(2R,3R)-1,4-Dioxaspiro[4.4]nonane-2,3-dicarboxylic and (2R,3R)-1,4-dioxaspiro[4.5]decane-2,3-dicarboxylic acids

The title compounds, (CH2)nC3H2O(COOH)2 (n = 4, 5), display intermolecular hydrogen bonding, forming a two-dimensional framework.


Chemical context
Transition-metal catalysis has developed as a powerful tool to create a variety of carbon-carbon and carbon-heteroatom bonds. Enantioselective versions of these reactions are especially interesting in the light of the possible pharmaceutical applications. The general route to such processes supposes the use of transition metal complexes with chiral ligands (Yang et al., 2017). Therefore, easily accessible ligands of this type are of great importance for homogenous catalysis. Chiral phosphine ligands and amino acids are the most popular in this respect (Crassous, 2009). Examples of chiral carboxylate ligands are also known (Saget et al., 2012), which can be useful in the synthesis of chiral coordination compounds and materials derived from them (Lam et al., 2011). Various tartaric acid derivatives, which are also used in organic synthesis as chiral auxiliary agents to create chiral building blocks (Kassai et al., 2000;Seebach et al., 2001), might be particularly useful in solving the stated problem. Herein we report the synthesis and structures of two tartaric acid derivatives that may potentially be used as synthetic precursors of chiral transition-metal catalysts.

Figure 3
The structure of (2R,3R)-1,4-dioxaspiro[4.5]decane-2,3-dicarboxylic acid, (II). Displacement ellipsoids are drawn at the 50% probability level. Table 1 Selected bond lengths (Å ) for (I).  Figure 1 The synthesis of the title compounds (I) and (II).  (2) two interactions involving the O1-H1 and O3 atoms of each molecule. These chains are interconnected into a two-dimensional hydrogen-bonded double-layered framework parallel to (001) by the O4-H4 and O2 atoms. The complicated structure of the two-dimensional double-layered framework is shown in Fig. 5a, but it can best be visualized in the simplified scheme in Fig. 5b. It might be noted that some weak C-HÁ Á ÁO intermolecular interactions are also present (see the supporting information).

Figure 5
(a) The packing of (I) parallel to (001). Two interacting molecular layers are shown. Only the H atoms involved in hydrogen bonding (blue dashed lines) have been included. Displacement ellipsoids are drawn at the 50% probability level. (b) The simplified structure of the two-dimensional double-layered framework. Molecules (circles) and hydrogen bonds (solid lines) within the same layers are shown in the same colour (blue or red). Hydrogen bonds between two layers are shown as solid black lines. (Ianelli et al., 1992). The crystal structures of 14 related amide derivatives R 0 R 00 C 3 H 2 O 2 (CONR 2 ) 2 are also known (see the CSD and also Eissmann et al., 2012 and references therein). However, established crystal structures of related acids, R 0 R 00 C 3 H 2 O 2 (COOH) 2 , are limited to only one structure with R 0 = -C 6 H 4 -4-COOH and R 00 = H (LEPHIZ; Eissmann et al., 2012). This fact can be explained by some subtle problems with the individual isolation of pure acid samples because of the facile hydrolysis of the 1,3-dioxolane fragment during their preparation. Therefore, the synthesis and especially the crystallization of R 0 R 00 C 3 H 2 O 2 (COOH) 2 acids is a challenging task.  , 1977] was used as purchased. 1 H and 13 C{ 1 H} NMR spectra were recorded with Bruker AM-300 and Bruker DRX-500 spectrometers in CDCl 3 (Cambridge Isotope Laboratories, Inc., 99.8% 2 H) and in acetone-d 6 (Sigma-Aldrich, 99.9 atom % 2 H).

Synthesis and crystallization of
The synthesis of (I) was carried out analogously to that of (II), starting from 2.723 g (10 mmol) of (2R,3R)-diethyl 1,4dioxaspiro

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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.