Crystal structure of 1-(2-chloroacetyl)-2,6-bis(4-fluorophenyl)-3,3-dimethylpiperidin-4-one

In the title molecule, C21H20ClF2NO2, the piperidine ring adopts a slightly-distorted boat conformation, the two benzene rings form a dihedral angle of 87.43 (1)° and a weak intramolecular C—H⋯π interaction is observed. In the crystal, weak C—H⋯O hydrogen bonds and weak C—H⋯π interactions connect molecules forming a three-dimensional network.


Chemical context
Piperidones are an important group of heterocyclic compounds in the field of medicinal chemistry due to their biological activities, which include cytotoxic properties (Dimmock et al., 2001). They are also reported to possess analgesic, anti-inflammatory, central nervous system (CNS), local anaesthetic, anticancer and antimicrobial activities (Perumal et al., 2001). The present investigation was undertaken to establish the molecular structure, the conformation of the heterocyclic ring and the orientation of the 4-fluorophenyl groups with respect to each other.

Synthesis and crystallization
The synthesis followed the procedure of Aridoss et al. (2007).

Figure 2
Part of the crystal structure showing weak hydrogen bonds as dashed lines. H atoms not involved in the hydrogen bonds or weak C-HÁ Á Á stacking interactions are not shown.

Figure 1
The molecular structure of the title compound, showing 30% probability displacement ellipsoids.
14.4 mmol) in benzene (20 ml), dichloroacetylchloride (1 ml, 10 mmol) in benzene (20 ml) was added dropwise for about half an hour. Stirring was continued with mild heating using a magnetic stirrer for 7 h. The progress of the reaction was monitored by TLC. After the completion of reaction, it was poured into water and extracted with ether. The collected ether extracts were then washed well with 3% sodium bicarbonate solution and dried over anhydrous Na 2 SO 4 . The pasty mass obtained was purified by crystallization from a benzenepetroleum ether solution (333-353 K) in the ratio of 95:5. X-ray quality crystals were grown by slow evaporation of an ethanol solution of the title compound at ambient temperature.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. All H atoms were placed in calculated positions (C-H = 0.93-0.97 Å ) and included in the refinement in a riding-model approximation with U iso (H) = 1.2U eq (C) or 1.5U eq (C methyl ).

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.