Synthesis, crystal structure and Hirshfeld surface analysis of 1,7-dimethyl-5a,6,11a,12-tetrahydrobenzo[b]benzo[5,6][1,4]oxazino[2,3-e][1,4]oxazine

In the crystal, molecules are linked by pairs of C—H⋯O and N—H⋯C contacts into layers parallel to (100). H⋯H contacts make the largest contribution to the Hirshfeld surface (58.9%).


Chemical context
The title oxazine derivative contains two six-membered heterocyclic rings located between two benzene rings. Oxazine-derived compounds are used in the synthesis of detergents, corrosion inhibitors and industrial dyes (Adib et al., 2006). This class of molecules has been studied extensively as they exhibit antitumor (Sriharsha et al., 2006), antibacterial and antifungal (Belz et al., 2013) activity. Oxazinooxazines are important heterocyclic precursors in the construction of heteropropellanes with applications in material sciences and medicinal chemistry (Dilmaç et al., 2017). Such heterocycles can be synthesized by several methods (Konstantinova et al., 2020), with the most direct route being the condensation of amino alcohols with either aldehydes or ketones (Hajji et al., 2003). As the amino and hydroxy groups are adjacent, 2-aminophenol readily forms heterocycles. An interesting feature of the reaction is the stereo-selective transformation of glyoxal. We report herein the crystal structure and Hirshfeld surface analysis for a new oxazine derivative, 1,7-dimethyl-5a,6,11a,12-tetrahydrobenzo [b]

Structural commentary
The molecular structure of the title compound (I) is shown in Fig. 1. The molecules occupy special positions on the twofold ISSN 2056-9890 rotation axes. The heterocyclic ring adopts a slightly twisted envelope conformation with the C8* [symmetry code: (*) Àx À 1, y, Àz À 1 2 ] atom as the flap. Except for this atom, the symmetry-independent part of the molecule (C2-C8/O1/N1) is nearly planar, the largest separation from the mean plane being 0.1267 (10) Å for O1. The mean planes of the two halves of the molecule form a dihedral angle of 72.01 (2) .

Figure 2
Chains of the title molecules linked by pairs of C-HÁ Á ÁO interactions.     (2) , respectively] are smaller than in (I). In MOYJOC, both NH groups are involved in hydrogen bonds with the heterocyclic oxygen atoms. In FIGVOG, only one NH group takes part in such hydrogen bonding, while the other makes an N-HÁ Á ÁC contact similar to that observed in (I). In ABEQAA, the hydrogen atoms at the bridge C atoms (C8 and C8* in the title molecule) are replaced by methyl groups. As a result, the dihedral angle increases to 81.70 (2) . In this structure, both NH groups form weak intermolecular N-HÁ Á ÁO hydrogen bonds.

Synthesis and crystallization
To a solution of 2-amino-3-methylphenol ( The Hirshfeld surfaces of the title molecule mapped over (a) curvedness,

Figure 7
Two-dimensional fingerprint plot for the title molecule (a) and those delineated into the specific types of interactions (b-f).

Figure 5
View of the three-dimensional Hirshfeld surface for the title molecule plotted over d norm .
(20 ml) and the mixture was refluxed for 12 h. The orange product obtained was washed with ether and recrystallized from ethanol at room temperature (m.p. 472-475 K, yield 67%).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. All hydrogen atoms were constrained to ride on their parent atoms with C-H = 0.93, 0.96 and 0.98 Å for aromatic, methyl and methine H atoms, respectively, and with N-H = 0.86 Å . Isotropic displacement parameters of these atoms were constrained to 1.5U eq (C) for the methyl group and to 1.2U eq (C,N) for all other H atoms.  (Sheldrick, 2015b); molecular graphics: OLEX2 (Dolomanov et al., 2009) and Mercury (Macrae et al., 2020); software used to prepare material for publication: WinGX (Farrugia, 2012), SHELXL2018/3 (Sheldrick, 2015b), PLATON (Spek, 2020) and publCIF (Westrip, 2010).  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.15 e Å −3 Δρ min = −0.16 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.