Ethyl 4-(5-chloro-3-methyl-1-phenyl-1H-pyrazol-4-yl)-6-methyl-2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate

In the title compound, C18H19ClN4O3, the dihydropyrimidinone ring adopts a flattened boat conformation. The dihedral angle between the phenyl and pyrazole rings is 43.39 (6)°. An intramolecular C—H⋯O contact generates an S(8) ring motif that stabilizes the molecular conformation and precludes the carbonyl O atom of the ester group from forming intermolecular interactions. Molecules are linked into centrosymmetric dimers by pairs of N—H⋯O hydrogen bonds and the dimers are linked into infinite chains along [101] by N—H⋯N hydrogen bonds.

In the title compound, C 18 H 19 ClN 4 O 3 , the dihydropyrimidinone ring adopts a flattened boat conformation. The dihedral angle between the phenyl and pyrazole rings is 43.39 (6) . An intramolecular C-HÁ Á ÁO contact generates an S(8) ring motif that stabilizes the molecular conformation and precludes the carbonyl O atom of the ester group from forming intermolecular interactions. Molecules are linked into centrosymmetric dimers by pairs of N-HÁ Á ÁO hydrogen bonds and the dimers are linked into infinite chains along [101] by N-HÁ Á ÁN hydrogen bonds.

Comment
Pyrimidinones have drawn widespread attention due to their medicinal applications (Atwal, 1990). A variety of dihydropyrimidinone derivatives have been screened for anti-hypertension (Desai et al., 2006), anti-bacterial and anti-carcinogenic (Wipf & Cunningham, 1995), and anti-tuberculosis activity (Bedia et al., 2006). Prompted by these observations and in continuation of our work in this area, herein we report the crystal structure of the title compound, (I).
In (I), Fig. 1, the dihydropyrimidinone ring adopts a flattened boat conformation. The dihedral angle between the phenyl ring and the pyrazole ring is 43.39 (6)°. Bond lengths and angles are within normal ranges and comparable to a related structure (Fun et al., 2009). An intramolecular C18-H18C···O3 contact generates a S(8) ring motif (Bernstein et al., 1995) which stabilises the molecular conformation and precludes the O3 atom from forming intermolecular contacts. The molecules are linked into centrosymmetric dimers by N-H···O hydrogen bonds (Table 1)
After cooling the reaction mixture to room temperature, the contents were poured into ice-cold water (100 ml). The solid mass separated was collected by filtration and dried. Crystals were obtained from ethanol by slow evaporation (Yield 59%).

Refinement
The N-bound H atoms were located in a difference Fourier map and refined freely. The remaining H atoms were positioned geometrically and refined using a riding model with C-H = 0.93-0.98 Å, and with U iso (H) = 1.2 or 1.5 U eq (C). A rotating-group model was applied for the methyl groups. Fig. 1. The molecular structure of (I) with atom labels and 50% probability ellipsoids for non-H atoms. An intramolecular C-H···O contact is shown as dashed lines.
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 > 2sigma(F 2 ) is used only for calculating R-factors(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