Ethyl 3,4-dimethyl-1H-pyrrole-2-carboxylate

The non-H atoms of the title compound, C9H13NO2, are almost coplanar (r.m.s. deviation = 0.0358 Å). Weak intermolecular N—H⋯O hydrogen bonds link the molecules into zigzag chains along the b axis with graph-set motif C(5). The chains are further linked into a three-dimensional network by C—H⋯O hydrogen bonds and C—H⋯π interactions.

The non-H atoms of the title compound, C 9 H 13 NO 2 , are almost coplanar (r.m.s. deviation = 0.0358 Å ). Weak intermolecular N-HÁ Á ÁO hydrogen bonds link the molecules into zigzag chains along the b axis with graph-set motif C(5). The chains are further linked into a three-dimensional network by C-HÁ Á ÁO hydrogen bonds and C-HÁ Á Á interactions.

Comment
Schiff bases containing pyrrole units have been extensively investigated due to their excellent coordination abilities (Wu et al., 2003). As a part of our studies on bis(pyrrol-2-yl-methyleneamine) ligands (Wang et al., 2008), the crystal structure of the title compound is reported here.
The non-hydrogen atoms of the title molecule ( Fig. 1) are situated in a fair plane (r.m.s. deviation of the non-hydrogen atoms being 0.0358 Å). In the crystal structure, the molecules are linked by weak intermolecular N-H···O hydrogen bonds, forming zig-zag chains with the graph-set motifs C(5) (Etter & MacDonald, 1990). The chains are extended along the b axis (Tab. 1, Fig. 2, Fig. 3). The structure is also stabilized by the C-H···O hydrogen bonds (Tab. 1) and C-H···π-electron ring interactions (Tab. 1).

Experimental
The title compound was prepared according to Helms et al. (1992). Acetic acid (114 ml) was placed in a 1-L round-bottom flask and heated to 85 °C. Sodium acetate (31.09 g), 27.54 g of sodium 2-methyl-3-oxo-l-butene-1-oxide, 37.20 g of diethyl 2-(hydroxyimino)malonate, and a solution of 47 ml of acetic acid in 19.6 ml of H 2 O were then added in the respective order. The reaction temperature was raised to 95 °C, and 43.26 g of Zn-dust was added over 45 min while maintaining the temperature between 95 and 110 °C. After the addition of Zn-dust had been completed, the mixture was stirred while keeping its temperature at 110 °C for further 45 min. The reaction mixture was then poured into 500 ml of ice water. The obtained solid was filtered, washed with water and subsequently dissolved in dichloromethane. The solution was washed with saturated sodium hydrogencarbonate, dried with anhydrous sodium sulfate and then the solvent was removed under reduced pressure. The crude product was purified by column chromatography on a silica gel [R f = 0.68, petroleum ether-ethyl acetate (100:1) as an eluent] to yield 4.82 g (13%) of the title compound. Colourless block crystals [average size: 0.25× 0.25 × 0.20 mm] were obtained by slow evaporation of the ethyl acetate solution at room temperature.

Refinement
All the H atoms were located in the difference electron density map. The H atoms were situated into the idealized positions with the carrier atom-H distances = 0.93 Å for aryl, 0.97 for methylene, 0.96 Å for the methyl and 0.86 Å for the secondary amine hydrogens. The U iso values were constrained to be 1.5U eq of the carrier atom for the methyl H atoms and 1.2U eq for the remaining H atoms.
supplementary materials sup-2 Figures   Fig. 1. The title molecule with the displacement ellipsoids shown at the 50% probability level.   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.