(Z)-Ethyl 3-(2,4,6-trimethylanilino)but-2-enoate

The title compound, C15H21NO2, was obtained by the reaction of acetoacetate with 2,4,6-trimethylaniline using Mexican bentonitic clay as a catalyst. It crystallizes in the enamine form. The β-enamino ester residue is almost perpendicular to the aromatic ring [dihedral angle = 88.10 (6)°]. The molecular conformation is stabilized by a strong intramolecular N—H⋯O hydrogen bond. In addition, the N—H group forms a weak intermolecular N—H⋯O hydrogen bond linking the molecules into centrosymmetric dimers.

The title compound, C 15 H 21 NO 2 , was obtained by the reaction of acetoacetate with 2,4,6-trimethylaniline using Mexican bentonitic clay as a catalyst. It crystallizes in the enamine form. The -enamino ester residue is almost perpendicular to the aromatic ring [dihedral angle = 88.10 (6) ]. The molecular conformation is stabilized by a strong intramolecular N-HÁ Á ÁO hydrogen bond. In addition, the N-H group forms a weak intermolecular N-HÁ Á ÁO hydrogen bond linking the molecules into centrosymmetric dimers.

Experimental
The enamino esters are gaining increased interest, which are known as important intermediates for the synthesis of natural products (Marchand et al, 1994). The β-enamino esters are useful in synthesis of pharmaceuticals and bioactive heterocycles (Spivey et al., 2003) and as precursors for the preparation of antibacterial, anticonvulsant (Michael et al., 2001), anti-inflamatory and antitumour agents. The functionalization of these compounds by the introduction of different substituents on the nitrogen atom, the α-carbon and β-carbonylic carbon atoms has been studied (Braibante et al., 2002).
The molecular structure and the atomic numbering scheme is shown in Fig. 1. The trimethylyphenyl substituent is almost perpendicular to the β-enaminoester function forming a dihedral angle of 88.10 (6)°.

S3. Refinement
H atom on amine group was found in Fourier map and its coordinates were refined with U iso (H) = 1.2 U eq (N). H atoms bonded to C atoms were placed in geometrically idealized positions [C-H = 0.97 Å (for CH 2 ) and 0.96 Å (for CH 3 )] and refined using a riding model with U iso (H) = 1.2 U eq (C) or 1.5 U eq C(methyl).  The Molecular structure with the atom numbering scheme. Displacement ellipsoids are drawn at the 40% probability level. H atoms bonded to C omitted. The intramolecular hydrogen bond is shown as a dashed line.

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.