Crystal structure of ethyl 4-(2,4-dichlorophenyl)-2-methyl-4H-benzo[4,5]thiazolo[3,2-a]pyrimidine-3-carboxylate

In the title compound, C20H16Cl2N2O2S, the pyrimidine ring has a screw-boat conformation. The attached dichlorophenyl ring is twisted at an angle of 89.29 (13)° with respect to the pyrimidine ring mean plane. The benzothiazole group is approximately planar (r.m.s. deviation = 0.008 Å) and inclined to the pyrimidine ring mean plane by 3.04 (10)°. The carboxylate group assumes an extended conformation with respect to the pyrimidine ring, which can be seen from the O=C—O—C torsion angle of 3.2 (4) °. In the crystal, molecules are linked via C—H⋯O and C—H⋯N hydrogen bonds, forming slabs lying parallel to (100).

The molecular structure of the title compound is shown in Fig. 1 respect to the pyrimidine ring mean plane. The carboxylate group assumes an extended conformation with respect to the pyrimidine ring, which can be seen from the torsion angle O24-C23-O25-C26 = 3.2 (4) °.
In the crystal, molecules are linked via C-H···O and C-H···N hydrogen bonds forming slabs lying parallel to (100); see Table 1 and Fig. 2.

S2. Synthesis and crystallization
A mixture of 2,4-dichloro benzaldehyde was treated with ethyl acetoacetate and 2-aminobenzothiazole in the presence of ammonium acetate in ethanol. The mixture was gently warmed in a water bath at 353 K until the colour changed and it was then kept aside overnight at room temperature. The completion of reaction was monitored by TLC. The solid obtained was separated and purified by means of column chromatography using hexane and ethyl acetate as eluent. The sample was recrystallized using a 1:1 mixture of ethanol and THF, yielding yellow block-like crystals.

S3. Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. H atoms were positioned geometrically and allowed to ride on their parent atoms: C-H = 0.93-0.98 Å with U iso (H) = 1.5U eq (C) for methyl H atoms and 1.2U eq (C) for other H atoms.

Figure 1
The molecular structure of the title compound, with atom labelling. Displacement ellipsoids are drawn at the 30% probability level.

Figure 2
The crystal packing of the molecules viewed down the c axis.  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 > σ(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.