Ethyl 3-acetyl-4-(3-methoxyphenyl)-6-methyl-2-sulfanylidene-1,2,3,4-tetrahydropyrimidine-5-carboxylate

In the title compound, C17H20N2O4S, the aryl ring is positioned perpendicular to the dihydropyrimidine ring, the dihedral angle between the ring planes being 77.48 (9)°. The carboxylate and methyl groups are in a cis conformation with respect to the C=C bond. The dihydropyrimidine ring adopts a twist-boat conformation. The crystal structure is stabilized by N—H⋯O and C—H⋯O interactions, the former resulting in molecular chains along the b axis and the latter forming inversion dimers.

In the title compound, C 17 H 20 N 2 O 4 S, the aryl ring is positioned perpendicular to the dihydropyrimidine ring, the dihedral angle between the ring planes being 77.48 (9) . The carboxylate and methyl groups are in a cis conformation with respect to the C C bond. The dihydropyrimidine ring adopts a twist-boat conformation. The crystal structure is stabilized by N-HÁ Á ÁO and C-HÁ Á ÁO interactions, the former resulting in molecular chains along the b axis and the latter forming inversion dimers.
NSB is thankful to the University Grants Commission (UGC), India, for financial assistance.

Nikhath Fathima, H Nagarajaiah and Noor Shahina Begum Comment
Dihydropyrimidines have remarkable potency with antiviral, antitumor, antibacterial and anti-inflammatory activities, and are used as antihypertensive agents and calcium channel modulators (Kappe, 2000). In the structure of the title compound, the aryl ring substituted to chiral carbon atom (C4) is positioned axially to the dihydropyrimidine ring, whereas the carboxylate, methyl, acetyl and the thioxo groups are attached on the either sides of the ring. The dihedral angle between the planes of the aryl and dihydropyrimidine rings is 77.48 (9)°. The exocyclic ester at C5 adopts a cis orientation with respect to C5═C6 double bond. The central dihydropyrimidine ring is significantly puckered, assuming a conformation of twisted boat with the atoms N1 and C1 displaced from the mean plane of the remaining ring atoms Experimental 4-(3-Methoxy-phenyl)-6-methyl-2-thioxo-1,2,3,4-tetrahydro-pyrimidine-5 carboxylic acid ethyl ester (3.06 g, 10 mmol) was mixed with acetic anhydride (20 ml) and refluxed for about 4 h. The reaction mixture was cooled and diluted by addition of water (20 ml). The solid separated, washed with water, filtered and dried (Yield: 1.92 g, 85% and mp 430-432 K). Pale yellow crystals of the title compound were obtained for diffraction by slow evaporation from a solution in chloroform.

Refinement
The H atoms were placed at calculated positions in the riding model approximation with N-H = 0.86Å, C-H = 0.93, 0.96, 0.97 and 0.98 Å for aryl, methyl, methylene and methyne H-atoms respectively, with U iso (H) = 1.5U eq (C) for methyl H atoms and U iso (H) = 1.2U eq (N/C).

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.