Crystal structure and Hirshfeld surface analysis of ethyl 6′-amino-2′-(chloromethyl)-5′-cyano-2-oxo-1,2-dihydrospiro[indoline-3,4′-pyran]-3′-carboxylate

The molecules are connected in the crystal by N—H⋯O hydrogen-bond pairs along the b-axis direction as dimers with (8) and (14) ring motifs and as ribbons by intermolecular C—H⋯N hydrogen bonds. Between the ribbons, there are weak van der Waals contacts.


Chemical context
Being the most significant tools in organic synthesis, carboncarbon and carbon-heteroatom coupling reactions are important for the construction of fine chemicals such as pharmaceuticals, fragrances, antioxidants, etc. (Yadigarov et al., 2009;Khalilov et al., 2018a,b;Zubkov et al., 2018). These methods have found widespread application in the design of diverse heterocyclic ring systems, as well as spiro-heterocyclic compounds Maharramov et al., 2019;Mahmoudi et al., 2019;Mamedov et al., 2019;Yin et al., 2020). The spirooxindole moiety is a key bioactive fragment of various natural products (Fig. 1), series of derivatives already being used in medicinal practice (Zhou et al., 2020).

Figure 1
Natural products containing the spirooxindole motif.

Figure 3
A view of the intermolecular N-HÁ Á ÁO and C-HÁ Á ÁN hydrogen bonds in the crystal packing of the title compound down the a axis.

Hirshfeld surface analysis
A Hirshfeld surface analysis was performed to investigate the intermolecular interactions (Tables 1 and 2) quantitatively and the associated two-dimensional fingerprint plots (McKinnon et al., 2007) were generated with CrystalExplorer17 (Turner et al., 2017). The Hirshfeld surface plotted over d norm in the range À0.6053 to 1.4079 a.u. is shown in Fig. 5. The red spots on the Hirshfeld surface represent N-HÁ Á ÁO contacts. The Hirshfeld surface mapped over electrostatic potential (Spackman et al., 2008) is shown in Fig. 6. The positive electrostatic potential (blue region) over the surface indicates hydrogen-donor potential, whereas the hydrogen-bond acceptors are represented by negative electrostatic potential (red region). Fig. 7 shows the full two-dimensional fingerprint plot and those delineated into the major contacts: the HÁ Á ÁH (34.9%;  Table 2 Summary of short interatomic contacts (Å ) in the title compound.

Figure 4
A view of the intermolecular N-HÁ Á ÁO and C-HÁ Á ÁN hydrogen bonds in the crystal packing of the title compound down the b axis.

Figure 6
View of the three-dimensional Hirshfeld surface of the title compound plotted over electrostatic potential energy in the range À0.0500 to 0.0500 a.u. using the STO-3 G basis set at the Hartree-Fock level of theory. Hydrogen-bond donors and acceptors are shown as blue and red regions around the atoms, corresponding to positive and negative potentials, respectively.
In the crystal of HIRNUS, the six-membered pyran ring adopts a near-boat conformation. The crystal structure features two intramolecular C-HÁ Á ÁO interactions and the crystal packing is stabilized by intermolecular N-HÁ Á ÁO hydrogen bonds. These lead to two primary motifs, viz. R 2 2 (12) and C(8). Combination of these primary motifs leads to a secondary R 2 2 (20) ring motif. In the crystal of JEGWEX, a potential precursor for fluoroquinoline synthesis, the pyran ring is nearly planar, with the most outlying atoms displaced from the best-plane fit through all non-H atoms by 0.163 (2) and 0.118 (2) Å . The molecules are arranged in layers oriented parallel to the (011) plane. In addition, the molecules are linked by a weak C-HÁ Á ÁO hydrogen bond, which gives rise to chains with base vector [111].
In WIMBEC, the pyran ring exhibits a near-boat conformation with puckering parameters Q T = 0.085 (7) Å , = 84 (5) and ' = 154 (5) . In the crystal, molecules are linked as dimers by pairs of N-HÁ Á ÁO hydrogen bonds, forming ribbons along the b-axis direction. These ribbons are connected by weak van der Waals interactions, stabilizing the molecular packing.

Synthesis and crystallization
The title compound was synthesized using previously reported procedures (Luo et al., 2015;Magerramov et al., 2018), and colourless needles were obtained upon recrystallization from methanol solution.

Refinement details
Crystal data, data collection and structure refinement details are summarized in Table 3. The H atoms of the NH and NH 2 groups were located in a difference map, and their positional parameters were allowed to freely refine [N1-H1 = 0.853 (17), N2-H2A = 0.843 (19) and N2-H2B = 0.889 (18) Å ], but their isotropic displacement parameters were constrained to take a value of 1.2U eq (N). All H atoms bound to C atoms were positioned geometrically and refined as riding with C-H = 0.95 (aromatic), 0.99 (methylene) and 0.98 Å (methyl), with U iso (H) = 1.5U eq (C) for methyl H atoms and 1.2U eq (C) for the others. Four reflections, 0 0 1, 0 1 0, 1 0 0 and 1 2 0, affected by the incident beam-stop and owing to poor agreement between observed and calculated intensities, and five outliers, 1 3 3, 3 1 1, 1 1 4, 1 6 9 and 4 11 2, were omitted in the final cycles of refinement.

Ethyl 6′-amino-2′-(chloromethyl)-5′-cyano-2-oxo-1,2-dihydrospiro[indoline-3,4′-pyran]-3′-carboxylate
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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq