Dimethyl 4-ethoxy-1-(4-methyl-2-pyridyl)-5-oxo-2,5-dihydro-1H-pyrrole-2,3-dicarboxylate

In the title compound, C16H18N2O6, the dihedral angle between the aromatic ring planes is 8.11 (6)°. One of the O atoms is disordered over two sites of equal occupancy. In the crystal structure, aromatic π–π stacking [centroid-to-centroid separation = 3.5503 (8) Å] helps to consolidate the packing.


Related literature
Here we report the synthesis and crystal structure of the title compound, (I). It is rational to assume that compound 1 (Fig. 1) is produced from the initial production of ylide intermediate produced from three-component reaction of DMAD, 4-methyl-2-aminopyridine and triphenylphosphine, which then reacted with ethyl chlorooxoacetate to produce an oxamate derivative that underwent intramolecular Wittig reaction to give the products. Crystal packing of I is shown in Fig. 2. A considerable feature of the compound (I) is the presence of π-π stacking interactions between six and five membered rings

Experimental
To a magnetically stirred solution of PPh 3 (0.26 g, 1 mmol) and 4-methyl-2-aminopyridine (0.9 g, 1 mmol) in CH 2 Cl 2 (10 ml) was added drop-wise a mixture of dimethyl acetylenedicarboxylate DMAD (0.14 g, 1 mmol) in CH 2 Cl 2 (3 ml) at room temperature over 2 min. The reaction mixture was then stirred for one more minute, then triethylamine (1 mmol) and ethyl chlorooxoacetate (1 mmol) was added and the reaction mixture was stirred for more 24 h. Solvent was evaporated and the residue was purified by column chromatography on SiO 2 using EtOAC-hexane (1:4) mixture as eluent. The solid formed was filtrated, recrystallised from dichloromethane/ethanol (2:1) to yield colourless prisms of (I).

Refinement
The H(C) atoms were placed in calculated positions and refined as riding with U iso (H) = 1.2U eq (C). Fig. 1. The molecular structure of (I). Atoms are represented by 50% displacement ellipsoids. The occupancies of positions of disordered O6 atom are equal (0.5).

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (