Methyl 2-(2-bromobenzylidene)-5-(4-hydroxyphenyl)-7-methyl-3-oxo-2,3-dihydro-5H-1,3-thiazolo[3,2-a]pyrimidine-6-carboxylate

In the title compound, C22H17BrN2O4S, the central dihydropyrimidine ring, with a chiral C atom, is significantly puckered and adopts a half-chair conformation with the chiral C atom displaced from the mean plane of the remaining ring atoms by 0.305 (6) Å. The hydroxy-phenyl ring is positioned axially to the pyrimidine ring and almost bisects it, the dihedral angle between the mean-planes of the two rings being 89.78 (12)°. The methoxycarbonyl group is disordered over two sites with an occupancy ratio of 0.568 (5):0.432 (5), resulting in a major and a minor conformer. In the crystal, O—H⋯N and C—H⋯S interactions result in sheets along the c axis. The supramolecular assembly is stabilized by π–π stacking interactions between the 2-bromobenzylidene and thiazolopyrimidine rings [centroid–centroid distance = 3.632 (1) Å]. In addition, C—H⋯π interactions are also observed in the crystal structure.

NSB is thankful to the University Grants Commission (UGC), India, for financial assistance.

H. Nagarajaiah, Nikhath Fathima and Noor Shahina Begum Comment
The title compound is a representative of thiazolopyrimidine derivatives, which have recently emerged as target molecules due to their therapeutic and medicinal properties (Kappe, 2000) such as anti-inflammatory and antinociceptive activities (Ozair et al. 2010) in addition to being calcium channel blockers.
In the title molecule ( Fig. 1), the 4-hydroxy-phenyl group adopts a psuedo synperiplanar conformation with respect to C5-H5 bond. The central pyrimidine ring with a chiral C5 atom is significantly puckered and adopts a half chair conformation with C5 displaced from the mean plane of the remaining ring atoms (C6/C7/C9//N2/N1) by 0.305 (6) Å.
The hydroxy-phenyl ring is positioned axially to the pyrimidine ring and almost bisects it with a dihedral angle between the mean-planes of the two rings being 89.78 (12)°. The methoxycarbonyl group in the title compound is disordered in which the carbon atoms C8, C4 and the oxygen atoms O2 and O3 are located over two sites (C8A/C8B,C4A/C4B, O2A/O2B and O3A/O3B) with site occupancy ratio 0.568 (5):0.432 (5) resulting in a major and a minor conformers. The crystal structure is primarily stabilized by intermolecular O4-H4···N2 and C4B-H4B1···S1 interactions which result in two dimensional sheets along the c-axis (Fig. 2). The molecular packing is further stabilized by π-π stacking interactions between the thiazolopyrimidine and 2-bromo-benzylidene rings. The C3···C21 (x -1, y, z -1) disposed at a distance of 3.632 (1) Å. In addition C1-H1···Cg1 interactions (Cg1 being the centroid of the benzene ring C10-C15, Table 1) are also observed. The bond lengths and angles in the title molecule are in close agreement with the corresponding bond lengths and angles reported in a similar compound (Nagarajaiah & Begum, 2011).

Refinement
The H atoms were placed at calculated positions in the riding model approximation with O-H = 0.82 Å and C-H = 0.93, 0.96 and 0.98 Å for aryl, methyl and methyne H-atoms respectively, with U iso (H) = 1.5U eq (C) for methyl H atoms and 1.2U eq (C/O) for other H atom.

Figure 1
The molecular structure of the title compound with the atom numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. H atoms are presented as small spheres of arbitrary radius.  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 1.04 e Å −3 Δρ min = −0.87 e Å −3 Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'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.

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