Dimethyl 4-(4-formylphenyl)-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate

The title compound, C18H19NO5, is a product of the Hantzsch reaction of p-phthalaldehyde, methyl acetoacetate, and ammonium acetate. The 1,4-dihydropyridine ring of the molecule adopts a flattened boat conformation. The benzene ring is almost perpendicular to the 1,4-dihydropyridine ring; the plane through the six C atoms of the benzene ring and the plane through the four C atoms that form the base of the boat-shaped 1,4-dihydropyridine ring (excluding the ring N atom and the opposite ring C atom) make a dihedral angle of 87.60 (3)°. Intermolecular N—H⋯O hydrogen bonds result in the formation of extended chains along the a axis.

The title compound, C 18 H 19 NO 5 , is a product of the Hantzsch reaction of p-phthalaldehyde, methyl acetoacetate, and ammonium acetate. The 1,4-dihydropyridine ring of the molecule adopts a flattened boat conformation. The benzene ring is almost perpendicular to the 1,4-dihydropyridine ring; the plane through the six C atoms of the benzene ring and the plane through the four C atoms that form the base of the boatshaped 1,4-dihydropyridine ring (excluding the ring N atom and the opposite ring C atom) make a dihedral angle of 87.60 (3) . Intermolecular N-HÁ Á ÁO hydrogen bonds result in the formation of extended chains along the a axis.
The bond lengths and angles in (I) show normal values (Table 1) except for the geometry of the 1,4-dihydropyridine ring which adopts a flattened boat conformation with ring distortions at the nitrogen (Nl) and the tetrahedral carbon (C11). Both atoms are displaced to the same side of the ring with distances of 0.17Å and 0.39 Å, respectively, from the plane defined by C3, C4, C7, and C8, and thus form the apices of a boat-type conformation (Fossheim et al., 1982). The phenyl ring is almost perpendicular to the 1,4-dihydropyridine ring (N1-C4-C3-C11-C8-C7) with a dihedral angle of 92.40 (1)°.
The bisect plane of the 1,4-dihydropyridine ring defined by N1, C11, and C12 makes a dihedral angle of 35.40 (7)° with the phenyl ring. The intermolecular hydrogen bonds N1-H1···O5 i [symmetry code (i): −x + 1, −y + 2, −z + 2] between the pyridine N atom and a neighboring formyl O atom result in the formation of extended chains along the a axis ( Figure 2).

Experimental
The title compound,(I), was prepared by refluxing a mixture of p-phthaldehyde (0.67 g, 5.0 mmol), methyl acetoacetate (1.19 g, 10.25 mmol), and ammonium acetate (0.58 g, 7.5 mmol) for 6 h in water (10 ml), and purified by recrystallization, m.p.479-481 K. Single crystals suitable for X-ray diffraction were obtained by slow evaporation of an ethyl acetate solution.

Refinement
All non-hydrogen atoms were refined with anisotropic displacement parameters. Hydrogen atoms attached to anisotropically refined atoms were placed in geometrically idealized positions and included as riding atoms with C-H = 0.93Å and U iso (H) = 1.2*U eq (C) (aromatic); C-H = 0.96Å and U iso (H) = 1.5*U eq (C) (methyl); C-H = 0.98Å and U iso (H) = 1.2*U eq (C) (tertiary CH).