Ethyl 2-[(Z)-3-chlorobenzylidene]-7-methyl-3-oxo-5-phenyl-2,3-dihydro-5H-1,3-thiazolo[3,2-a]pyrimidine-6-carboxylate

In the title compound, C23H19ClN2O3S, the central pyrimidine ring is significantly puckered, assuming almost a screw boat conformation. In addition to the usual intermolecular C—H⋯O hydrogen bonding, short intramolecular C—H⋯S contacts and π–π stacking interactions [centroid–centroid distance = 3.762 (2) Å] contribute to the crystal packing.

The anticancer drug screen is carried out using a diverse panel of cultured human tumor cell lines (Monks et al., 1991).
The anti-inflammatory activity is determined by inhibition in the Carageena-induced rat paw edema method (Winter et al., 1962). In view of these properties and to study the effect of chlorine substituent at different positions of benzene ring on crystal packing, the crystal structure of I has been determined.
The crystal structure of I is also have an intermolecular C-H···O interaction ( Fig. 2 and Table) similar to earlier reported ortho-and para-substituted compounds (Jotani & Baldaniya, 2006, 2007. In the structure a carbon C23 atom of C18-C23 benzene ring participates in the C-H···O interaction that forms R 2 2 (14) graph-set motif (Bernstein et al., 1995), where as in ortho-and para-substituted chlorine derivatives, the interaction is due to C14 atom of C11-C16 benzene ring. This may be the different symmetry of the crystal system as the title compound I crystallizes in triclinic system where as the previous two structures were crystallized in monoclinic space group. A PLATON analysis (Spek, 2003) of I indicated that a weak intramolecular C-H···S hydrogen bond ( Fig. 1 and Table) forms a pseudo-six-membered ring of S(6) graph-set motif (Bernstein et al., 1995) also help to consolidate the crystal packing. There is a comparatively weak π-π stacking interaction between the C18-C23 benzene rings with symmetry codes: (x, y, z) and (1-x, 1-y, -z); their centroids are separated by 3.762 (2)Å and the rings have a slippage of 1.523Å (Fig. 3).

Refinement
H atoms were placed in idealized positions (C-H = 0.93-0.98Å) and constrained to ride on their parent atoms with U iso (H) = 1.5U eq (C) for methyl H atoms and 1.2U eq (C) for other H atoms. Fig. 1. The molecular structure of I with the atom numbering scheme. Displacement ellipsoids are drawn at 50% probability level. H atoms are presented as a small spheres of arbitrary radius. The C-H···S intramolecular hydrogen bond is indicated by dashed line.    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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq S1 0.30130 (