2,2-Diethyl 3,4-dimethyl 5-(4-cyanophenyl)pyrrolidine-2,2,3,4-tetracarboxylate

The title compound, C21H24N2O8, was synthesized by a 1,3-dipolar cycloaddition reaction of dimethyl fumarate, diethyl 2-aminomalonate and 4-cyanobenzaldehyde. Both methyl ester groups display a trans configuration and the pyrrolidine ring possesses an envelope conformation, with the C atom in the 3-position as the flap. In the crystal, N—H⋯N hydrogen bonds and weak C—H⋯O interactions occur.


Comment
Facile synthesis of structurally diverse heterocycles is important in chemical biology. Five-membered pyrrolidines compounds is an important class of heterocyclic compounds with wide spread applications to the synthesis of biologically active compounds and natural alkaloids (Coldham & Hufton, 2005;Pandey et al., 2006;Schreiber et al., 2000). Its crystal structure is reported here.
The molecular structure of (I) is shown in Fig. 1. Bond lengths and angles in (I) are normal. The pyrrolidine ring possesses an envelope conformation. The crystal packing is stabilized by C-H···O and N-H···N hydrogen bonds (Table   1).

Experimental
To a solution of 4-cyanobenzaldehyde (0.065 g, 0.5 mmol), sodium sulflate (0.1 g) and diethyl 2-aminomalonate (0.070 g, 0.4 mmol) in chloroform (4 ml) was added dimethyl fumarate (0.145 g, 1 mmol). The mixture was stirred at 323 K for 2 d and then cooled to room temperature, the solvent was evaporated under reduced pressure and the residues was purified by flash chromatograghy on silica gel. The colourless powder was obtained. Single crystals suitable for X-ray diffraction were obtained by slow evaporation of an ethyl acetate solution.

Refinement
H atoms on N atoms were located in a difference Fourier map and refined isotropically. The carbon-bound hydrogen atoms were placed in calculated positions, with C-H = 0.93-0.98 Å, and refined using a riding model, with U iso (H) =1.5U eq (C) for methyl H atoms and U iso (H) =1.2U eq (C) for the others. As no significant anomalous scatterings Friedel pairs were merged.  The molecular structure of (I) with 30% probability displacement ellipsoids (arbitrary spheres for H atoms).  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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq O2