Crystal structure of 2-chloro-1-(3-methyl-2,6-diphenylpiperidin-1-yl)ethanone

In the title compound, C20H22ClNO, the piperidine ring has a twist-boat conformation. There is an intramolecular C—H⋯π interaction involving the two phenyl rings which are inclined to one another by 84.91 (7)°. In the crystal, molecules are linked via C—H⋯O hydrogen bonds, forming helical chains along [010]. The chains are linked by C—H⋯π interactions, forming sheets parallel to (100).


S1. Structural commentary
Piperidine and their derivatives are significant heterocyclic compounds found in natural substances (Jain et al., 2005).
They have been observed to exhibit a wide range of biological activities, such as anti-fungal, anti-malarial, anti-bacterial and anti-viral activities (Aridoss et al., 2007;Mobio et al., 1989). They also show a highly favourable antiviral activity against a range of primary HIV-1 isolates (Palani et al., 2002).
The molecular structure of the title compound is illustrated in Fig. 1. The sum of the bond angles around atom N1 is 359.85 (1) °, indicating sp 2 hybridization. The dihedral angle between the phenyl rings (C5-C10 and C16-C21) is 84.91 (7) °. They are linked by an intramolecular C-H···π interaction ( Table 1). The piperidine ring adopts a twist-boat conformation.
In the crystal, molecules are linked via C-H···O hydrogen bonds forming helical chains along [010], see Table 1 and  Table 1.

S2. Synthesis and crystallization
A mixture of t-3-methyl-r-2,c-6-diphenylpiperidine (5 mmol), chloroacetyl chloride (20 mmol) and triethylamine (20 mmol) in anhydrous benzene (20 ml) was stirred at rt. The precipitated ammonium salt was filtered and the resulting solution was washed with water and bicarbonate solution (4 × 10 ml). Finally, the benzene solution was dried over anhydrous sodium sulfate and concentrated. The pasty mass was purified by crystallization from pet-ether (333-353 K) and ethyl acetate in the ratio of 95: 5, and yielded colourless block-like crystals.

S3. Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1. H atoms were positioned geometrically and treated as riding on their parent atoms: C-H = 0.93 -0.98 Å, with U iso (H)= 1.5 U eq (C) for methyl H atoms and = 1.2U eq (C) for other H atoms.

Figure 1
The molecular structure of the title compound, with atom labelling. Displacement ellipsoids are drawn at the 30% probability level. The intramolecular C-H···π interaction is shown as a dashed line (see Table 1 for details).