1-Formyl-c-3,t-3-dimethyl-r-2,c-6-diphenylpiperidin-4-one

In the title compound, C20H21NO2, the piperidine ring adopts a distorted boat conformation. The phenyl rings substituted at the 2- and 6-positions of the piperidine ring subtend angles of 86.0 (1) and 67.3 (1)° with the mean plane of the piperidine ring (all six non-H atoms). The crystal packing features C—H⋯O interactions.

In the title compound, C 20 H 21 NO 2 , the piperidine ring adopts a distorted boat conformation. The phenyl rings substituted at the 2-and 6-positions of the piperidine ring subtend angles of 86.0 (1) and 67.3 (1) with the mean plane of the piperidine ring (all six non-H atoms). The crystal packing features C-HÁ Á ÁO interactions.

Comment
Piperidine derivatives are the valued heterocyclic compounds in the field of medicinal chemistry. The compounds possessing an amide bond linkage have a wide range of biological activities such as antimicrobial, anti-inflammatory, antiviral, antimalarial and general anesthetics (Aridoss et al., 2009). Functionalized piperidines are familiar substructures found in biologically active natural products and synthetic pharmaceuticals (Michael, 2001;Pinder, 1992;Rubiralta et al., 1991). Piperidines have been found to exhibit blood cholesterol-lowering activities (Nalanishi et al., 1974). Against this background and to ascertain the molecular structure and conformation, the X-ray crystal structure determination of the title compound has been carried out.
The ORTEP plot of the molecule is shown in Fig. 1. The formyl substituted piperidine derivative crystallizes in monoclinic space groups P2 1 /n. The piperidine ring adopts distorted boat conformation with the puckering parameters (Cremer & Pople, 1975) and the asymmetry parameters (Nardelli, 1983)  The crystal packing reveals that the symmetry related molecules are linked through a network of C-H···O type of intermolecular interactions. The atom C6 at (x, y, z) donates a proton to O1 at (-1/2 + x, 1/2 -y, -1/2 + z) forming a C (5) one dimensional chain running along the ac diagonal axis (Bernstein et al., 1995).

Experimental
To ice-cold acetic anhydride (10 ml), 85% formic acid (5 ml) was added slowly and the resulting acetic acid-formic anhydride was cooled to 5° C and added slowly to a cold solution of piperidine-4-one (5 mmol) in anhydrous benzene (30 ml). The reaction mixture was stirred at room temperature for 5 h and the solution was poured into water (250 ml). The benzene layer was separated out, concentrated and recrystallized from benzene: pet-ether (60-80° C) in the ratio 1:1.

Refinement
H atoms were positioned geometrically (C-H = 0.93-0.97 Å) and allowed to ride on their parent atoms, 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 50% probability level.  The crystal packing of the molecules. H atoms not involved in hydrogen bonding (dashed lines) have been omitted for clarity.

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.