Crystal structure of ethyl 6-chloromethyl-2-oxo-4-(2,3,4-trimethoxyphenyl)-1,2,3,4-tetrahydropyrimidine-5-carboxylate

The dihydropyrimidine ring in the title ester adopts a flattened envelope conformation. An intramolecular C—H⋯O hydrogen bond generates an S(6) ring. Molecules are linked via pairs of N—H⋯O hydrogen bonds, forming inversion dimers.

In the title compound, C 17 H 21 ClN 2 O 6 , the dihydropyrimidine ring adopts a flattened envelope conformation, with the sp 3 -hybridized C atom forming the flap. The dihedral angle between the least-squares planes of the benzene and dihydropyrimidine rings is 88.09 (6) . An Intramolecular C-HÁ Á ÁO hydrogen bond generates an S(6) ring. In the crystal, molecules are linked via pairs of N-HÁ Á ÁO hydrogen bonds, forming inversion dimers with an R 2 2 (8) ring motif, and the dimers are linked via further pairs of N-HÁ Á ÁO hydrogen bonds, forming R 2 2 (14) rings and chains of molecules along [111]. Pairs of inversion-related chains are linked via weak C-HÁ Á Á interactions.

Chemical context
Pyrimidine derivatives have been investigated extensively due to their great biological significance and as the main constituent of nucleic acids. Pyrimidines and their derivatives are considered to be important for drugs and agricultural chemicals. They are also found to exhibit remarkable pharmacological activities such as anti-cancer, anti-tumor, antiinflammatory and antifungal etc and are used widely as agrochemicals, pharmaceuticals, dyes, organic additives in electroplating of steel and in the polymerization process (Sharma et al., 2014;Vaisalini et al., 2012). Dihydropyrimidinones, the product of the Biginelli reaction, are also widely used in the pharmaceutical industry as calcium channel blockers and alpha-1 antagonists (Beena & Akelesh, 2012). Moreover, some bioactive alkaloids such as batzelladine B, containing the dihydropyrimidine unit, which has been isolated from marine sources, show anti-HIV activity (Asghari et al., 2011). Our interest in the preparation of pharmacologically active compounds led us to synthesize the title compound (I) and we report its crystal structure herein.

Supramolecular features
In the crystal, both N-H groups participate in intermolecular hydrogen-bonding associations (Table 1)  The molecular structure of the title compound, with displacement ellipsoids drawn at the 50% probability level. The dashed line indicates the intramolecular C10-H10AÁ Á ÁO1 hydrogen bond. Table 1 Hydrogen-bond geometry (Å , ).

Figure 3
Part of the crystal packing of the title compound, showing C-HÁ Á Á interactions and N-HÁ Á ÁO hydrogen bonds as dashed lines.

Figure 2
Partial crystal packing diagram for the title compound, showing the R 2 2 (8) and R 2 2 (14) ring motifs. Hydrogen bonds are shown as dashed lines.
features weak C-HÁ Á Á interactions between the methyl H atoms of the ethyl groups and the pyrimidine rings of inversion-related molecules.

Synthesis and crystallization
To an ethanolic solution of ethyl 4-chloroaceto acetate (2 ml, 0.012 mol), 2,3,4-trimethoxy benzaldehyde (2.4 g, 0.012 mol), and urea (2.25 g, 0.037 mol) were added followed by CeCl 3 Á7H 2 O (931 mg). The reaction mixture was taken in a round-bottom flask and refluxed for 2 h. Then the reaction mixture was cooled and poured into crushed ice taken in a beaker with constant stirring. The solid separated out was filtered, washed with ice-cold water and then recrystallized from hot ethanol to afford the product [yield: 92%; m.p. 425-427 K] as X-ray quality crystals.