Crystal structure and Hirshfeld surface analysis of 4,5-dibromo-6-methyl-2-phenyl-2,3,3a,4,5,6,7,7a-octahydro-3a,6-epoxy-1H-isoindol-1-one

In the crystal, molecules are linked into dimers by pairs of C—H⋯O hydrogen bonds, thus generating (18) rings. The crystal packing of the title compound is dominated by H⋯H, Br⋯H, H⋯π and Br⋯π interactions.


Chemical context
The halogenation of oxabicycloheptenes plays an important role in the chemical transformations of bridged heterocycles because of the ability to carry out a complex transformation of the carbon skeleton in one step, which makes it possible to obtain products that are practically inaccessible in other ways from relatively simple starting compounds. The halogenation reaction of oxabicycloheptenes coupled with carbon-or nitrogen-containing rings, with the help of various halogenating agents, proceeds in two possible general directions, depending on the nature of the halogenating agent and the structure of the substrate. Analysis of the literature data does not allow one to reliably predict the direction of the halogenation of oxabicycloheptenes. It can on the one hand be the halogen-initiated Wagner-Meerwein cationic rearrangement (Jung et al., 1985;Ciganek et al., 1995;Zubkov et al., 2004Zubkov et al., , 2018Zaytsev et al., 2020), or on the other hand we can observe electrophilic addition of halogens to multiple bonds (Berson et al., 1954;Barlow et al., 1971;Kobayashi et al., 1976;Solov'eva et al., 1984). Halogenated organic compounds are of interest because of their photoactivity in the solid state, high solubility in halocarbons, high thermal and oxidative stability, etc., to which non-covalent halogen bonding can contribute (Afkhami et al., 2017;Maharramov et al., 2018;Mahmoudi et al., 2017Mahmoudi et al., , 2019Shixaliyev et al., 2014). In view of its higher directionality, the halogen bond can be better suited than the hydrogen bond for the building of functional materials by non-covalent self-assembly via specific molecular interactions Kopylovich et al., 2011;Ma et al., 2017aMa et al., ,b, 2020Mahmudov et al., 2012Mahmudov et al., , 2013Mahmudov et al., , 2019Mahmudov et al., , 2020. In a previous work , the formation of a halogenated Wagner-Meervein rearrangement product under the action of molecular bromine in dry dichloromethane on isoindole 1 was shown. In this study, the effect of [(Me 2 NCOMe) 2 H] + Br 3 À (Rodygin et al., 1992;Prokop'eva et al., 2008) is reported. The different course of the halogenation reaction was shown to be anti-addition on the double bond with the formation of the title compound, 4,5-dibromo-6-methyl-2-phenylhexahydro-3a,6-epoxy-isoindol-1(4H)-one, 2 ( Fig. 1).

Supramolecular features
The crystal packing of the title compound is consolidated by C-HÁ Á ÁO hydrogen bonds (Table 1, Fig. 3) and C-HÁ Á Á and C-BrÁ Á Á interactions (Table 1, Fig. 4). In the crystal, pairs of C-HÁ Á ÁO hydrogen bonds link molecules into dimers with R 2 2 (18) ring motifs (Bernstein et al. 1995 The molecular structure of the title compound with displacement ellipsoids for the non-hydrogen atoms drawn at the 30% probability level. The atoms Br2 and Br2A represent the major and minor components of the disorder, respectively. Table 1 Hydrogen-bond geometry (Å , ).

Figure 3
A view of the intermolecular C-HÁ Á ÁO interactions in the crystal structure of the title compound. Only the major component of the disorder is shown.

Hirshfeld surface analysis
In order to present the intermolecular interactions in the crystal structure of the title compound in a visual manner, Hirshfeld surfaces (McKinnon et al., 2007) and their associated two-dimensional fingerprint plots (Spackman & McKinnon, 2002) were generated using CrystalExplorer17 (Turner et al., 2017). The Hirshfeld surface plotted over d norm in the range À0.1151 to 1.1998 a.u. is shown in Fig. 5

Figure 4
A view of the intermolecular C-HÁ Á Á and C-BrÁ Á Á interactions in the crystal structure of the title compound. Only the major component of the disorder is shown.

Database survey
In the crystal of ERIVIL, weak intermolecular C-HÁ Á ÁO hydrogen bonds link the molecules into R 2 2 (8) and R 2 2 (14) rings, thus forming the chains along the b-axis direction. In the crystal of AGONUH, C-HÁ Á ÁO hydrogen bonds link the molecules into zigzag chains running along the b-axis direction. In TIJMIK, two types of C-HÁ Á ÁO hydrogen bonds generate R 2 2 (20) and R 4 4 (26) rings, with adjacent rings running parallel to the ac plane. Further C-HÁ Á ÁO hydrogen bonds form a C(6) chain, linking the molecules in the b-axis direction. In UPAQEI, molecules are linked by C-HÁ Á ÁO hydrogen bonds. In YAXCIL, C-HÁ Á ÁO hydrogen bonds link the molecules into a three-dimensional network. In MIGTIG, the molecules are linked only by weak van der Waals interactions.

Synthesis and crystallization
The solution of isoindolone 1 (4 mmol) and the brominating agent (4 mmol) in 15 mL of dry chloroform was heated under reflux for 20 h (TLC control, EtOAc-hexane, 1:1). The reaction mixture was poured into H 2 O (50 mL) and extracted with CHCl 3 (3 Â 20 mL). The combined organic fractions were dried over anhydrous Na 2 SO 4 , the solvent was evaporated under reduced pressure, and the solid residue was recrystallized from a hexane-AcOEt

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 4. All the C-bound H atoms were positioned geometrically, with C-H = 0.93 Å (for aromatic H atoms), 0.98 Å (for methine H atoms), 0.97 Å (for methylene H atoms) and 0.96 Å (for methyl H atoms), and constrained to ride on their parent atoms, with U iso (H) = 1.2U eq (C) [1.5U eq (C) for methyl H atoms]. The Br2 atom attached to the atom C2 is disordered over two sites, with occupancies of 0.833 (8)/0.167 (8). The two components of the disorder (Br2 and Br2A) were refined with restraints so that their bond lengths are comparable. Owing to poor agreement, five reflections, i.e. (126), (204), (115), (321) and (006), were omitted from the final cycles of refinement.

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.