1-Formyl-r-2,c-6-bis(4-methoxyphenyl)-t-3-methylpiperidin-4-one

The asymmetric unit of the title compound, C21H23NO4, contains two crystallographically independent molecules A and B. In both molecules, the piperidine-4-one rings adopt a distorted twist-boat conformation. The formyl group at position 1, the methoxyphenyl ring at position 2 and the methyl group at position 3 are attached equatorially. The methoxy phenyl ring at position 6 has an axial orientation. The dihedral angle between the two benzene rings is 55.27 (8)° in molecule A, and 55.29 (8)° in molecule B. In the crystal, the molecules are linked by weak C—H⋯O intermolecular hydrogen-bond interactions. In addition, weak C—H⋯π intermolecular interactions involving the benzene rings at positions 6 and 2 of molecule B are also found in the crystal structure.

The asymmetric unit of the title compound, C 21 H 23 NO 4 , contains two crystallographically independent molecules A and B. In both molecules, the piperidine-4-one rings adopt a distorted twist-boat conformation. The formyl group at position 1, the methoxyphenyl ring at position 2 and the methyl group at position 3 are attached equatorially. The methoxy phenyl ring at position 6 has an axial orientation. The dihedral angle between the two benzene rings is 55.27 (8) in molecule A, and 55.29 (8) in molecule B. In the crystal, the molecules are linked by weak C-HÁ Á ÁO intermolecular hydrogen-bond interactions. In addition, weak C-HÁ Á Á intermolecular interactions involving the benzene rings at positions 6 and 2 of molecule B are also found in the crystal structure. H atoms treated by a mixture of independent and constrained refinement Á max = 0.69 e Å À3 Á min = À0.24 e Å À3 Table 1 Hydrogen-bond geometry (Å , ). Symmetry codes: (i) x; y þ 1; z; (ii) x; y; z À 1; (iii) x; y À 1; z À 1; (iv) Àx þ 1; Ày; Àz;

S1. Comment
Piperidin-4-ones and their derivatives show a broad spectrum of biological activities which includes antimicrobial, antiviral, anti tuberculosis and anticancer activities and could also be used against multidrug resistant organisms (Aridoss et al., 2008). 2,6-Diarylpiperidin-4-one based chemical entities act as antineoplastic agents (Pati et al., 2008). Recent efforts devoted to 2,6-diarylpiperidin-4-one based chemical entities and establishing their stereochemistry (Ponnuswamy et al., 2002), (Venkatraj et al., 2008) are significant because the pharmacological effects of potential new drugs depends on the stereochemistry and ring conformations of these compounds.
The asymmetric unit of the title compound, C 21 H 23 NO 4 , contains two crystallographically independent molecules A and B (Fig. 1, Fig. 2). In both molecules, the piperidine ring adopts a distorted twist boat conformation. The formyl group at 1, the methoxy phenyl ring at 2 and the methyl group at 3 are attached equatorially. The methoxy phenyl ring at 6 has an axial orientation. The dihedral angle between the two benzene rings is 55.27 (8)° in molecule A; and 55.29 (8)° in molecule B. Compound(I) is chiral: in the arbitrarily chosen asymmetric molecules, C2A(C2B), C3A(C3B) and C6A(C6B) have S, R and R conformations respectively. The molecules are linked by weak C-H···O intermolecular hydrogen bond interactions ( Fig. 3; Table 1). In addition, weak C2A-H2A···π and C12A-H12B···π intermolecular interactions involving the benzene rings at positions 6(C61B-C66B) and 2(C21B-C26B) of molecule B are also found in the crystal structure.

S3. Refinement
Atoms H11A at C11A and H11B at C11B were located in a difference Fourier map and refined isotropically. Remaining H atoms were positioned geometrically and allowed to ride on their parent atoms, with C-H = 0.95, 0.98, 0.99 and 1.00 Å for Csp 2 , methyl, methylene and methine C, respectively; U iso (H) = kU eq (C), where k = 1.5 for methyl and 1.2 for all other H atoms. The maximum residual electron density peak 0.685 e Å -3 is located 2.23Å from H5A.  The molecular structure of independent molecule A, showing the atom-numbering scheme and displacement ellipsoids drawn at the 40% probability level(arbitary spheres for H atoms).

Figure 2
The molecular structure of independent molecule B, showing the atom-numbering scheme and displacement ellipsoids drawn at the 40% probability level(arbitary spheres for H atoms).  The packing of the title compound, viewed down the a axis. Dashed lines indicate weak C-H···O hydrogen bond intermolecular interactions. H atoms not involved in hydrogen bonding have been omitted.

1-Formyl-r-2,c-6-bis(4-methoxyphenyl)-t-3-methylpiperidin-4-one
Special details Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles 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 > 2σ(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.