Dimethyl 1,4-dihydro-4-(4-methoxyphenyl)-2,6-dimethylpyridine-3,5-dicarboxylate

In the title compound, C18H21NO5, the dihydropyridine ring adopts a flattened-boat conformation and its planar part forms a dihedral angle of 84.60 (2)° with the benzene ring. In the crystal, intermolecular N—H⋯O and C—H⋯O hydrogen bonds result in the formation of zigzag layers parallel to (001). These layers are interconnected via C—H⋯π interactions.


Experimental
Dimethyl 1,4-dihydro-2,6-dimethyl-4-(4-methoxyphenyl)-3,5-pyridine dicarboxylate was prepared according to the Hantzsch pyridine synthesis (Rathore et al., 2009). A mixture of 4-methoxybenzaldehyde (10.0 mmol), methylacetoacetate (20.0 mmol) and ammonium acetate (10.0 mmol) was heated at 353 K for 2 h (monitored by TLC). After the completion of the reaction, the mixture was cooled to room temperature and it was kept for 24 h to get a solid product. The solid formed was washed using diethyl ether. The washed solid was collected separately and the liquid kept for solidification. The purity of the crude product was checked through TLC and recrystallized using acetone and ether.

Refinement
Atom H1N1 was located in a difference Fourier map and was refined freely [N-H = 0.854 (18) Å]. The remaining H atoms were positioned geometrically [C-H = 0.93-0.98 Å] and were refined using a riding model, with U iso (H) = 1.2-1.5 U eq (C).
A rotating-group model was applied for the methyl groups. Reflection 010 was partially obscured by the beam stop and hence was omitted. In addition, the most disagreeable reflections 114, 414 amd 248 were also omitted during the refinement.

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K.
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 Rfactors(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.