Crystal structure of ethyl 4-(2-fluorophenyl)-6-methyl-2-sulfanylidene-1,2,3,4-tetrahydropyrimidine-5-carboxylate

The title compound, C14H15FN2O2S, crystallizes with two molecules in the asymmetric unit. In each molecule, the pyrimidine ring adopts a sofa conformation with the sp 3-hybridized C atom forming the flap and the fluoro-substituted ring in an axial position. In the crystal, molecules are linked via N—H⋯S hydrogen bonds, forming chains of R 2 2(8) rings along [100]. In one independent molecule, an intramolecular C—H⋯O hydrogen bond is observed.


S2. Experimental
The title compound was synthesized by the reaction of 2-fluorobenzaldehyde (1.24 g, 10 mmol), ethylacetoacetate (1.52 g, 12 mmol) and thiourea (1.14 g, 15 mmol) in 15 ml ethanol was refluxed for 6 h in the presence of concentrated hydrochloric acid as a catalyst. The reaction was monitored with TLC and the reaction medium was quenched in ice cold water.
The precipitate obtained was filtered and dried. The compound was recrystallized from ethanol solvent by slow evaporation method, yielding colorless blocks suitable for X-ray diffraction studies (yield 76%; m.p. 485 K).

S3. Refinement
The H atoms were placed in calculated positions in a riding-model approximation with N-H = 0.86° A; C-H = 0.93° A, 0.96 ° A and 0.97 ° A for aromatic, methyl and methylene H-atoms respectively, with U iso (H) = 1.5U eq (C) for methyl H atoms and U iso (H) = 1.2U eq (C) for other hydrogen atoms.

Figure 1
The asymmetric unit of the title compound with displacement ellipsoids drawn at the 50% probability level. H atoms are presented as small spheres of arbitrary radius.

Figure 2
Part of the crystal structure with hydrogen bonds shown as dashed lines.  Special details Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'s 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 > 2σ(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.