Crystal structure of ethyl 5-acetyl-2-{[(dimethylamino)methylidene]amino}-4-methylthiophene-3-carboxylate

In the title thiophene derivative, C13H18N2O3S, the dihedral angles between the thiophene ring and the [(dimethylamino)methylidene]amino side chain (r.m.s. deviation = 0.009 Å) and the –CO2 ester group are 3.01 (16) and 59.9 (3)°, respectively. In the crystal, inversion dimers linked by pairs of C—H⋯O hydrogen bonds generate R 2 2(16) loops. The dimers are linked by another weak C—H⋯O interaction, forming chains along [001]. In addition, weak C—H⋯π interactions are observed, which link the chains into (001) layers.


Related literature
For background to the applications of thiophene derivatives, see: Sabnis et al. (1999). For a related structure, see: Mukhtar et al. (2010). For further synthetic details, see: Gewald et al.  Table 1 Hydrogen-bond geometry (Å , ).
Data collection: SMART (Bruker, 1998); cell refinement: SAINT-Plus (Bruker, 1998); data reduction: SAINT-Plus; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012) and CAMERON (Watkin et al., 1996); software used to prepare material for publication: WinGX (Farrugia, 2012). Thiophene belongs to a class of heterocyclic compounds containing a five membered ring made up of one sulfur as heteroatom, that are widely used as building blocks in many agrochemicals and pharmaceuticals. 2-Aminothiophenes attract special attention because of their applications in pharmaceuticals, agriculture, pesticides and dyes (Sabnis et al., 1999). The most convergent and well established classical approach for the preparation of 2-aminothiophenes is Gewald's method (Gewald et al., 1966), which involves the multicomponent condensation of a ketone with an activated nitrile and elemental sulfur in the presence of diethylamine as a catalyst. Herein, we report the structure of the title compound, (I).

S2. Experimental
Step-1: 3.3 g of cyano ethyl acetate was weighed and transferred to RB flask and 5 g of acetyl acetone and 10 to 15 ml of ethanol were added to it. The whole mixture was stirred for 10 min. After stirring 1.6 g of elemental sulfur was added to the mixture and cold condition was maintained by using crushed ice. Later 5 ml of diethyl amine was added drop by drop the solution changes its color to red. After the completion of addition the solution was again kept for stirring (10 min). Ice pack was removed and stirring was continued for about an hour. The precipitated product (1) was filtered, dried and recrystallized from ethanol (yield: 68%, m.p. 430 K) Step-2: A mixture of compound 1 (10 mmol) and DMF-DMA (5 ml) was stirred at room temperature for 30 minutes.
To this was added ethanol and kept in room temperature to give a solid product (title compound) that was collected by filtration. The compound was recrystallized by slow evaporation from ethanol, yielding single crystals suitable for X-ray diffraction studies.

S3. Refinement
The H atoms were placed at calculated positions in the riding-model approximation with C-H = 0.96° A, 0.97 ° A and 0.93 ° A for methyl, methylene and methyne H-atoms respectively, with U iso (H) = 1.5U eq (C) for methyl H atoms and U iso (H) = 1.2Ueq(C) for other hydrogen atoms.

Figure 1
The molecular structure of the title compound with displacement ellipsoids drawn at the 50% probability level. H atoms are presented as small spheres of arbitrary radius.  Unit cell packing depicting C-H···π interactions with dotted lines. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.52 e Å −3 Δρ min = −0.33 e Å −3 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 cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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 > 2σ(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.