Crystal structure of methyl 2-[2,4-bis(4-fluorophenyl)-3-azabicyclo[3.3.1]nonan-9-ylidene]hydrazinecarboxylate

In the title compound, the bicyclic ring system adopts a twin-chair conformation. In the crystal, N—H⋯O, C—H⋯O and C—H⋯F interactions connect the molecules, forming supramolecular chains propagating along the b-axis direction.

In the title compound, C 22 H 23 F 2 N 3 O 2 , the bicyclic ring system exists in a twinchair conformation with an equatorial disposition of the 4-fluorophenyl groups on the heterocycle. These aromatic rings are inclined to one another by 19.4 (1) . In the crystal, molecules are linked by pairs of N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds into inversion dimers, incorporating R 1 2 (7) and R 2 2 (8) ring motifs; the same O atom accepts both hydrogen bonds. These dimers are further linked by a pair of C-HÁ Á ÁF hydrogen bonds, enclosing R 2 2 (28) ring motifs, forming supramolecular chains along [010]. The NH group of the pyridine ring is not involved in hydrogen bonding, probably due to the steric hindrance of the fluorophenyl groups.

Chemical context
Molecules containing the 3-azabicyclo[3.3.1]nonane nucleus are of great interest due to their presence in a wide range of naturally occurring diterpenoid/norditerpenoid alkaloids and their broad-spectrum biological activities, such as antimicrobial, analgesic, antagonistic, anti-inflammatory and local anesthetic hypotensive activity (Parthiban et al., 2009;Hardick et al., 1996;Jeyaraman & Avila, 1981). Hence, the synthesis of new molecules with the 3-azabicyclo[3.3.1]nonane nucleus and their stereochemical investigation are of interest in the field of medicinal chemistry. Also, the stereochemistry of such molecules is a major criterium for their biological response. As a consequence, the present study was undertaken to examine the configuration and conformation of the synthesized title compound.

Figure 2
Partial view of the crystal packing of the title compound, showing the hydrogen bonds as dashed lines (see Table 1 for details). H atoms not involved in hydrogen bonding have been omitted for clarity).

Figure 1
The molecular structure of the title molecule (I), showing the atomlabelling scheme. Displacement ellipsoids are drawn at the 30% probability level.

Synthesis and crystallization
A mixture of 2,4-diphenyl-3-azabicyclo[3.3.1]nonan-9-one (0.1 mmol), methyl hydrazinecarboxylate (1.5 mmol) in an ethanol-chloroform (1:1 v/v) medium, with the addition of few drops of acetic acid, was stirred for 10-12 h. After completion of the reaction a solid mass was formed. The precipitate was filtered off and washed with an ethanol-water mixture. The crude product was then recrystallized from ethanol-chloroform to obtain colourless diffraction-quality crystals of title compound.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. All H atoms were positioned geometrically and constrained to ride on their parent atom, with N-H = 0.86 Å and C-H = 0.93-0.97 Å , and with U iso (H) = 1.5U eq (C) for methyl H atoms and 1.2U eq (N,C) for all other H atoms.  Data collection: SMART (Bruker, 2002); cell refinement: SAINT (Bruker, 2002); data reduction: SAINT (Bruker, 2002); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia (2012); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and PLATON (Spek, 2009). where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.52 e Å −3 Δρ min = −0.44 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. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.