Diethyl 1-(4-methylphenyl)-3-phenyl-5-oxopyrrolidine-2,2-dicarboxylate

In the title compound, C23H25NO5, the lactam ring adopts an envelope conformation and both ethoxycarbonyl side chains show an s-cis conformation: one is nearly planar, the dihedral angle between CO2 and OCH2CH3 groups being 7.95 (14)° and the other is almost orthogonal, the C—O—C—C torsion angle being 85.33 (9)°. Dimers related by inversion symmetry are stabilized by C—H⋯O hydrogen bonds. The crystal structure is consolidated by weak intermolecular C—H⋯O interactions. Weak intramolecular interactions of the same kind also occur.

JKR thanks the Ministerio de Educació n y Ciencia for funding a short sabbatical visit (SAB2006-0199) to the Universidade da Coruñ a. The authors wish to thank Dr Ana Isabel Balana Gracia (SAI-UDC technician) for her helpful comments and are indebted to the CESGA (Xunta de Galicia -Spain) for the use of the Cambridge Structural Database. Funds were provided by the Xunta de Galicia through the project PGIDIT05TAM10301PR.
The ethoxycarbonyl side chain involving O2-C18-O3-C19-C20 adopts a s-cis conformation, with atoms of the group being nearly co-planar, the dihedral angle between CO 2 and OCH 2 CH 3 moieties being 7.95 (14)°; the other ethoxycarbonyl chain (O4-C21-O5-C22-C23) is also s-cis, the ethyl and the carboxylate moieties in a gauche relationship, the torsion angle of C21-O5-C22-C23 being 85.33 (9)°. The geometry of the title compound is similar to that of pirrolidinones (Nigam et al. 1989), (Ray et al., 2004), (Ray et al., 2010), (Kandasamy et al., 1995). The crystal structure contains van der Waals and C-H···O weak interactions, the latter are listed in Table 1. Carbonyl O atoms O1, O2 and O4 interact with two H atoms; such intermolecular interactions could be classified as supportive (Desiraju, 2005). Inversion dimers are formed involving oxygen atoms O2 and O4; in the first case, the same pair of molecules are linked, each oxygen O2 of one molecule interacting with H atoms H2a and H13 of the other (symmetry code: -x, 1 -y, 2 -z). When oxygen O4 is considered, three molecules participate; there is an inversion dimer due to the intermolecular interactions between oxygen O4 and hydrogen H2b (symmetry code: -x, 1 -y, 1 -z), and the same applies for O4 and H22b (symmetry code: 1 -x, 1 -y, 1 -z). In addition to those dimers, the interaction of oxygen O1 with H atoms H15 (symmetry code: x, 1 + y, z) and H22a (symmetry code: -1 + x, y, z) results in sheets propagating in the ab plane. The angle between the two C-H..O hydrogen bonds bifurcated at O1 (C15-H15-O1 and C22-H22a-O1) is almost a right angle (86.7°).

Experimental
The title compound was synthesized via an intermolecular Michael addition reaction, followed by an intramolecular amidification reaction, between diethyl 4-methylanilinomalonate (synthesized by the condensation reaction between 4-methylaniline and diethyl bromomalonate) in the presence of triethylamine, using dry benzene as solvent. Single crystals were grown by slow evaporation at room temperature of a solution of the resulting compound in 2-propanol. Yield 79%.

Refinement
Hydrogen atoms were found in subsequent difference Fourier maps and included in observed positions and refined as free isotropic atoms.
ALERTs all level C PLAT029_ALERT_3_C _diffrn_measured_fraction_theta_full Low. 0.98 RESPONSE: REason unknown. Optimized strategy by the software in order to get high completeness to resolution=0.75 A and enough redundancy and cut off in the refinement at 2theta=51, optimizing the the ratio parameters/data. Diethyl 1-(4-methylphenyl)-3-phenyl-5-oxopyrrolidine-2,2-dicarboxylate

Special details
Experimental. Data was collected using a X8 APEX II BRUKER-Nonius diffractometer equipped with an KRYOFLEX low-temperature apparatus operating at 100 K. A suitable crystal was chosen and mounted on a glass fiber using grease. Data were measured using omega scans of 0.5° per frame for 10 s, such that a total of 2870 frames were collected in a optimized strategy and with a final resolution of 0.75 Å. Data integration and reduction was performed using the APEX2 (Bruker, 2009) software suite. Absorption corrections were applied using SADABS (Bruker, 2009). The structures are solved by direct methods using the SHELX97 program and refined by least squares on F 2 SHELXL97, incorporated in the Apex2 software suite. 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.
All non-hydrogen atoms were refined anisotropically. Hydrogen were found in subsequent difference Fourier maps and included as isotropic atoms.