meso-4,5-Diphenylimidazolidin-2-one

The crystal structure determination of the title compound, C15H14N2O, confirms the cis relationship between the phenyl groups at the 4- and 5-positions on the imidazolidine ring. The dihedral angle between the two phenyl rings is 48.14 (6)°. In the crystal structure, intermolecular N—H⋯O hydrogen bonds link molecules into centrosymmetric dimers. These dimers are, in turn, linked into a two-dimensional network via weak N—H⋯π(arene) interactions and π–π stacking interactions with centroid–centroid distances of 3.6937 (11) Å.

The crystal structure determination of the title compound, C 15 H 14 N 2 O, confirms the cis relationship between the phenyl groups at the 4-and 5-positions on the imidazolidine ring. The dihedral angle between the two phenyl rings is 48.14 (6) . In the crystal structure, intermolecular N-HÁ Á ÁO hydrogen bonds link molecules into centrosymmetric dimers. These dimers are, in turn, linked into a two-dimensional network via weak N-HÁ Á Á(arene) interactions andstacking interactions with centroid-centroid distances of 3.6937 (11) Å .

Comment
The title compound is a meso-compound, and is therefore achiral. The trans-isomer is chiral, and both antipodal isomers have been synthesized (Sankhavasi et al., 1991). The crystal structure of the (4R,5R)-isomer has already been determined (Siegler & Long, 2006). Enantiopure samples of the trans-isomers have found use as precursors for chiral auxiliaries (Sankhavasi et al., 1991), chiral catalysts (Isobe et al., 1998), and chiral ligands (Lou et al., 2004). The title compound might also be of similar use if desymmetrization can be accomplished by selective reaction of one of the two enantiotopic nitrogen atoms, for instance using an enantioselective Buchwald-Hartwig reaction (Porosa & Viirre (2009).
The title compound was prepared according to the reaction scheme shown in Fig. 3. The imine-amide precursor is readily prepared by heating benzaldehyde with NH 4 OAc according to a literature procedure (Proskurnina et al., 2002). This compound was subjected to exhaustive hydrolysis, by heating in a mixture of HBr and acetic acid for four days, and the resultant meso-diamine was then treated with carbonyl diimidazole, resulting in the title compound.
The molecular structure is shown in Fig. 1 and confirms the cis-relationship between the phenyl groups at the 4 and 5 positions (atoms C1 and C3 by the crystallographic labelling scheme). This relative stereochemistry is initially set in the formation of the imine-amide species, which involves an electrocyclization governed by orbital symmetry considerations.
Epimerization did not occur, even upon prolonged exposure to strong acid and heat in the hydrolysis of the imine and amide groups.

Experimental
A suspension of 1,2-diamino-N-benzoyl-N'-benzylidene-1,2-diphenylethane (23.0 g, 57 mmol) in a mixture of glacial acetic acid (115 ml) and 48% aqueous HBr (230 ml) was heated to reflux for four days. The mixture was then cooled in an ice bath and diethyl ether (200 ml) was added and vigourous stirring was continued for 30 minutes before being filtered and washed with diethyl ether. The solid filtrate was added to 100 ml of ice-cold 40% aqueous NaOH, which was then extracted three times with CH 2 Cl 2 (150 ml). The organic extracts were evaporated to dryness and recrystallized from water to obtain meso-1,2-diamino-1,2-diphenylethane (7.8 g, 65% yield mmol) was dissolved in CH 2 Cl 2 (50 ml) and cooled in an ice bath, while a solution of 1,1'-carbonyldiimidazole (8.108 g, 50 mmol) in CH 2 Cl 2 (250 ml) was added dropwise. The mixture was stirred for two hours, and the solvent was evaporated under reduced pressure. The solid was taken up in MeOH (200 ml), cooled in an ice bath, 20 ml of 40% aqueous NaOH was added, supplementary materials sup-2 and the mixture was stirred for 30 minutes. Methanol was evaporated under reduced pressure, and the remaining aqueous solution was cooled in an ice bath and acidified to pH = 1 with 0.5 M HCl, upon which the title compound crystallized. The crystals were filtered to obtain meso-4,5-diphenylimidazolin-2-one (5.560 g, 97% yield

Refinement
H atoms bound to C were placed in calculated positions with C-H distances in the range 0.95-1.00Å and included in the refinement in a riding-model approximation with U iso (H) = 1.2U eq (C). The H atoms bonded to N atoms were refined independently with isotropic displacement parameters. Fig. 1. The molecular structure showing 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 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.