(Z)-Methyl 4-({3-[(2,5-dioxoimidazolidin-4-ylidene)methyl]-1H-indol-1-yl}methyl)benzoate

In the title compound, C21H17N3O4, pairs of molecules form a planar[maximum deviation 0.0566 (9) Å] centrosymmetric imidazole dimer via two N—H⋯O hydrogen bonds. These dimeric units are linked by further N—H⋯O hydrogen bonds between the ester carbonyl group and the imidazolidine ring, formiing chains parallel to the c-axis direction. In addition, there are π–π stacking interactions between the planar imidazole pairs, with an interplanar spacing of 3.301 (2) Å. There is a double bond with Z geometry connecting the imidazolidine and indole units.

In the title compound, C 21 H 17 N 3 O 4 , pairs of molecules form a planar[maximum deviation 0.0566 (9) Å ] centrosymmetric imidazole dimer via two N-HÁ Á ÁO hydrogen bonds. These dimeric units are linked by further N-HÁ Á ÁO hydrogen bonds between the ester carbonyl group and the imidazolidine ring, formiing chains parallel to the c-axis direction. In addition, there arestacking interactions between the planar imidazole pairs, with an interplanar spacing of 3.301 (2) Å . There is a double bond with Z geometry connecting the imidazolidine and indole units.

S1. Comment
In continuation of our work on the radiosensitization activity of (Z)-2-(N-benzylindol-3-ylmethylene)quinuclidin-3-one and (Z)-(±)-2-(N-benzylindol-3-ylmethylene) quinuclidin-3-ol derivatives (Sekhar et al., 2003;Sonar et al., 2007), we have undertaken the design, synthesis and structural analysis of a series of (N-benzylindol-3-ylmethylene)imidazolidine-2,4-dione analogs with different substituents on both indole moiety and on the benzene ring of the Nbenzyl group. The primary goal for X-ray analysis of the title compound is to confirm the double-bond geometry and to obtain detailed information on the structural conformation of the molecule. This information will be useful in structureactivity relationship (SAR) analysis. The title compound was prepared by the reaction of methyl 4-((3-formyl-1Hindol-1-yl)methyl)benzoate with imidazolidine-2,4-dione in the presence of ammonium acetate in acetic acid at 391 K.
The compound was crystallized from a mixture of methanol and ethylacetate. The molecular structure and the atomnumbering scheme are shown in Fig.1. The indole ring is planar with bond distances and angles comparable with those previously reported for other indole derivatives (Mason et al., 2003;Zarza, et al., 1988). The X-ray studies revealed that the title compound is the Z isomer. The C8-C9 bond is in a transoid geometry with respect to the C10-C14 bond. The olefinic bond (C9=C10) has a planar atomic arrangement, since the r.m.s. deviation from the mean plane passing through atoms C1, C8, C9, N11 is 0.0349 (6) Å. Deviations from ideal geometry are observed in the bond angles around atoms C9, C10 and N11 (130.48 (12)°) due to repulsion between the indole ring C1 hydrogen and imidazolidine ring N11 hydrogen. The imidazolidine ring, which makes a dihedral angle of 10.03 (7)° with the adjacent aromatic ring, presents very small distortions around atoms N11, C12, N13 and C14.

S3. Refinement
H atoms were found in difference Fourier maps and subsequently placed in idealized positions with constrained distances of 0.98 Å (RCH 3 ), 0.99 Å (R 2 CH 2 ), 0.95 Å (C Ar H), 0.88 Å (N-H), and with U iso (H) values set to either 1.2U eq or 1.5U eq (RCH 3 ) of the attached atom.

Figure 1
A view of the molecule with the atom numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.

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