Ethyl 4-[3,5-bis(trifluoromethyl)phenyl]-6-methyl-2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate

In the title compound, C16H14F6N2O3, the dihydropyrimidinone ring adopts an envelope conformation. In the crystal, molecules are linked by N—H⋯O and C—H⋯O hydrogen bonds into a ribbon-like structure along the b axis. In the ribbon, a pair of bifurcated acceptor N—H⋯O and C—H⋯O bonds generate an R 2 1(6) ring motif. Adjacent ribbons are linked via C—H⋯F hydrogen bonds.

In the title compound, C 16 H 14 F 6 N 2 O 3 , the dihydropyrimidinone ring adopts an envelope conformation. In the crystal, molecules are linked by N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds into a ribbon-like structure along the b axis. In the ribbon, a pair of bifurcated acceptor N-HÁ Á ÁO and C-HÁ Á ÁO bonds generate an R 2 1 (6) ring motif. Adjacent ribbons are linked via C-HÁ Á ÁF hydrogen bonds.
The common synthetic routes to these compounds generally involve multi-step transformations that 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 report here the crystal structure of the title compound which was synthesized by means of Robinson's annulation employing microwave technique.
H 2 SO 4 (2 drops) in absolute alcohol (10 ml) taken in a beaker (100 ml) was zapped inside a MW oven for a duration of 3 minutes (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 recrystallization from ethanol. Single crystals suitable for X-ray analysis were obtained by slow evaporation of an ethanol solution.

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 = 0.95-1.00 Å and U iso (H) = 1.2 or 1.5U eq (C). A rotating-group model was applied for the methyl groups. Some of the F atoms show elongated ellipsoids indicating disorder. Attempts to refine a disorder model resulted in large s.u's on occupancy factors and almost the same positional parameters for corres-supplementary materials sup-2 ponding F atoms in the major and minor disorder components. Hence the original model was used with the U ij parameters of all F atoms restrained to an approximate isotropic behaviour. Fig. 1. The molecular structure of the title compound, showing 50% probability displacement ellipsoids and the atom-numbering scheme.  Ethyl 4-[3,5-bis(trifluoromethyl)phenyl]-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 110.0 (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.