Isopropyl 1-benzoyl-4-benzoyloxy-2,6-diphenyl-1,2,3,6-tetrahydropyridine-3-carboxylate

In the title compound, C35H31NO5, the piperidine ring has an envelope conformation, with the phenyl-substituted C atom adjacent to the methylene C atom as the flap. This flap atom deviates by 0.633 (2) Å from the mean plane of the other five essentially coplanar atoms in the ring (r.m.s. deviation = 0.044 Å). Intramolecular C—H⋯O hydrogen bonds form S(7) and S(9) ring motifs. In the crystal, molecules are linked by pairs of C—H⋯O hydrogen bonds, forming inversion dimers with R 2 2(16) loops.

In the title compound, C 35 H 31 NO 5 , the piperidine ring has an envelope conformation, with the phenyl-substituted C atom adjacent to the methylene C atom as the flap. This flap atom deviates by 0.633 (2) Å from the mean plane of the other five essentially coplanar atoms in the ring (r.m.s. deviation = 0.044 Å ). Intramolecular C-HÁ Á ÁO hydrogen bonds form S(7) and S(9) ring motifs. In the crystal, molecules are linked by pairs of C-HÁ Á ÁO hydrogen bonds, forming inversion dimers with R 2 2 (16) loops.   Table 1 Hydrogen-bond geometry (Å , ).

Comment
Piperidine iminocyclitols have shown significant pharmacological results against HIV and in cancer therapy. Alkaloids containing the piperidine nucleus exhibited a promising wide range of biological activities such as antimicrobial, antiparasitic, cytotoxicity, anti-inflammatory, pesticidal and anti-HIV-1 properties (Mishra and Ghosh, 2011). The motivation for the biological trial arises as piperidine derivatives are an important class of heterocyclic compounds with potent pharmacological/biological activities (Ramachandran et al., 2011). Against this background, and in order to obtain detailed information on molecular conformations in the solid state, an X-ray study of the title compound was carried out.

Experimental
3-Isopropyl-2,6-diphenylpiperidin-4-one carboxylate were syntheized by Mannich condensation of benzaldehyde with isopropyl acetoacetate. Isopropyl acetoacetate (0.01 mol), benzaldehydes (0.02 mol) and ammonium acetate (0.01 mol) were taken in a 500 ml round bottom flask. Further ethanol (25 ml) was added to the flask, warmed for about 10 min. and set aside until the product crystallized. The product obtained was filtered and the solid product was collected and washed with cold water. The product was dried at room temperature and recrystallized from ethanol to obtain 3-isopropyl-2,6-diphenylpiperidin-4-one carboxylate. Equimolar amounts of 3-isopropyl-2,6-diphenylpiperidin -4-one carboxylate (3.37 g, 100 mmol), benzoyl chloride (2 ml, 100 mmol) ethylene triamine (2 ml, 200 mmol) and benzene (50 ml) were heated to reflux for 6-10 h. The reaction was monitored by TLC, after completion of the reaction solvent was washed with 2 N HCl followed by water. solvent was removed under vacuum and the residue was recrystalized form ethanol. The yield of the isolated product was 2.65 g (70%).

Refinement
All H atoms were fixed geometrically and allowed to ride on their parent C atoms, with C-H distances fixed in the range 0.93-0.97 Å with U iso (H) = 1.5U eq (C) for methyl H atoms and 1.2U eq (C) for all other H atoms.

Figure 1
The molecular structure of the title compound, showing the atomic numbering and displacement ellipsoids drawn at 30% probability level.  The crystal structure showing the centrosymmetric hydrogen bond motif R 2 2 (16). For the sake of clarity, the H atoms not involved in the motif have been omitted.

Isopropyl 1-benzoyl-4-benzoyloxy-2,6-diphenyl-1,2,3,6-tetrahydropyridine-3-carboxylate
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.