Crystal structure and features of 3′,8-dibenzylidene-4a,5,6,7,8,8a-hexahydro-2′H-spiro[chromene-2,1′-cyclohexan]-2′-one

In the title compound, the C=C—C—C torsion angles in the phenylmethylidene units are 166.6 (3) and −48.0 (4)°. In the crystal, molecules form a three-dimensional network by means of weak C—H⋯O hydrogen bonds. The most important contributions to the crystal structure are the H⋯H interactions (68.8%).


Chemical context
Spiro heterocycles are of great interest for the creation of new promising biologically active compounds. The spiro center causes a rigid, spatially oriented configuration, which makes the compounds containing them potentially more complementary to binding sites for biological targets (Mirzabekova et al., 2008;Abou-Elmagd & Hashem, 2016;Saraswat et al., 2016). A convenient way obtain heterocyclic compounds, including those with the spiro chromane moiety, is dimerization of Mannich ketones (Shchekina et al., 2017).

Structural commentary
The structure of the title compound is shown in Fig. 1. The pyran, cyclohexanone and methylenecyclohexene units are each non-planar structures with the following puckering parameters: Q = 0.447 Å , = 128.1 , ' = 249.3 ; Q = 0.517 Å , = 167.2 , ' = 12.9 ; and Q = 0.460 Å , = 130.0 , ' = 39.9 , respectively. In the two phenylmethylidene moieties, the corresponding -bonds are shortened [C6-C7 = 1.475 (4) and C23-C22 = 1.471 (4) Å ], which allows us to speak of incompleteconjugation of aromatic rings and double bonds. These values are slightly longer than the bond lengths characteristic for complete conjugation in similarly constructed moieties (Golikov et al., 2006); in particular, for dibenzyl- ISSN 2056-9890 idenecyclohexanone it is 1.341 Å . The torsion angles C8 C7-C6-C5 and C18 C22-C23-C28 are similar [À38.5 (5) and À36.3 (5) , respectively], and reflect the noncoplanarity of the phenylmethylidene moiety, and therefore confirms incomplete conjugation of the phenyl and ylidene moieties (Kriven'ko et al., 2005). The values noted above significantly exceed the corresponding ones for torsion angles in analogous moieties in dibenzylidene cyclohexanones (À28.70 ; Jia et al., 1989). Such a significant deviation of the torsion angle from the expected value is probably due to van der Waals repulsion of hydrogen atoms on the cyclohexene atoms C9 and C19 and hydrogen atoms of the aromatic rings. Thus, the interatomic distance between the hydrogen atoms of the aromatic substituent at C5 and the methylene group at C9 is 2.27 Å , close to the sum of the van der Waals radii for research communications  Graphical representation of the hydrogen bonds (dashed lines) along the a axis.

Figure 3
Graphical representation of the hydrogen bonds (dashed lines) along the c axis.

Figure 1
The molecular structure of the title compound with atom-labeling scheme, with displacement ellipsoids drawn at the 50% probability level.

Figure 4
Graphical representation of the hydrogen bonds. hydrogen atoms (2.2 Å ). The C7 C8 bond is a little shorter than the C18 C22 bond [1.337 (4) and 1.346 (4) Å , respectively]. We believe that this is due to better conditions forconjugation of the Ph-C22 C18-C17 C16 unit compared to the Ph-C7 C8-C12 O1 unit. So, the value of the C22 C18-C17 C16 torsion angle is 166.6 (3) in comparison with 135.0 (3) for C7 C8-C12 O1, allowing us to conclude a more pronounced flat structure for the former unit. The O2-C17 bond is noticeably shorter [1.391 (3) Å ] than O2-C13 [1.446 (3) Å ] due to conjugation of the endocyclic oxygen atom and a multiple bond. The bond lengths of the spiro center are within expected values, and are typical of those in similar moieties (Clark et al., 2005;Kia et al., 2012).

Supramolecular features
In the crystal, the molecules are linked into a complex threedimensional network by means of weak C20-H20BÁ Á ÁO1 i and C11-H11BÁ Á ÁO1 i hydrogen bonds between (Figs. 2-4 and Table 1).

Analysis of the Hirshfeld Surfaces
The C11-H11BÁ Á ÁO1 i and C20-H20BÁ Á ÁO1 i interactions are visualized as bright-red spots between the corresponding donor and acceptor atoms on the Hirshfeld surfaces, mapped by d norm (Fig. 5). This is confirmed by the Hirshfeld surfaces, displayed as the electrostatic potential (Fig. 6), showing a negative potential around the oxygen atoms in the form of light-red clouds and a positive potential around the H atoms in the form of bluish clouds. The HÁ Á ÁO contacts account for about 4.5% of the Hirshfeld surface displayed on the fingerprint plots with a curved surface with d e + d i $2.2 Å (Fig. 7). The largest proportion, 68.8%, is for HÁ Á ÁH contacts, with a bright splash on the fingerprint plot corresponding to d e + d i $2.2 Å . The CÁ Á ÁH interaction corresponds to 12.2% d e + d i $2.4 Å with peaks in the region of the aromatic rings ( Fig. 7). The presence ofstacking reflects the presence of CÁ Á ÁC contacts, which account for only 1.0% of the Hirschfield surface with d e + d i $2.2 Å .  Table 1 Hydrogen-bond geometry (Å , ).

Figure 5
Graphical representation of the Hirshfeld surface mapped over d norm .
The highlighted red spots on the top face of the surfaces indicate contact points with the atoms participating in the C-HÁ Á ÁO intermolecular interactions.

Figure 6
Graphical representation of the electrostatic potential surfaces.

Figure 7
Graphical representation of the Hirshfeld surface two-dimensional fingerprint plot for the title compound (a) showing the:

Database survey
The structure and configuration of the molecule is complex and includes a spiro node and arylmethylidene moieties. A similar spiro ring based on the Mannich ketone was described earlier (Siaka et al., 2012). The tetrahydropyridine ring is in an unsymmetrical half-chair conformation, while the cyclohexadiene and cyclohexene rings display semi-boat conformations.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2.

3′,8-Dibenzylidene-4a,5,6,7,8,8a-hexahydro-2′H-spiro[chromene-2,1′-cyclohexan]-2′-one
Crystal data Special details Geometry. All s.u.'s (except the s.u.in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'s involving l.s. planes.