Crystal structure of 2-acetyl-5-(3,4-dimethoxyphenyl)-6-ethoxycarbonyl-3,7-dimethyl-5H-thiazolo[3,2-a]pyrimidin-8-ium chloride

The title molecular salt, C21H25N2O5S+·Cl−, crystallizes with two ion pairs in the asymmetric unit. The cations have similar conformations (r.m.s. overlay fit = 0.40 Å), with one of them showing disorder of the terminal methyl group of the ester in a 0.72 (2):0.28 (2) ratio. In the first cation, the 3,4-dimethoxy-substituted phenyl ring subtends a dihedral angle of 88.38 (7)° with the pyrimidine ring and 6.79 (8)° with the thiazole ring. The equivalent data for the second cation are 89.97 (3) and 6.42 (7)°, respectively. The pyrimidine ring adopts a sofa conformation in each cation. In the crystal, the components are linked by N—H⋯Cl hydrogen bonds, generating isolated ion pairs. The ion pairs are are linked by C—H⋯O interactions, generating a three-dimensional network. In addition, a weak C—H⋯π interaction is observed.

Cg3 is the centroid of the C9B-C14B ring. structure was confirmed by X-ray diffraction.
The molecular structure of the compound is shown in Fig. 1. The title compound, [C 21 H 25 N 2 O 5 S] + Cl -, crystallizes in the triclinic space group with two molecules in the asymmetric unit. In molecules A and B, the 3,4-dimethoxy substituted phenyl ring form dihedral angle of 88.38 (7)° / 89.97 (3)° with mean plane of the pyrimidine ring and 6.79 (8)° / 6.42 (7)° with thiazole ring respectively. The two values separated by / corresponds to the two molecules in the asymmetric unit.

S3. Refinement
The H atoms were placed at calculated positions in the riding-model approximation with C-H = 0.95° A, 1.00 ° A and 0.96 ° A for aromatic, methyne and methyl H-atoms respectively, with U iso (H) = 1.5U eq (C) for methyl H atoms and U iso (H) = 1.2Ueq(C) for other hydrogen atoms.

Figure 1
The molecular structure of the title compound with displacement ellipsoids drawn at the 50% probability level.   Unit-cell packing depicting the intermolecular C-H···π interactions with dotted lines.

2-Acetyl-5-(3,4-dimethoxyphenyl)-6-ethoxycarbonyl-3,7-dimethyl-5H-thiazolo[3,2-a]pyrimidin-8-ium chloride
Special details Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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.