Ethyl 2-(2-acetoxybenzylidene)-7-methyl-3-oxo-5-phenyl-2,3-dihydro-5H-1,3-thiazolo[3,2-a]pyrimidine-6-carboxylate1

In the title molecule, C25H22N2O5S, the atoms of the thiazolopyrimidine ring system, with the exception of the phenyl-bearing C atom [deviation = 0.177 (2) Å], are essentially planar [r.m.s deviation = 0.100 (2) °] and the mean plane of these atoms forms dihedral angles of 89.86 (10) and 7.97 (8)° with the phenyl and benzene rings, respectively. In the crystal, co-operative C—H⋯O and C—H⋯π interactions lead to a supramolecular chain along the a axis. These chains are connected via π–π interactions [centroid–centroid = 3.7523 (13) Å].

In the title molecule, C 25 H 22 N 2 O 5 S, the atoms of the thiazolopyrimidine ring system, with the exception of the phenyl-bearing C atom [deviation = 0.177 (2) Å ], are essentially planar [r.m.s deviation = 0.100 (2) ] and the mean plane of these atoms forms dihedral angles of 89.86 (10) and 7.97 (8) with the phenyl and benzene rings, respectively. In the crystal, co-operative C-HÁ Á ÁO and C-HÁ Á Á interactions lead to a supramolecular chain along the a axis. These chains are connected viainteractions [centroid-centroid = 3.7523 (13) Å ].

Comment
The absolute stereochemistry at C2 stereocentre in fused dihydropyrimidine rings is a critical factor for their biological activity and provides an additional opportunity to study the effect of chirality on biological activities (Atwal et al., 1990;Kappe, 2000). The title compound, (I), exhibits anti-cancer (Adams et al., 2005) and anti-inflammatory activities (Winter et al., 1962). In continuation of our structural studies of these pharmacologically interesting thiazolo[3,2-a]pyrimidine derivatives, designed to ascertain the influence of substitution patterns upon crystal packing (Jotani & Baldaniya, 2007;Jotani et al., 2009), the synthesis and crystal structure of the title compound, (I), is described herein.
Allowing for the presence of distinct substituents, the molecular framework in (I) resembles closely those found in related derivatives (Jotani & Baldaniya, 2007;Jotani et al., 2009) The crystal structure is stabilised by a variety of weak intermolecular interactions. A supramolecular chain aligned along the a axis is formed through the agency of C-H···O and C-H···π interactions, Fig. 2 and Table 1. These are connected via π-π interactions formed between centrosymmetrically related C18-C23 rings [ring centroid(C18-C23)···ring Semi-empirical Quantum Chemical Calculations were performed with the MOPAC2009 program (Stewart, 2009) in order to optimize the experimental structure with the Austin Model 1 (AM1) approximation together with the restricted Hartree-Fock closed-shell wavefunction; minimisations were terminated at a r.m.s. gradient of less than 1.0 kJ mol -1 Å -1 .
The heat of formation was calculated to be -313.14 kJ mol -1 . The ionization potential, dipole moment and self consistency field (SCF) factor were calculated as 8.633 eV, 3.880 Debye, and 121, respectively.

Refinement
The C-bound H atoms were geometrically placed (C-H = 0.93-0.98 Å) and refined as riding with U iso (H) = 1.2-1.5U eq (parent atom). Fig. 1. The molecular structure of (I) showing the atom-labelling scheme and displacement ellipsoids at the 35% probability level.  Ethyl 2-(2-acetoxybenzylidene)-7-methyl-3-oxo-5-phenyl-2,3-dihydro-5H-1,3-thiazolo[3,2-a]pyrimidine-6carboxylate 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 Rfactors(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.