2-[7-(3,5-Dibromo-2-hydroxyphenyl)-6-ethoxycarbonyl-2-oxo-5H-2,3,6,7-tetrahydrothiopyrano[2,3-d][1,3]thiazol-6-yl]acetic acid ethanol monosolvate

The title compound, C17H15Br2NO6S2·C2H5OH, is the esterification reaction product of 2-(8,10-dibromo-2,6-dioxo-3,5,5a,11b-tetrahydro-2H,6H-chromeno[4′,3′:4,5]thiopyrano[2,3-d]thiazol-5a-yl)acetic acid. Cleavage of the lactone ring and formation of ethoxycarbonyl and hydroxy groups from its structural elements were observed. On the other hand, the carboxymethyl group was not esterified. The H atom and carboxymethyl group, both at stereogenic centres, show a cis conformation. The six-membered dihydrothiopyran ring adopts a half-chair conformation. All NH and OH groups participate in the three-dimensional hydrogen-bond network, which is additionally strengthened by C—H⋯O and C—H⋯S interactions. Intramolecular O—H⋯Br and C—H⋯O interactions also occur.

The molecular structure of compound (I) and the atom-labelling scheme is illustrated in Fig. 1.
The X-ray analysis showed that the crystal exists as ethanolic solvate. The asymmetric part of the unit cell contains one molecule of the compound (I) (solute) and one molecule of ethanol (solvent).
The carboxymethyl and ethoxycarbonyl groups at C7 atom of dihydrothiopyran ring are in an axial and equatorial positions, respectively, while the 3,4-dibromo-2-hydroxyphenyl substituent at C8 atom is in a pseudoaxial position.
The planar carboxymethyl and phenyl groups are approximately perpendicular to the least squares plane of the dihydrothiopyran ring; the dihedral angles are 83.10 (6) and 86.47 (6)

Refinement
Except for the amide and hydroxy H atoms which were refined freely the remaining H atoms were positioned into the idealized positions and were refined within the riding model approximation: C methyl -H = 0.96 Å, C methylene -H = 0.97 Å, C methine -H = 0.98 Å, C(sp 2 )-H = 0.93 Å; U iso (H) = 1.2U eq (C) or 1.5U eq (C) for methyl H. The methyl groups were refined as rigid groups which were allowed to rotate. The largest peaks and holes in the ΔF Fourier map are within 1.0 Å of the Br1 and Br2 atom sites.

Figure 2
The hydrogen bonding in the title crystal structure. Symmetry codes: (i) 1.5-x, -1/2+y, 0.5-z; (ii) 1-x, -y, 1-z; (iii) 1.5-x, 1/2+y, 1.5-z. H atoms not involved in hydrogen bonds have been ommitted for clarity.  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.