(R)-Di-tert-butyl 1,1′-binaphthyl-2,2′-dicarboxylate

The crystal structure of the title compound, C30H30O4, comprises two crystallographically independent half-molecules which are completed by crystallographic twofold symmetry. The dihedral angles between the naphthalene ring planes are 85.83 (3) and 83.69 (3)° for the two molecules. The atoms of the tert-butyl group of one molecule are disordered over two sets of sites with occupancies of 0.60:0.40. The crystal packing is achieved via π–π stacking interactions between the naphthyl groups of adjacent molecules, with a separation of 3.790 (1) Å between the centroids of the rings.

The crystal structure of the title compound, C 30 H 30 O 4 , comprises two crystallographically independent half-molecules which are completed by crystallographic twofold symmetry. The dihedral angles between the naphthalene ring planes are 85.83 (3) and 83.69 (3) for the two molecules. The atoms of the tert-butyl group of one molecule are disordered over two sets of sites with occupancies of 0.60:0.40. The crystal packing is achieved viastacking interactions between the naphthyl groups of adjacent molecules, with a separation of 3.790 (1) Å between the centroids of the rings.

Comment
For the (S)-form of 2,2'-dihydroxy-1,1'-binaphthyl (BINOL) was reported that during the reaction with equimolar amounts of pivaloyl chloride the formation of the corresponding 2,2'-pivalate is almost completely suppressed due to the steric hindrance rising from the bulky pivaloyl group (Hocke & Uozumi, 2002, 2003. However, we obtained the (R)-form of the 2,2'-dipivalate under forced conditions (see below) and determined its structure by X-ray crystallography.
An ORTEP diagram of the title compound is given in Fig. 1. The structure consists of two crystallographic independent molecules, which are located both on crystallographic twofold axes. The molecules belong to the point group C 2 and exhibit axial chirality. Molecular geometry parameters are within expected ranges. The tertiary butyl groups of one molecule show rotational disorder over two sites with occupancies of 0.60:0.40. The dihedral angles between the mean planes of the naphthyl groups are 85.83 (3) and 83.69 (3)° for the non-disordered and the disordered molecule, respectively. In comparison, an angle of 78.35 (5)° has been reported for the parent (R)-BINOL (Mori et al., 1993). The molecules interact via π-π stacking of the naphthyl groups of adjacent molecules with a separation of 3.790 (1) Å between the centroids of the rings C5-C10 and C15-C20. The mean interplanar distance is 3.59 Å and the offset is about 18.9°.

Experimental
To a solution of (R)-BINOL (4.34 mmol, 1.26 g) and triethylamine (26.7 mmol, 3.7 ml) in acetonitrile (13 ml) was added pivaloyl chloride (8.94 mmol, 1.1 ml) dropwise at 0°C. Subsequent, the reaction mixture was stirred over night and allowed to warm up to room temperature. Diethyl ether was added and the mixture was washed with aqueous 1 N HCl, saturated aqueous NaHCO 3 and brine three times, respectively. The organic phase was dried over MgSO 4 and the solvent was removed under reduced pressure. The crude product was purified by column chromatography over silica gel using ethyl acetate-n-hexane (1:6) as eluent. Yield: 1.15 g (58%). Single crystals of the title compound suitable for X-ray diffraction were grown from ethyl acetate-n-hexane (1:6) by slow evaporation of the solvent.

Refinement
The crystal structure was refined by full-matrix least-squares refinement on F 2 . Due to the absence of significant anomalous scattering effects, Friedel pairs have been merged. Anisotropic displacement parameters were introduced for all non-hydrogen atoms. Similar distance restraints were applied to the 1,2-and 1,3-distances of the disordered tertiary butyl group, respectively. The opposite C atoms of the disordered group were refined with equivalent anisotropic displacement parameters, supplementary materials sup-2 respectively. H atoms were placed at geometrically calculated positions and refined with U iso 1.2 times (1.5 for methyl groups) of their parent atoms and allowing to ride on them. The initial torsion angles of the methyl groups of the non-disordered tertiary butyl group were determined via a difference Fourier analysis. For the disordered tertiary butyl group those were calculated to be staggered. Fig. 1. ORTEP diagram of the title compound. Displacement ellipsoids are drawn at the 50% probability level. H atoms are omitted for clarity. Symmetry codes: (i) -x + 2, y, -z + 1/2, (ii)

Figures
x, -y + 1, -z + 1.  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.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )