ORIGINAL PAPER 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 Mukesh M. Jotani Bharat B. Baldaniya Jerry P. Jasinski Received: 30 December 2008 / Accepted: 7 June 2009 / Published online: 24 June 2009 Ó Springer Science+Business Media, LLC 2009 Abstract The title compound, C 23 H 20 N 2 O 3 S, (I), crys- tallizes in the orthorhombic space group, Pna 2 1 , with cell parameters a = 18.7975(6), b = 12.5173(4), c = 8.4804(3) A ˚ , 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 bon- ded 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)°, 83.8(7)° and 6.8(4)°, respectively. The dihedral angle between the mean planes of the benzyl and phenyl rings is 88.3(5)° while between the mean planes of the phenyl and thiazole groups measures 12.6(6)°. In the absence of expected hydrogen bonding interactions, the crystal packing is influenced by a collective action of strong intramolecular C–HÁÁÁS hydrogen bond interactions, close C–HÁÁÁO intramolecular contacts and O–Cg p-ring interactions. A DFT molecular orbital calculation gives support to these observations. Keywords Thiazole Á Pyrimidine Á Ring puckering Á Benzene Á DFT calculations Introduction The remarkable biological activities of fused pyrimidines which give rise to antiviral, anticancer, anti-inflammatory and antihypertensive actions [1, 2], continue to bring this class of heterocyclic compounds to the forefront of interest and study. The title thiazolo[3,2-a]pyrimidine compound, (I), exhibits both anticancer and anti-inflammatory activity. In support of these observations, an anticancer drug screen has been carried out using a diverse panel of cultured human tumor cell lines [3]. Anti-inflammatory activity has been determined by examination of inhibition by the Carageena-induced rat paw edema method [4]. In view of these observations and in the continuation of our recent studies on thiazolo[3,2-a]pyrimidine compounds [5–8], we have been investigating the influence of different substituent’s on the structural parameters of these com- pounds as well as crystal packing when relating these properties to the biological effects of these compounds. We report herethe crystal structure of the title compound, C 23 H 20 N 2 O 3 S, (I). Synthesis 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 A mixture of ethyl 6-methyl-4-phenyl-2-thioxo-1,2,3,4- tetrahydropyrimidine-5-carboxylate (0.01 mol), chloroace- tic acid (0.01 mol), fused sodium acetate (6 g) in glacial acetic acid (25 mL), acetic anhydride (10 mL) and benz- aldehyde (0.01 mol) was refluxed for 3 h. The reaction mixture was cooled and poured into cold water. The resulting solid was collected and crystallized from metha- nol to obtain the final product (86% yield, mp 443 K). The compound was recrystallized by slow evaporation of a M. M. Jotani Department of Physics, Bhavan’s Sheth R.A. College of Science, Khanpur, Ahmedabad, Gujarat 380 001, India B. B. Baldaniya Department of Chemistry, M.G. Science Institute, Navrangpura, Ahmedabad, Gujarat 380 009, India J. P. Jasinski (&) Department of Chemistry, Keene State College, 229 Main Street, Keene, NH 03435-2001, USA e-mail: jjasinski@keene.edu 123 J Chem Crystallogr (2009) 39:898–901 DOI 10.1007/s10870-009-9587-z