Dimethyl dl-2,3-dibenzyl-2,3-diisothiocyanatosuccinate

The title compound, C22H20N2O4S2, has approximate molecular twofold symmetry. In the crystal, the presence of C—H⋯π interactions leads to the formation of zigzag chains along [001].

The title compound, C 22 H 20 N 2 O 4 S 2 , has approximate molecular twofold symmetry. In the crystal, the presence of C-HÁ Á Á interactions leads to the formation of zigzag chains along [001].

Comment
The title compound was synthesized as a part of a larger project focusing on the synthesis of 2,3-disubstituted 2,3-diaminosuccinic acid derivatives obtained from titanium (IV) enolates of 2-isothiocyanato-carboxylates via C-C bond formation in oxidative homo-coupling of titanium (IV) enolates of 2-isothiocyanato-carboxylic esters (Cież, 2007;Cież et al., 2008). The main reason for the interest in vicinal diisothiocyanates is related to their wide application in organic syntheses (Morel & Marchand, 2001). The molecule, crystal structure of which is presented here, belongs to the rare class of organic compounds.
There are two chiral centres in the molecule, localized on atoms C2 and C3, both with the same absolute configuration (R,R enantiomer shown in Figure1).
The crystal structure of the title compound is stabilized by weak interactions. The strongest are C-H···π interactions (Arunan et al., 2011a;Arunan et al., 2011b;Malone et al., 1997). They are formed between molecules related via glide plane c. The distance between hydrogen atom and centroid of the aromatic ring (Cg) is 2.611Å, with angle C38-H···Cg = 145.17°. The additionally defined angle of approach of the vector HCg to the plane of the aromatic ring, θ = 77°, and horizontal distance 0.6Å, classify this C-H···π as the second common geometry for this type of interaction observed in crystal structures (type III according to Malone et al., 1997). Intermolecular C-H···π interactions between neighbouring molecules observed in this structure form a zigzag-like chain in the The second aromatic moiety of the DL-2,3-dibenzyl-2,3-diisothiocyanato-succinic acid dimethyl ester is not involved in C-H···π. It is placed in short distance to a corresponding ring of the neighbouring molecule, related via the inversion centre (C24···C24 ii = 3.390 (2)Å, where (ii) is -x + 2, -y, -z + 2). However, the overlapping of the aromatic rings is not observed. This suggests a hydrophobic association.
Colourless, block single crystals suitable for X-ray diffraction were obtained from ethanol solution by slow evaporation of solvent at ambient conditions.

Refinement
All non-hydrogen atoms were refined anisotropically using weighted full-matrix least-squares on F 2 . All hydrogen atoms were calculated at idealized positions and refined using a riding model with C-H = 0.95Å and U iso (H) = 1.2U eq (C) for aromatic hydrogen atoms, C-H = 0.99Å and U iso (H) = 1.2U eq (C) for methylene groups, C-H = 0.98Å and U iso (H) = 1.5U eq (C) for the methyl groups refined as rotating group.   Special details Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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 > 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.