1-Chloroacetyl-2,6-bis(3-fluorophenyl)piperidin-4-one

In the title compound C19H16ClF2NO2, the piperidone ring adopts a twist-boat conformation with the two out-of-plane atoms deviating by 0.544 (1) and 0.511 (1) Å from the plane through the remaining atoms in the ring. Sterically favoured non-H-atom C⋯O intermolecular contacts are observed in the structure, within a 3.00 Å range. The crystal packing is stabilized by C—H⋯O and C—H⋯F hydrogen bonds and an intermolecular π–π interaction [centroid-centroid separation of 3.783 (1) Å]. Alternating C—H⋯O and C—H⋯F intermolecular interactions generate chains running along the a axis, while a centrosymmetric R 2 2(16) ring involving C—H⋯O interactions is formed centred at (1/2, 1/2, 0).


S1. Comment
Amides are a prominent functional group in chemistry due to their being an integral part in biologically important polymers such as peptides and proteins. Functionalized piperidines are among the most common building blocks in natural products, and, more interestingly, in many biologically active compounds such as anopterine, pergoline, scopolamine and morphine (Richardo et al., 1979, Schneider, 1996, Mukhtar & Wright, 2005. Piperidones also have high impact in medicinal field owing to their role as key chiral intermediates for the preparation of a variety of natural, synthetic and semi-synthetic pharmacophores with marked anticancer (Fleet et al., 1990) and anti-HIV activities (Winkler & Holan, 1989). Particularly, amides derived from 2,6-diarylpiperidin-4-ones exhibited marked antibacterial and antitubercular activities (Aridoss et al. 2007a(Aridoss et al. , 2009a. As a corollary of these interesting biological and pharmaceutical properties and synthetic utility, substantial interest has been demonstrated towards 2,6-diarylpiperidin-4ones (Krishnapillay et al., 2000, Aridoss et al., 2007b. Recently, we have disclosed the crystal structures of variously substituted 2,6-diarylpiperidin-4-ones and their derivatives (Gayathri et al. 2008, Ramachandran et al., 2008, Aridoss et al., 2009b. In the interest of above, crystal structure of 1-chloroacetyl-2,6-bis (3-fluorophenyl)-piperidin-4-one is reported here.

S2. Experimental
The title compound was obtained by adopting our earlier method (Aridoss et al. 2007a) with slight modification. To a solution of 2,6-bis(3-fluorophenyl)-piperidin-4-one (1 equiv.) and NEt 3 (1.5 equiv.) in freshly distilled benzene, chloroacetyl chloride (1 equiv.) in benzene was added drop wise. Stirring was continued until the completion of reaction. Later, it was poured into water and extracted with ethyl acetate. The combined organic extract was then washed well with a 3% sodium bicarbonate solution, brined and dried over anhydrous sodium sulfate. This, upon evaporation and subsequent recrystallization of the title compound in distilled ethanol afforded fine crystals suitable for X-ray diffraction study.

Figure 1
The molecular structure of the title compound(I), showing 30% probability displacement ellipsoids.

Figure 2
The molecular packing of (I), viewed approximately along the b axis, showing C-H···O and C-H···F hydrogen bonds, drawn as thick dashed lines, and π-π intermolecular interaction, drawn as narrow dashed lines. For clarity, hydrogen atoms which are not involved in hydrogen bonding are omitted.

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.