N,1-Bis(4-chloro-2-methylbenzyl)-3-methyl-2-oxo-1,2,3,4-tetrahydroquinoline-3-carboxamide

In the title molecule, C27H26Cl2N2O2, the chloro-substituted benzene rings make dihedral angles of 83.29 (9) and 80.81 (9)° with the benzene ring of the tetrahydroquinoline group. The dihedral angle formed by the two chloro-substituted benzene rings is 40.87 (12)°. The six-membered N-containing ring is in a half-chair conformation. In the crystal structure, intermolecular N—H⋯O hydrogen bonds link molecules into centrosymmetric dimers.

In the title molecule, C 27 H 26 Cl 2 N 2 O 2 , the chloro-substituted benzene rings make dihedral angles of 83.29 (9) and 80.81 (9) with the benzene ring of the tetrahydroquinoline group. The dihedral angle formed by the two chloro-substituted benzene rings is 40.87 (12) . The six-membered N-containing ring is in a half-chair conformation. In the crystal structure, intermolecular N-HÁ Á ÁO hydrogen bonds link molecules into centrosymmetric dimers.  Table 1 Hydrogen-bond geometry (Å , ). N, 2,3, L. Porosa, R. D. Viirre and A. J. Lough

Comment
The title compound was prepared by an intramolecular Buchwald-Hartwig reaction of the corresponding malonamide under conditions we have previously described (Porosa & Viirre, 2009) (Fig. 3). The intention in this reaction was to preferentially arylate one of the two enantiotopic nitrogen atoms in the malonamide by exploiting the chiral influence of (R)-MOP ((R)-(+)-2-(diphenylphosphino)-2'-methoxy-1,1'-binaphthyl) as a catalyst component. Indeed, chiral HPLC analysis of the product indicated the highest enantioselectivity we have yet observed in this reaction, at 96% ee. It was hoped that the configuration of the major enantiomer could be determined from a crystal structure in order to correlate product and catalyst configuration and aid in the development of a mechanistic model for the reaction. The initially isolated product with 96% ee was a very viscous yellow oil. This was dissolved in diethyl ether and left to stand undisturbed at room temperature for several days. Upon evaporation of most of the solvent, a yellow oil was again obtained, but dispersed within it were small clear crystals. One of the single crystals was subjected to X-ray diffraction analysis and the crystal structure is reported herein.
The molecular structure of the title compound is shown in Fig. 1. To our surprise, it crystallized in a centrosymmetric space group. As there is no apparent mechanism by which the quaternary chiral center can epimerize, this demonstrates an impressive propensity for the racemate (essentially a 4% impurity in the initial product) to crystallize in preference to enantiopure material. In the title molecule, the C13-C18 and C21-C26 benzene rings form dihedral angles of 83.29 (9) and 80.81 (9)°, respectively with the C4-C9 benzene ring. The dihedral angle formed by the C13-C18 and C21-C26 benzene rings is 40.87 (12) °. The C1-C4/C9/N1 ring is in a half-chair conformation. In the crystal structure, intermolecular N-H···O hydrogen bonds link molecules into centrosymmetric dimers (Fig. 2).
Work is currently underway to crystallize enantiopure material.

N,N'-bis(4-chloro-2-methylbenzyl)-2-methylpropanediamide as a starting material. This material was recrystallized from
diethylether to obtain small amounts of diffraction quality crystals of the title compound.

Refinement
H atoms were placed in calculated positions with C-H distances in the range 0.95-0.99 Å; N-H = 0.88Å and included in the refinement in the riding-model approximation with U iso (H) = 1.2U eq (C,N) or U iso (H) = 1.5U eq (C) for methyl H atoms. 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.