(E)-1,3-Dimethyl-2,6-diphenylpiperidin-4-one O-(phenoxycarbonyl)oxime

The title piperidine derivative, C26H26N2O3, has an E conformation about the N=C bond. The piperidine ring has a chair conformation and its mean plane is almost perpendicular to the attached phenyl rings, making dihedral angles of 87.47 (9) and 87.34 (8)°. The planes of these two phenyl rings are inclined to one another by 60.38 (9)°. The plane of the terminal phenyl ring is tilted at an angle of 32.79 (9)° to the mean plane of the piperidine ring. The molecular conformation is stabilized by two intramolecular C—H⋯O contacts. There are no significant intermolecular interactions in the crystal.

The title piperidine derivative, C 26 H 26 N 2 O 3 , has an E conformation about the N C bond. The piperidine ring has a chair conformation and its mean plane is almost perpendicular to the attached phenyl rings, making dihedral angles of 87.47 (9) and 87.34 (8) . The planes of these two phenyl rings are inclined to one another by 60.38 (9) . The plane of the terminal phenyl ring is tilted at an angle of 32.79 (9) to the mean plane of the piperidine ring. The molecular conformation is stabilized by two intramolecular C-HÁ Á ÁO contacts. There are no significant intermolecular interactions in the crystal.

Related literature
For the biological activity of piperidine derivatives, see, for example: Moldt et al. (1997); Peters et al. (2009). For asymmetry parameters, see: Nardelli (1983 Table 1 Hydrogen-bond geometry (Å , ). Supporting information for this paper is available from the IUCr electronic archives (Reference: SU2678).

Comment
In view of the biological importance of piperidine derivatives (Moldt et al., 1997;Peters et al., 2009) we undertook the synthesis of the title compound and report herein on its crystal structure.
In the crystal, there are no significant intermolecular interactions present (Fig. 2).

Experimental
The title compound was synthesized by Mannich condensation. Benzaldehyde (2 mol), ammonium acetate (1 mol) and ethyl methyl ketone (1 mol) in absolute ethanol were warmed for 30 min and then stirred overnight at room temperature.
The product obtained was treated with methyl iodide (1.5 mol) in the presence of potassium carbonate (2 mol) in acetone (10 ml) and the mixture was refluxed to give 1,3-dimethyl-2,6-diphenylpiperidin-4-one (I). Oximation was carried out by refluxing (I) with hydroxylamine hydrochloride (2 mol) in the presence of sodium acetate (2 mol) in ethanol (10 ml). To the resulting oxime (0.5 g, 1.79 mmol) in dry tetrahydrofuran (10 ml), was added potassium carbonate (0.48 g, 3.52 mmol) followed by tetrabutylammonium bromide (0.58 g,1.79 mmol). After stirring for 15 min, phenyl chloroformate (0.38 g, 2.68 mmol) was added drop wise over a period of 15 min. The mixture was stirred at ambient temperature for 2 h and progress of the reaction was monitored by thin layer chromatography. Upon completion of the reaction, the mixture was diluted with water (20 ml) and extracted with dichloromethane (2 × 20 ml). The combined organic layers were washed with water (2 × 20 ml), then brine solution (20 ml), and then dried over anhydrous sodium sulfate (5 g). The mixture was the filtered and concentrated under reduced pressure. The crude product obtained was purified by column chromatography over silica gel (100-200 mesh) eluted with a solvent system of ethyl acetate:petroleum ether (2:98). The pure fractions were collected and concentrated under reduced pressure giving a white solid (0.63 g, 85%). This was recrystallized from a DMF-water mixture (9:1) to yield colourless block-like crystals suitable for X-ray diffraction studies.

Refinement
All the H atoms were positioned geometrically and constrained to ride on their parent atom: C-H = 0.93-0.98 Å with U iso (H) = 1.5U eq (C-methyl) and = 1.2U eq (C) for other H atoms.   A view along the b axis of the crystal packing of the title compound.  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.