1-[2,4,6-Trimethyl-3,5-bis(4-oxopiperidin-1-ylmethyl)benzyl]piperidin-4-one

In the structure of the title compound, C27H39N3O3, each of the (4-oxopiperidin-1-yl)methyl residues adopts a flattened chair conformation (with the N and carbonyl groups being oriented to either side of the central C4 plane) and they occupy positions approximately orthogonal to the central benzene ring [Cbenzene—C—Cmethylene—N torsion angles 103.4 (2), −104.4 (3) and 71.9 (3)°]; further, two of these residues are oriented to one side of the central benzene ring with the third to the other side. In the crystal packing, supramolecular layers in the ab plane are sustained by C—H⋯O interactions.

In the structure of the title compound, C 27 H 39 N 3 O 3 , each of the (4-oxopiperidin-1-yl)methyl residues adopts a flattened chair conformation (with the N and carbonyl groups being oriented to either side of the central C 4 plane) and they occupy positions approximately orthogonal to the central benzene ring [C benzene -C-C methylene -N torsion angles 103.4 (2), À104.4 (3) and 71.9 (3) ]; further, two of these residues are oriented to one side of the central benzene ring with the third to the other side. In the crystal packing, supramolecular layers in the ab plane are sustained by C-HÁ Á ÁO interactions.
VV is grateful to DST India for funding through the Young Scientist Scheme (Fast Track Proposal). TN acknowledges the establishment of the CCD facility under the IRHPA-DST programme at the Indian Institute of Science, Bangalore.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: HG2682).

Comment
Piperidin-4-one and their analogous pyran and thiopyran species attract interest owing to their biological properties, viz.
In compound (I), Fig. 1, the (4-oxopiperidin-1-yl)methyl residues containing the N1 and N2 atoms lie to one side of the central benzene ring and that with the N3 atom to the other. Owing to the presence of methyl substituents on either side of each 4-oxopiperidin-1-yl)methyl residue, the piperidin-4-one rings adopt side-on conformations to minimise steric interactions so that the N atoms occupy positions approximately normal to the plane through the benzene rings. This is quantified by the C2-C1-C7-N1 [103.4 (2) °], C2-C3-C14-N2 [-104.4 (3) °], and C4-C5-C21-N3 [71.9 (3) °] torsion angles. Each of the six-membered piperidin-4-one rings adopts a slightly flattened chair conformation with the N and carbonyl groups lying to either side of the central C 4 plane in each case. Only the amine-N3 atom forms a significant intra-or inter-molecular interaction, i.e. an intramolecular C-H···N contact, Table 1. In the crystal packing, molecules are sustained into layers by C-H···O interactions; Table 1. Layers are formed in the ab plane and stack along the c axis, Fig. 2.

Experimental
To a suspension of 1.5 equiv. of 4-piperidone hydrochloride monohydrate in benzene (20 ml), 3.0 equiv of K 2 CO 3 was added. After stirring well for 30 min, 2,4,6-tris(bromomethyl)mesitylene (0.5 equiv) in benzene (10 ml) was added, followed by refluxing for 10 h. The completion of reaction was monitored by TLC. The reaction mixture was then allowed to cool to room temperature, filtered to remove the insoluble solids and then the filter cake was washed with dichloromethane. Excess solvents were removed under reduced pressure and the obtained crude product was purified by crystallization using 1:1 ratio of chloroform and methanol; m.pt. 483 K.

Refinement
Carbon-bound H-atoms were placed in calculated positions (C-H 0.96 to 0.97 Å) and were included in the refinement in the riding model approximation, with U iso (H) set to 1.2-1.5U equiv (C).