Crystal structure of (1S,2S,2′R,3a′S,5R)-2′-[(5-bromo-1H-indol-3-yl)methyl]-2-isopropyl-5,5′-dimethyldihydro-2′H-spiro[cyclohexane-1,6′-imidazo[1,5-b]isoxazol]-4′(5′H)-one

The absolute structure for the title compound, which has five chiral centres has been determined in this analysis. The supramolecular architecture comprises parallel zigzag chains formed through N—H⋯N and C—H⋯O hydrogen bonds, as well as intramolecular C—H⋯O, C—H⋯N and C—H⋯π interactions.


Structural commentary
In the title compound (I) (Fig. 1), the five-membered isoxazolidine ring has a twist conformation. The O1-N2 bond length in the isoxazolidine ring is 1.475 (6) Å which is close to the values in related compounds Molander & Cavalcanti, 2013). The cyclohexane ring adopts a chair conformation. The dihedral angle between the mean planes of the isoxazolidine and imidazolidinone rings is 73.1 (3) while the C8-C9-C10-O1 torsion angle is 74.7 (7) . In the molecule there are some short C-HÁ Á ÁO and C-HÁ Á ÁN contacts present (Table 1). The absolute configuration of (I) has been confirmed as C10(R),C12(S),C14(S),C16(R),C19(S) for the five arbitrarily numbered chiral centres in the molecule.

Supramolecular features
In the crystal packing of (I), the molecules are linked through an intermolecular N1-HN1Á Á ÁN2 i hydrogen bond (Table 1) and a weak N1-HN1Á Á ÁO1 i interaction [3.053 (8) Å ], forming undulating sheets parallel to the bc plane (Fig. 2). Within the chains, the molecules are stabilized by a weak intermolecular C3-H3Á Á ÁO2 ii hydrogen bond (Table 1). Also present in the crystal are 39.3 Å 3 solvent-accessible voids.

Figure 2
A view of the title structure, showing the molecules of the title compound arranged in zigzag parallel chains sustained by weak N-HÁ Á ÁN and N-HÁ Á ÁO hydrogen bonds.

Spectroscopic investigations
NMR spectra were recorded on a Bruker Avance II 300 MHz spectrometer operating at 300 MHz for 1 H and 75.46 MHz for 13 C and were referenced to tetramethylsilane ( = 0 p.p.m.). High-resolution (HR-ESI-QToF) mass spectra were recorded using a Bruker Micro ToF-Q II XL spectrometer.
The 1 H NMR spectrum of (I) shows the presence of an NH proton at 8.32 p.p.m. and the 13 C NMR spectrum confirms the existence of the C3 and C5 stereogenic centres at 66.4 p.p.m. and 78.0 p.p.m., respectively. The spectroscopic measurements are consistent with the crystal structure of (I). High-resolution mass spectrometry in the positive-ion mode exhibits an

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. All hydrogen atoms attached to C atoms were fixed geometrically and treated as riding with C-H = 0.98 Å (methine), 0.97 Å (methylene), 0.96 Å (methyl) and 0.93 Å (aromatic), with U iso (H) = 1.2U eq (C)(methine, methylene, aromatic) or 1.5U eq C(methyl). The H atom on the nitrogen N1 of the indole ring was found in a difference-Fourier map but was subsequently refined with the coordinates and isotropic displacement parameter also riding with U iso = 1.2 U eq (N). The bond length N1-HN1 was restrained to ensure proper geometry using the DFIX instruction of SHELXL2014/7 (Sheldrick, 2015). The absolute structure Flack parameter [À0.013 (13) for 1005 quotients (Parsons et al., 2013)] confirmed the configuration of the molecule as C10(R),C12(S),C14(S),C16(R),C19(S) for the five arbitrarily numbered chiral centres in the molecule. Reaction scheme for the synthesis of compound (I).  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.