Crystal structure and Hirshfeld surface analysis of 4,5-dibromo-2-(4-methoxyphenyl)-2,3,4,4a,5,6,7,7a-octahydro-1H-4,6-epoxy-1H-cyclopenta[c]pyridin-1-one

The title molecule comprises a fused tricyclic system containing two five-membered rings (cyclopentane and tetrahydrofuran) and one six-membered ring (tetrahydropyridinone). In the crystal, molecules are linked by intermolecular C—H⋯O hydrogen bonds and C—H⋯π, C—Br⋯π and C⋯O interactions into double layers.


Chemical context
Isoindoles are important structural units of many natural products and are widely used as drugs and as building blocks for the construction of new N-containing heterocyclic compounds or functional materials (Nadirova et al., 2019;Zubkov et al., 2011Zubkov et al., , 2014Zubkov et al., , 2018. The biological and physical properties of isoindoles depend on the attached functional groups (Krishna et al., 2021;Zaytsev et al., 2017Zaytsev et al., , 2019Zaytsev et al., , 2020. Thus, the functionalization of isoindole moieties at the donor/ acceptor sites for non-covalent bonding can improve their biological and photophysical properties as well as their coordination ability (Wicholas et al., 2006).

Structural commentary
As shown in Fig. 2, the molecule of the title compound, 2, comprises a fused tricyclic system containing two fivemembered rings (cyclopentane C4-C7/C7A and tetrahydrofuran C3A/C4-C6/O8) and one six-membered ring (tetrahydropyridinone C1/N2/C3/C3A/C4/C7A). Both fivemembered rings of the tricyclic fragment have envelope conformations with the C5 atom as the flap, and the sixmembered ring adopts a flattened chair conformation with the N2 and C4 atoms displaced by 0.276 (3) and À0.670 (4) Å , respectively, from the mean plane through the remaining four atoms. The environment of atom N2, being close to trigonalplanar, is slightly pyramidalized due to steric reasons [the sum of bond angles at N2 is 356.7 (5) ]. The dihedral angle between the mean planes of the tetrahydropyridinone and benzene rings is 82.82 (16) .

Figure 2
The molecular structure of 2, with displacement ellipsoids for nonhydrogen atoms drawn at the 30% probability level.

Figure 1
Synthesis of the title compound (2).
The racemic crystal of RUJJUC consists of enantiomeric pairs with the configurations rac-4R*,4aR*,5R*,6S*,7S*,7aR*. The ethanol solvate molecule is bound to the molecule of RUJJUC by a strong O-HÁ Á ÁO hydrogen bond. In the crystal of HUGJUP, there are three O-HÁ Á ÁO hydrogen bonds, which link the organic molecules and water molecules into layers parallel to (001). The layers are further linked into a three-dimensional framework by attractive intermolecular carbonyl-carbonyl interactions.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 4. All H atoms were positioned geometrically (C-H = 0.93 À 0.98 Å ) and refined using a riding model, with U iso (H) = 1.2U eq (C) or 1.5U eq (C-methyl).

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