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

The title molecule, C17H19NO5, was prepared by a Hantzsch dihydropyridine synthesis from 4-hydroxybenzaldehyde, methyl acetoacetate and NH4HCO3. In the molecular structure of the title compound, the dihydropyridine ring adopts a flattened boat conformation and the plane of the base of the boat forms a dihedral angle of 80.8 (2)° with the aromatic six-membered ring. The packing is stabilized by strong intermolecular N—H⋯Ocarbonyl, Ohydroxy—H⋯Ocarbonyl and weak intramolecular C—H⋯O hydrogen bonds.

However, the use of high temperatures, expensive metal precursors, catalysts that are harmful to the environment, and long reaction times limit the use of many of these methods. Herein, we report a mild and catalyst-free synthesis based on a variation of the commonly used Hantzsch dihydropyridine synthesis (Tamaddon et al., 2010), and the crystal structure of the resultant title compound is presented. Compared to the classical method involving the three-component coupling of an aldehyde with ethyl acetoacetate, and ammonia in acetic acid or in refluxing alcohol, the reation was conducted in water and avoided the use of catalysts, so it was very environmentally benign. Moreover, the workup is very simple and can give the product in high yield after simple filtration.
In the molecular structure of the title compound ( Fig. 1), atoms C7 and N1 deviate from the mean plane of atoms C8/C9/ C10/C11 in the same direction, by 0.45 (0) and 0.18 (7) Å, respectively, so the heterocyclic ring adopts a boat conformation.
In addition, the phenol ring substituent is almost perpendicular to the plane of the atoms C8/C9/C10/C11, with a dihedral angle between them of 80.8 (2)°. The methyl groups are nearly coplanar with the aformentioned plane of the atoms C8/C9/ C10/C11, with the methyl C atoms C12 and C13 deviating from the mean plane by 0.12 (4) and 0.22 (2) Table 1 for numerical values and symmetry operators).

Experimental
The title compound was obtained according to a reported method (Tamaddon et al., 2010). A mixture of 4-hydroxybenzaldehyde (2 mmol), methyl acetoacetate (4 mmol), and NH 4 HCO 3 (2 mmol) was stirred in water (2 mL) under reflux. After completion of the reaction (TLC monitoring), the mixture was diluted with cold water (20 mL) and filtered to obtain the pre-

Refinement
All H atoms were located in a difference map and refined isotropically. The N-H distance of H1A atom (for N1) was constrained to 0.86 Å. All other H atoms were positioned geometrically and treated as riding, with C-H distances in the range 0.93-0.98 Å, an O-H distance of 0.82 Å and U iso (H) = 1.2 or 1.5 times U eq (C). The methyl groups were allowed to rotate during the refinement. Fig. 1. Molecular structure of the title compound, showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. Dimethyl 4-(4-hydroxyphenyl)-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate

Special details
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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq N1 0.6521 (