rac-Ethyl 3-(3-bromo-2-thienyl)-2-oxo-6-(4-propoxyphenyl)cyclohex-3-ene-1-carboxylate

The racemic title compound, C22H23BrO4S, crystallizes with two molecules in the asymmetric unit. The dihedral angles between the thiophene and phenyl rings are 71.64 (17) and 73.41 (17)°.

The racemic title compound, C 22 H 23 BrO 4 S, crystallizes with two molecules in the asymmetric unit. The dihedral angles between the thiophene and phenyl rings are 71.64 (17) and 73.41 (17) .

Experimental
MTS thanks the University of Mysore for research facilities. The Swedish Research Council (VR) is acknowledged for providing funding for the single-crystal diffractometer.

S1. Comment
Chalcones and the corresponding heterocyclic analogues are valuable intermediates in organic synthesis (Dhar, 1981) and exhibit a multitude of biological activities (Dimmock et al. 1999). From a chemical point of view, an important feature of chalcones and their heteroanalogues is the ability to act as activated unsaturated systems in conjugated addition reactions of carbanions in the presence of basic catalysts (House, 1972). This type of reaction may be exploited with the view of obtaining highly functionalized cyclohexene derivatives (Tabba et al.,1995) but is more commonly used for the preparation of 3,5-diaryl-6-carbethoxycyclohexanones via Michael addition of ethylacetoacetate. The mentioned cyclohexenones are efficient synthons in building spiranic compounds (Padmavathi et al.,2001) or intermediates in the synthesis of benzisoxazoles or carbazolederivatives (Padmavathi et al., 1999(Padmavathi et al., , 2000(Padmavathi et al., , 2001a. In view of the importance of these derivatives, a new derivative rac-ethyl-3-(3-bromo-2-thienyl)-6-(4-propoxyphenyl)-2-oxocyclohex-3-ene-1carboxylate, C 22 H 23 BrO 4 S was prepared and the crystal structure is reported here.
The compound is prepared by the cyclocondensation of ethyl acetoacetate with chalcone which leads to the generation of two chiral centers at C1 and C6 in the structure of cyclohexanone (I). As the reaction is not stereoselective, both configurations of the chiral carbon atoms are expected to be obtained in the synthesiszed cyclohexanone(I), which would result in a mixture of diastereomers. No attempt to separate the diastereomeric I has been undertaken and the crystals were grown from the mixture after recrystallization.

S3. Refinement
Hydrogen atoms were placed at calculated positions and refined riding on the respective carrier atom. Attempts to improve the structure model using a split position for C43 and C44 resulted in an unstable refinement. Attempts to acquire data at low temperature resulted in severe deterioration of the crystal quality.  The two molecules in the asymmetric unit. Displacement ellipsoids are drawn at the 50% probability level.

rac-Ethyl 3-(3-bromo-2-thienyl)-2-oxo-6-(4-propoxyphenyl)cyclohex-3-ene-1-carboxylate
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.