2,6-Diphenyl-3-(prop-2-en-1-yl)piperidin-4-one

In the title piperidine derivative, the molecules are linked by C—H⋯π interactions into dimers related by twofold symmetry.

In the title compound, C 20 H 21 NO, the dihedral angle between the phenyl ring is 47.5 (1) and the piperidine ring adopts a chair conformation. In the crystal, molecules are linked by C-HÁ Á Á interactions into dimers with the molecules related by twofold symmetry.

Structure description
Piperidine derivatives can act as enzyme stabilizers to improve therapeutic enzyme activity in Fabry patient cell lines (Li et al., 2018). Some of these derivatives possess antioxidant (Kim et al., 2016) and analgesic activities (Jahan et al., 2016). As part of our studies in this area, we now describe the synthesis and structure of the title compound (Fig. 1).
The piperidine ring adopts a chair conformation and each substituent adopts an equatorial disposition. The dihedral angles between the piperidine ring (all atoms) and the C6-C11 and C15-C20 benzene rings are 70.31 (11) and 79.00 (11) , respectively. The dihedral angle between the C6-C11 and C15-C20 benzene rings is 47.51 (12) . In the crystal, a C2-H2Á Á ÁCg i [Cg = is the centroid of the C6-C11 ring; symmetry code: (i) 1 À x, y, 1 2 À z) interaction occurs with H2AÁ Á ÁCg = 2.73 Å and C2-H2AÁ Á ÁCg = 148 . This leads to dimers with the molecules related by twofold rotation symmetry (Fig. 2). The N1-H1N grouping points towards the opposite face of the C6-C11 ring but the H1NÁ Á ÁCg separation of 3.15 Å is probably too long to be regarded as a bond.

Synthesis and crystallization
A mixture of hexene-2-one (0.05 mol), benzaldehyde (0.1 mol), ammonium acetate (0.05 mol) and ethanol (40 ml) was heated gently and poured into ether (50 ml) and data reports treated with concentrated hydrochloric acid (25 ml). The precipitated hydrochloride was washed with an ethanol-ether mixture. The base was liberated by adding strong ammonia until the hydrochloride dissolved. Dilution with water afforded the free base. The pure compound was was further recrystallized with benzene-petroleum ether to yield the title compound.

Figure 1
The molecular structure of the title compound, with the atom labelling. Displacement ellipsoids are drawn at the 30% probability level.

Figure 2
The crystal packing of the title compound viewed along the b-axis direction. The C-HÁ Á Á interactions are shown as dashed lines. For clarity H atoms not involved in these hydrogen bonds have been omitted. Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. Refinement. The C-bound H atoms were placed in idealized locations and refined as riding atoms. The N-bound H atom was located in a difference map and refined with a restraint.