Ethyl 3-methyl-2,6-diphenylpiperidine-1-carboxylate

In the title compound, C21H25NO2, the piperidine ring adopts a twisted boat conformation characterized by puckering parameters θ = 89.5 (1) and ϕ = 257.5 (2)°. The phenyl groups are located in equatorial and axial positions on the central piperidine ring, while the methyl group is in an equatorial position. The dihedral angle between the phenyl rings is 49.8 (1)°. An intramolecular C—H⋯O interaction occurs. The crystal structure features weak intermolecular C—H⋯O interactions and a stabilizing intermolecular C—H⋯π contact involving the axial phenyl ring.

In the title compound, C 21 H 25 NO 2 , the piperidine ring adopts a twisted boat conformation characterized by puckering parameters = 89.5 (1) and ' = 257.5 (2) . The phenyl groups are located in equatorial and axial positions on the central piperidine ring, while the methyl group is in an equatorial position. The dihedral angle between the phenyl rings is 49.8 (1) . An intramolecular C-HÁ Á ÁO interaction occurs. The crystal structure features weak intermolecular C-HÁ Á ÁO interactions and a stabilizing intermolecular C-HÁ Á Á contact involving the axial phenyl ring.
The phenyl rings at C2 and C6 atoms are oriented in the axial and equatorial positions, respectively, and the dihedral angle between them is 49.8 (1)°. Similarly, the methyl group at C5 is also oriented in equatorial position. All these substitutions are confirmed by the respective torsion angles. In addition, the substitution of ethylacetate group on N1 atom showed extended conformation with respect to the piperidine ring, which is also confirmed by the torsion angles.
The packing diagram of the title compound viewed down a-axis is shown in Fig. 2. The molecules did not present any classical H-bonds. However, the molecules are involved in weak intra-and intermolecular C-H···O interactions (Table   1), which stabilize the molecules in the crystal packing. Interestingly, a C-H···π interaction (C3-H3B···Cg1; Cg1 is the centroid of the ring C13···C18) also helps for the crystal packing.

Experimental
The compound, 3-methyl-2,6-diphenylpiperidin-4-one was obtained by adopting an earlier method (Sampath et al., 2003;Noller & Baliah, 1948) and it was reduced using amalgamated zinc in aqueous methanol solution in the presence of HCl, giving 3-methyl-2,6-diphenylpiperidine as a product. To a well stirred solution of 3,5-dimethyl-2,6-diphenylpiperidin-4-one (2 mM) and triethylamine (4 mM) in freshly distilled benzene (50 ml), a little excess amount of ethylchloroacetate (2.2 mM) in benzene (10 ml) was added drop-wise over about half an hour and stirring was continued until the completion of reaction. The reaction mixture was then poured into water and extracted with dichloromethane. Recrystallization of the title compound using pure ethanol resulted in suitable colorless crystals.

Refinement
H atoms were positioned geometrically and refined using a riding model with C-H = 0.93 Å for aromatic H, 0.97 Å for methylene, 0.98 Å for methine, and 0.96 Å for methyl H atoms. The U iso parameters for H atoms were constrained to be 1.5U eq of the carrier atom for the methyl H atoms and 1.2U eq of the carrier atom for the remaining H atoms.