Crystal Structure of Ethyl (2Z, 5R)-2-benzylidene-7-methyl-3-oxo-5-phenyl-2,3-dihydro-5H-[1,3] Thiazolo [3,2-a] Pyrimidine-6-carboxylate

The title compound, C23H20N2O3S, (I), crystallizes in the orthorhombic space group, Pna 2(1), with cell parameters a = 18.7975(6), b = 12.5173(4), c = 8.4804(3) angstrom, Z = 4. The molecular structure consists of a central pyrimidine ring which is significantly puckered to assume a screw-boat conformation fused to a thiazole ring with benzyl, carboxylate, methyl, phenyl and oxy groups bonded around this fused-ring moiety. The dihedral angle between the mean planes of the thiazole, benzyl and phenyl groups and the mean plane of the pyrimidine ring is 6.1(4)degrees, 83.8(7)degrees and 6.8(4)degrees, respectively. The dihedral angle between the mean planes of the benzyl and phenyl rings is 88.3(5)degrees while between the mean planes of the phenyl and thiazole groups measures 12.6(6)degrees. In the absence of expected hydrogen bonding interactions, the crystal packing is influenced by a collective action of strong intramolecular C-H center dot center dot center dot S hydrogen bond interactions, close C-H center dot center dot center dot O intramolecular contacts and O-Cg pi-ring interactions. A DFT molecular orbital calculation gives support to these observations.