Ethyl (Z)-3-(4-methylanilino)-2-[(4-methylphenyl)carbamoyl]prop-2-enoate

The title compound, C20H22N2O3, is a secondary amine featuring an amide and an ester functionality in connection with a Michael system. The conformation about the C=C bond is E. Intramolecular N—H⋯O hydrogen bonds occur. In the crystal, C—H⋯O contacts connect the molecules into chains along the b-axis direction.

In the crystal, intramolecular N-H···O bonds involving all secondary amine groups and double bonded oxygen atoms are observed. In addition, intermolecular C-H···O contacts whose range falls slightly below the sum of van-der-Waals radii of the atoms participating are present. The latter contacts are supported by hydrogen atoms on the phenyl group that is bonded to the amide-type nitrogen atom and exclusively have ketonic oxygen atoms as acceptors. In terms of graph-set analysis (Etter et al., 1990;Bernstein et al., 1995), the descriptor for these contacts is S(6)S(6)R 2 2 (14)R 2 2 (18) on the unary level. Metrical parameters as well as information about the symmetry of these contacts are summarized in Table 1. In total, the molecules are connected to chains along the crystallographic b axis. The shortest intercentroid distance between two aromatic systems was measured at 4.5754 (9) Å and is observed between the two different aromatic moieties in neighbouring molecules (Fig 2).
The packing of the title compound in the crystal structure is shown in Figure 3.

Experimental
A mixture of diethyl-{[(4-methylphenyl)amino]methylidene}propanedioate (1.0 g, 0.0036 mol) and 4-methylaniline (0.19 g, 0.0018 mol) in dowtherm (10 ml) was stirred at 150 °C for 2 h. The reaction mixture was then cooled to 25 °C and stirred in n-hexane (20 ml) for 10 min. The solid product obtained was filtered, dried and further purified by column chromatography using petrol ether and ethyl acetate (v:v = 5:5) as the eluent to get a white solid. Crystals were grown by slow evaporation of a dilute ethanol solution at room temperature, yield: 0.52 g (42.6%).

Refinement
Carbon-bound H atoms were placed in calculated positions (C-H = 0.95 Å for aromatic and vinylic carbon atoms, C-H = 0.99 Å for the methylene group, and C-H = 0.98 Å for the methyl groups) and were included in the refinement in the riding model approximation, with U iso (H) set to 1.2 or 1.5U eq (C). The H atoms of the methyl groups were allowed to supplementary materials rotate with a fixed angle around the C-C bond to best fit the experimental electron density [HFIX 137 in the SHELX program suite (Sheldrick, 2008), with U iso (H) set to 1.5U eq (C)]. Both nitrogen-bound H atoms were located on a difference Fourier map and refined freely.

Figure 1
The molecular structure of the title compound, with atom labels and anisotropic displacement ellipsoids (drawn at 50% probability level).