 À x, Ày, 1 À z.]

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > σ(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.