Ethyl 4-(2,4-difluorophenyl)-6-methyl-2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate

In the title compound, C14H14F2N2O3, the dihydropyrimidinone ring adopts a flattened boat conformation. The difluorophenyl group is disordered over two orientations with occupancies of 0.544 (3) and 0.456 (3). The methoxycarbonyl group is disordered over two positions with occupancies of 0.580 (8) and 0.420 (8). In the crystal, molecules are linked into centrosymmetric dimers by paired N—H⋯O hydrogen bonds and the dimers are linked into a ribbon-like structure along [100] by further N—H⋯O hydrogen bonds.

In the title compound, C 14 H 14 F 2 N 2 O 3 , the dihydropyrimidinone ring adopts a flattened boat conformation. The difluorophenyl group is disordered over two orientations with occupancies of 0.544 (3) and 0.456 (3). The methoxycarbonyl group is disordered over two positions with occupancies of 0.580 (8) and 0.420 (8). In the crystal, molecules are linked into centrosymmetric dimers by paired N-HÁ Á ÁO hydrogen bonds and the dimers are linked into a ribbon-like structure along [100] by further N-HÁ Á ÁO hydrogen bonds.

Comment
Michael addition followed by aldol condensation known as the Robinson's annulation is synthetically a very useful reaction for the construction of six-membered cyclic compounds (Kalluraya and Rai, 2003). 3,4-Dihydro-pyrimidinones are compounds that have drawn wide-spread attention, due to their pharmaceutical applications (Atwal, 1990;Sadanandam et al., 1992). The common synthetic routes to these compounds generally involve multi-step transformation, which are essentially based on the Biginelli condensation methodology (Steele et al., 1998). These pyrimidinones are also associated with activities like calcium channel blocking (Manjula et al., 2004). We synthesized the title compound by means of Robinson's annulation employing the microwave technique, and its crystal structure is reported here.
The difluorophenyl group is disordered over two positions with occupancies of 0.544 (3) and 0.456 (3). The caboxylate methyl group is also disordered over two positions with occupancies of 0.580 (8) and 0.420 (8).
In the crystal structure, the molecules are linked into centrosymmetric dimers by means of paired N-H···O hydrogen bonds ( Table 1). The dimers are linked into a chain along the [100] again by N-H···O hydrogen bonds (Fig. 2).

Experimental
A mixture of 2,4-difluoro benzaldehyde (0.01 mol), ethyl acetoacetate (0.015 mol), thiourea (0.01 mol) and conc. H 2 SO 4 (2 drops) in absolute alcohol (10 ml) taken in a beaker (100 ml) was zapped inside a microwave oven for 3 min at 160 Watt (i.e. 25% MW power). The reaction mixture was then allowed to stand at room temperature and the product formed was filtered, washed with ethanol followed by water and dried. Further purification was done by recrystallisation from ethanol.
Single crystals suitable for X-ray analysis were obtained from ethanol by slow evaporation.

Refinement
Atoms H1N1 and H1N2 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 U iso (H) = 1.2-1.5 U eq (C). A rotating-group model was applied for the methyl group. The difluorophenyl group is disordered over two positions with occupancies of 0.544 (3) and 0.456 (3). The caboxylate methyl group is also disordered over two positions with occupancies of 0.580 (8) and 0.420 (8). For the disordered difluorophenyl group, the same U ij parameters were used for atom pairs F1A/F1B, C1A/C1B, and C5A/C5B, and all disordered atoms were subjected to a rigid bond restraint. Fig. 1. The molecular structure of the title compound, with atom labels and 50% probability displacement ellipsoids for non-H atoms. All disorder components are shown. Ethyl 4-(2,4-difluorophenyl)-6-methyl-2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cyrosystems 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 > 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.  (7) 0.0020 (7)  C10 0.0144 (9) 0.0250 (10) 0.0159 (8) 0.0081 (7) 0.0043 (7) 0.0012 (7)  supplementary materials sup-9