(E)-3-Isopropyl-1-methyl-2,6-diphenylpiperidin-4-one O-nicotinoyl oxime

In the title compound, C27H29N3O2, the piperidine ring exists in a chair conformation with an equatorial orientation of the phenyl and methyl substituents. The C—C=N bond angles are significantly different [119.1 (2) and 127.2 (2)°]. The phenyl rings are inclined to one another by 44.90 (14)°, and by 80.85 (13) and 79.62 (12)° to the mean plane of the piperidine ring. The terminal pyridine ring is inclined to the piperidine ring mean plane by 74.79 (15)°. In the crystal, molecules are linked by C—H⋯π interactions, forming a three-dimensional network.

In the title compound, C 27 H 29 N 3 O 2 , the piperidine ring exists in a chair conformation with an equatorial orientation of the phenyl and methyl substituents. The C-C N bond angles are significantly different [119.1 (2) and 127.2 (2) ]. The phenyl rings are inclined to one another by 44.90 (14) , and by 80.85 (13) and 79.62 (12) to the mean plane of the piperidine ring. The terminal pyridine ring is inclined to the piperidine ring mean plane by 74.79 (15) . In the crystal, molecules are linked by C-HÁ Á Á interactions, forming a three-dimensional network.

Comment
The piperdin-4-one nucleus is an important class of pharmacophore due to its broad spectrum of biological actions ranging from antibacterial to anticancer (Parthiban et al., 2009;Narayanan et al., (2012). Hence, their synthesis and steriochemical analysis has gained much interest in the field of medicinal chemistry. Continuing our interest in such compounds (Vinuchakkaravarthy et al., 2013a,b) we have synthesized the title compound and report herein on its crystal structure.
The molecular structure of the title molecule is shown in Fig. 1. The piperidine ring N1/C1-C5 adopts a chair conformation with the deviations of atoms N1 and C3 from the mean plane through atoms C1/C2/C4/C5 being -0.6131 (19) and 0.6448 (25) Å, respectively. The smallest displacement asymmetry parameters (Nardelli, 1983)  In the crystal, the molecules are linked by C-H···π interactions (Table 1and Fig. 2) forming a three-dimensional structure.

Experimental
The intermediate 3-ethyl-2,6-diphenylpiperidin-4-one (I) was synthesized by Mannich condensation using benzaldehyde (2 mol), ammonium acetate (1 mol) and ethyl methyl ketone (1 mol) in absolute ethanol and warmed for 30 min and stirred overnight at room temperature. The product obtained was treated with methyl iodide in the presence of potassium carbonate and refluxed to give (I). The oximation of (I) was carried out by adding hydroxylamine hydrochloride in the presence of sodium acetate in ethanol and the mixture was refluxed for 2h. The resulting oxime (0.5 g, 1.55 mmol) was stirred with dry pyridine (5 ml), then 3-methylbenzoic acid (0.21 g, 1.7 mmol) was added followed by drop wise addition of phosphorus oxychloride (0.21 mL, 2.3 mmol) with stirring at ambient temperature for 15 min. Progress of the reaction was monitored by thin layer chromatography. Upon completion of the reaction saturated sodium bicarbonate solution was added and a white solid formed. It was filtered off and dried (Yield 0.58 g, 87.8%). This solid was recrystallized in ethanol to yield block-like colourless crystals of the title compound.

Refinement
H atoms were positioned geometrically and allowed to ride on their parent atoms: 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.  The molecular structure of the title molecule, with atom labelling. Displacement ellipsoids are drawn at the 30% probability level.

Figure 2
Two views of the crystal packing of the title compound, showing the C-H···π interactions (dashed lines; see Table 1  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.15 e Å −3 Δρ min = −0.14 e Å −3 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.