(4R*,5R*)-Diethyl 2-(4-nitrophenyl)-1,3-dioxolane-4,5-dicarboxylate

In the title compound, C15H17NO8, the nitro group is essentially coplanar with the aromatic ring [dihedral angle = 6.4 (3) Å]. The five-membered ring has a twist conformation. In the crystal, C—H⋯O interactions link the molecules into a helical chain propagating along [010].

In the title compound, C 15 H 17 NO 8 , the nitro group is essentially coplanar with the aromatic ring [dihedral angle = 6.4 (3) Å ]. The five-membered ring has a twist conformation. In the crystal, C-HÁ Á ÁO interactions link the molecules into a helical chain propagating along [010].

Comment
Antitumor platinum drugs are one of the most effective anticancer agents currently available. (2S,3S)-Diethyl 2,3-Oalkyltartrate analogues are starting materials for the synthesis of platinum complexes with antitumor activity (Kim et al., 1994), and they are also important intermediates in organic synthesis (Pandey et al., 1997). As part of our studies of the synthesis and characterization of such compounds, we herein report on the crystal structure of the title compound.
In the crystal, a C-H···O interaction (Table 1) links the molecules to form a a helical chain propagating along the b axis direction (Fig. 2).
Experimental 4-Nitrobenzaldehyde (299 mg, 1.98 mmol), (2S,3S)-diethyltartrate (378 mg, 1.84 mmol) and cyclohexane (10 ml) were placed in a round-bottomed flask, and 30 mg of 4-methylbenzenesulfonic acid was added. The flask was fitted with a water distributor. The mixture was heated under reflux for 4 h. The reaction mixture was then added dropwise to water (600 ml) with vigorous stirring. A pale yellow precipitate was obtained, filtered off and dried in vacuo. Colourless blocklike crystals, suitable for X-ray analysis, were obtained by slow evaporation of a methanol solution after 4 weeks.

Refinement
The NH and C-bound H-atoms were included in calculated positions and treated as riding atoms: N-H = 0.86 Å, C-H = 0.93, 0.96, 0.97 and 0.98 Å for CH(aromatic), CH 3 , CH 2 and CH(methine) H-atoms, respectively, with U iso (H) = k × U eq (N,C), where k = 1.5 for CH 3 H-atoms and k = 1.2 for all other H-atoms. In the final cycles of refinement, in the absence of significant anomalous scattering effects, 1257 Friedel pairs were merged and Δf " set to zero.    where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.21 e Å −3 Δρ min = −0.16 e Å −3 Extinction correction: SHELXL97 (Sheldrick, 2008), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.036 (9) 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 > 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.