5-Acetyl-4-(4-methoxyphenyl)-6-methyl-3,4-dihydropyrimidine-2(1H)-thione

In the title molecule, C14H16N2O2S, the heterocyclic ring adopts an envelope conformation with the plane through the five coplanar atoms making a dihedral angle of 88.99 (4)° with the benzene ring, which adopts an axial orientation. The thionyl, acetyl and methyl groups all have equatorial orientations. Intermolecular N—H⋯S, N—H⋯O, C—H⋯O and C—H⋯S hydrogen bonds are found in the crystal structure.

In the title molecule, C 14 H 16 N 2 O 2 S, the heterocyclic ring adopts an envelope conformation with the plane through the five coplanar atoms making a dihedral angle of 88.99 (4) with the benzene ring, which adopts an axial orientation. The thionyl, acetyl and methyl groups all have equatorial orientations. Intermolecular N-HÁ Á ÁS, N-HÁ Á ÁO, C-HÁ Á ÁO and C-HÁ Á ÁS hydrogen bonds are found in the crystal structure.

S1. Comment
As part of our investigations of dihydropyrimidine derivatives to compare their biological activity, we have undertaken the X-ray crystal structure analysis of the title compound. The crystal structures of three very closely related compounds have recently been reported [Anuradha et al., (2008[Anuradha et al., ( , 2009Chitra et al., (2009]; these studies have also reported their chemical and biological applications. In the title molecule, C 14 H 16 N 2 O 2 S, (Fig. 1), the heterocyclic ring adopts an envelope conformation with the plane through the five coplanar atoms (N1,C2,N3,C5,C6) making a dihedral angle of 88.99 (4)° with the benzene ring, which adopts an axial orientation. The thionyl, acetyl and methyl groups all have equatorial orientations. Intermolecular N1- 1 + y, z) and C61-H61B···S2(2 -x, 1 -y, 1 -z) hydrogen bonds are found in the crystal structure.

S2. Experimental
A solution of acetylacetone (1.001 g, 0.01 mol), 4-methoxybenzaldehyde (1.202 g, 0.01 mol) and thiourea (1.14 g, 0.015 mol) was heated under reflux in the presence of calcium fluoride (0.078 g, 0.001 mol) for 3 h (monitored by TLC). After completion of the reaction, the reaction mixture was cooled to room temperature and poured into crushed ice. The crude product containing also the catalyst was collected by filtration on a Buchner funnel. The mixture of the product and the catalyst was digested in methanol (40 ml). The undissolved catalyst was removed by filtration. The crude product was obtained by evaporation of the methanol and further purified by recrystallization from hot ethanol to afford the pure title compound. Yield 90% (1.2 g).

S3. Refinement
The two N-bound H atoms were located in a difference Fourier map and refined freely; N1-H1 = 0.87 (2) Å and N3-H3 = 0.85 (2) Å. The remaining H atoms were positioned geometrically and allowed to ride on their parent atoms, with C -H = 0.95 -1.00 Å ; U iso (H) = kU eq (C), where k = 1.5 for methyl and 1.2 for all other H atoms.

Special details
Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles 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.