The crystal structures and Hirshfeld surface analysis of 6-(naphthalen-1-yl)-6a-nitro-6,6a,6b,7,9,11a-hexahydrospiro[chromeno[3′,4′:3,4]pyrrolo[1,2-c]thiazole-11,11′-indeno[1,2-b]quinoxaline] and 6′-(naphthalen-1-yl)-6a′-nitro-6′,6a′,6b′,7′,8′,9′,10′,12a′-octahydro-2H-spiro[acenaphthylene-1,12′-chromeno[3,4-a]indolizin]-2-one

The crystal structures of the title spiro derivatives are described and the analysis of the intermolecular contacts in the crystals using Hirshfeld surface analysis and two-dimensional fingerprint plots is reported.

The stereochemistry, such as regioselectivity and enantioselectivity, of heterocyclic compounds (Huisgen, 1984) can be studied by 1,3-dipolar cycloaddition reactions. Against this background and considering the importance of their natural occurrence, biological, pharmacological and medicinal activities, use as synthetic intermediates, as well as in view of our ongoing research on the design of novel heterocycles, we have synthesized the title compounds and report herein their crystal structures.

Supramolecular features
For both compounds, the crystal structure is stabilized by intermolecular C-HÁ Á ÁO hydrogen bonds (Tables 1 and 2). In (I), the C-HÁ Á ÁO hydrogen bonds link adjacent molecules, forming R 2 2 (16) loops propagating along the b-axis direction. The loops are linked by C-HÁ Á ÁS hydrogen bonds, forming layers parallel to the (101) plane; C-HÁ Á Á interactions are present within the layers (Table 1, Fig. 3).
In the crystal of (II), molecules are linked by C-HÁ Á ÁO interactions, forming zigzag chains along the b-axis direction ( Fig. 4  View of the crystal packing of (II) along the a axis of the unit cell; only the H atoms involved in hydrogen bonding have been included.

Figure 2
The molecular structure of (II), with atom labelling. Displacement ellipsoids are drawn at the 30% probability level. The intramolecular C-HÁ Á ÁO hydrogen bond (Table 2) is shown as a dashed lines. Table 1 Hydrogen-bond geometry (Å , ) for (I).

Figure 3
View of the crystal packing of (I) along the a axis of the unit cell; only the H atoms involved in the weak interactions have been included. In this orientation, the atom O3 in position 1 À x, Ày, 1 À z is exactly superimposed on the O3 atom in position Àx, Ày, 1 À z, which interacts with C33-H33. The molecule in position Àx, Ày, 1 À z is not shown for clarity.
to form layers parallel to (100), yielding a three-dimensional supramolecular structure. No significantinteractions with centroid-centroid distances of less than 4 Å were observed in either compound.

Hirshfeld surface analysis
The Hirshfeld surface analysis (Spackman & Jayatilaka, 2009), and the associated two-dimensional fingerprint plots (McKinnon et al., 2007), employed to analyse the intermolecular contacts in the crystals, were performed with CrystalExplorer17 (Turner et al., 2017). The Hirshfeld surfaces of (I) and (II) mapped over d norm are given in Figs. 5 and 6, respectively, while the intermolecular contacts are illustrated in Fig. 7 for (I) and in Fig. 8 for (II). They are colour-mapped with the normalized contact distance, d norm , varying from red (distances shorter than the sum of the van der Waals radii) through white to blue (distances longer than the sum of the van der Waals radii). The red spots on the surface indicate the intermolecular contacts involved in hydrogen bonding.
The fingerprint plots for the two compounds are given in Figs The Hirshfeld surface mapped over d norm for (I) mapped over an arbitrary colour scale of À0.177 (red) to 3.260 (blue).

Figure 6
The Hirshfeld surface mapped over d norm for (II) mapped over an arbitrary colour scale of À0.080 (red) to 3.098 (blue).
The solutions were refluxed for 18 h in a Dean-Stark apparatus to give the cycloadducts. After completion of the reactions as indicated by TLC, the solvent was evaporated under reduced pressure. The crude products obtained were purified by column chromatography using hexane/EtOAc (7:3) as eluent (yield 84%). Colourless block-like crystals of the title compounds, suitable for X-ray diffraction analysis, were obtained by slow evaporation of solutions in ethanol.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. All H atoms were positioned geometrically, with N-H = 0.86 Å , C-H = 0.93-0.97 Å , and constrained to ride on their parent atoms with U iso (H) = 1.5U eq (C-methyl) and 1.2U eq (N, C) for all other H atoms.

6-(Naphthalen-1-yl)-6a-nitro
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.