Ethyl (2E)-2-(2H-1,3-benzodioxol-5-ylmethylidene)-4-chloro-3-oxobutanoate

In the title compound, C14H13ClO5, the five-membered ring is in an envelope conformation with the methylene C-atom being the flap. The conformation about the C=C double bond [1.341 (2) Å] is E. The chloropropan-2-one residue is approximately orthogonal to the remaining molecule [dihedral angle = 88.03 (6)°]. In the crystal, the molecules associate via C—H⋯O interactions, involving both carbonyl-O atoms, giving rise to an undulating two-dimensional array in the ac plane.

In the title compound, C 14 H 13 ClO 5 , the five-membered ring is in an envelope conformation with the methylene C-atom being the flap. The conformation about the C C double bond [1.341 (2) Å ] is E. The chloropropan-2-one residue is approximately orthogonal to the remaining molecule [dihedral angle = 88.03 (6) ]. In the crystal, the molecules associate via C-HÁ Á ÁO interactions, involving both carbonyl-O atoms, giving rise to an undulating two-dimensional array in the ac plane.

Related literature
For background to the study, see: Rodrigues et al. (2004). For ring conformational analysis, see: Cremer & Pople (1975

Experimental
The title compound, (I), was prepared by means of a Knoevenagel condensation reaction between ethyl 4-chloroacetoacetate and piperonal. Morpholine (17.4 mg, 0.2 mmol), glacial acetic acid (12.0 mg, 0.2 mmol) and piperonal (300 mg, 2 mmol) were added to [Bmim][NTf 2 ] (1 ml) in a 10 ml round-bottom flask. The mixture was stirred for 10 min., and then ethyl 4-chloroacetoacetate (395 mg, 2.4 mmol) and 4 Å molecular sieves (360 mg) were added to reaction mixture. After 1.5 h, the ionic liquid layer was extracted with diethyl ether (3 x 5 ml), the ether was evaporated to afford a mixture of E and Z isomers that were separated by column chromatography (hexane/ethyl acetate, gradient from pure hexane to 95% hexane/5% ethyl acetate). The crystallized isomer, obtained by slow evaporation from a dichloromethane/hexane mixture, was shown by crystallography to be the E isomer; M.pt. 367.1-367.4 K.
supplementary materials sup-2 Refinement Carbon-bound H-atoms were placed in calculated positions (C-H 0.93 to 0.97 Å) and were included in the refinement in the riding model approximation, with U iso (H) = 1.2U eq (C) and 1.5U eq (methyl-C). Fig. 1. The molecular structure of compound (I) showing the atom-labelling scheme and displacement ellipsoids at the 50% probability level.

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 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 Rfactors(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.