2,4-Bis(furan-2-yl)-1,5-dimethyl-3-azabicyclo[3.3.1]nonan-9-one

In the title compound, C18H21NO3, the bicyclic ring system adopts a twin-chair conformation. The two methyl groups attached to the bicycle are in an equatorial orientation for both rings. One of the furan rings is disordered over two orientations with an occupancy ratio of 0.686 (6):0.314 (6). In the crystal, very long N—H⋯O hydrogen bonds connect the molecules into a chain perpendicular to the ac plane.

In the title compound, C 18 H 21 NO 3 , the bicyclic ring system adopts a twin-chair conformation. The two methyl groups attached to the bicycle are in an equatorial orientation for both rings. One of the furan rings is disordered over two orientations with an occupancy ratio of 0.686 (6):0.314 (6). In the crystal, very long N-HÁ Á ÁO hydrogen bonds connect the molecules into a chain perpendicular to the ac plane.

Comment
Molecules with the 3-azabicyclo[3.3.1]nonane nucleus are of great interest due to their presence in a wide variety of naturally occurring diterpenoid/norditerpenoid alkaloids and their broad-spectrum biological activities such as antimicrobial, analgesic, antogonistic, anti-inflammatory, local anesthetic hypotensive activity and so on (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 investigations are of interest in the field of medicinal chemistry. Also, the stereochemistry of the synthesized molecules is a major criterium for their biological response. Hence, it is important to establish the stereochemistry of the bio-active molecules. As a consequence, the present study was undertaken to examine the configuration and conformation of the synthesized title compound.

Experimental
The title compound was obtained by condensation of 2,6-dimethylcyclohexanone, furfuraldehyde and ammonium acetate in 1:2:1 ratio in ethanol. The reaction mixture was warmed and stirred until the completion of reaction. The crude product was washed with an ethanol -ethyl ether (1:5) mixture and recrystallized from ethanol -chloroform (1:1) to obtain the pure compound.

Refinement
The methyl H atoms were constrained to an ideal geometry (C-H = 0.96 Å) with U iso (H) = 1.5U eq (C), but were allowed to rotate freely about the C-C bonds. All remaining H atoms were placed in geometrically idealized positions (C-H = 0.93-0.98 Å) and constrained to ride on their parent atoms with U iso (H) = 1.2U eq (C). In order to bring the U ij parameters of the disordered atoms to the tolerant levels the restraints SADI, SIMU and ISOR were used.

Figure 1
View of the molecule of the title compound showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level. H atoms are represented by circles of arbitrary radii.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > σ(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.