Ethyl (E)-3-hydroxy-2-{N-[2-(thiophen-2-yl)ethenyl]carbamoyl}but-2-enoate

In the title compound, C13H15NO4S, there are two independent but conformationally similar molecules in the asymmetric unit, both having an E conformation of the side-chain C=C group. Intramolecular N—H⋯O and O—H⋯O hydrogen-bonding interactions are present in both molecules. In the crystal, one of the molecule types is linked through intermolecular hydroxy–ketone O—H⋯O interactions, forming one-dimensional chains extending along [010], whereas the other molecule type shows no associations.

In the title compound, C 13 H 15 NO 4 S, there are two independent but conformationally similar molecules in the asymmetric unit, both having an E conformation of the side-chain C C group. Intramolecular N-HÁ Á ÁO and O-HÁ Á ÁO hydrogenbonding interactions are present in both molecules. In the crystal, one of the molecule types is linked through intermolecular hydroxy-ketone O-HÁ Á ÁO interactions, forming one-dimensional chains extending along [010], whereas the other molecule type shows no associations.

D-HÁ
In the crystal, only one of the molecule types is linked through intermolecular hydroxyl O-H···O ketone interactions forming one-dimensional chain structures extending along (010) (Fig. 3), whereas the other molecule type is unassociated. The thiophene rings have normal hydrophobic contacts without any stacking interactions. For the structure of a similar compound, see Zhao & Huang (2012).

Experimental
To an ice-cooled solution of 3-(2-thienyl)acrylic acid (5.0 g, 32.5 mmol) in 70 ml of ethyl acetate was added triethylamine (4.3 g, 42.2 mmol) and diphenyl phosphorazidate (DPPA, 11.6 g, 42.2 mmol). The solution was stirred at room temperature for 4 h. The acyl azide product was washed by dilution with cold water. The organic layers were dried over MgSO 4 , and the solvent was removed under reduced pressure (< 318 K). The acyl azide was dissolved in 50 ml of benzene and heated under reflux until azide decomposition was complete. The reaction mixture was then cooled to 273 K and ethyl sodio-acetoacetate [prepared from ethyl acetoacetate (5.07 g, 39.0 mmol) and sodium hydride (1.1 g, 60% dispersion in oil, 45.5 mmol) in toluene (100 ml) at 273 K] was added. After warming to room temperature for 2 h, the mixture was quenched with saturated aqueous ammonium chloride solution, rinsed with brine, and dried over MgSO 4 .

Refinement
The amine hydrogen atom was located in a difference-Fourier map and refined freely. Other hydrogen atoms were positioned geometrically and refined using a riding model with O-H = 0.82 Å, C-H = 0.93 Å (CH), 0.96 Å (CH 3 ) or 0.97 Å (CH 2 ). Isotropic displacement parameters for these atoms were set to 1.2 (CH, CH 2 ) or 1.5 (OH, CH 3 ) times U eq of the parent atom.

Figure 1
The atom-numbering scheme of the first molecule in the asymmetric unit of the title compound, with displacement ellipsoids drawn at the 30% probability level. Hydrogen bonds are shown as dashed lines.

Figure 2
The atom-numbering scheme of the second molecule in the asymmetric unit of the title compound.

Ethyl (E)-3-hydroxy-2-{N-[2-(thiophen-2-yl)ethenyl]carbamoyl}but-2-enoate
Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'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 > 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.