Facile Preparation of 1 , 2-Diols from Chalcones : An NMR Spectroscopy and X-Ray Crystallography Study

Structures of 2-(naphthalen-2-ylmethyl)-2,3-dihydro-1H-indene-1,2-diol (C20H18O2), compound 1 and 1-(3,4-dimethoxyphenyl)-3-methoxy-3-(4-nitrophenyl)propane-1,2-diol chloroform (C18H21NO7·CHCl3) compound 2 were established by spectral and X-ray diffraction studies. Compound 1 crystallizes in the orthorhombic space group P212121 with unit cell parameters a = 5.2177 (6), b = 13.903 (2), c = 21.121 (2) Å, Z = 4. Compound 2 crystallizes in the triclinic space group P-1 with unit cell parameters a = 9.238 (1), b = 9.879 (1), c = 12.636 (1) Å, α = 102.004 (1), β = 92.356 (1), γ = 90.779 (1) ̊, Z = 2. These two new molecules arise from a facile preparation of 1,2-diols from chalcones and have been fully characterized. Based on the crystallographic information obtained for compound 1, the relative configuration for the chiral centers is 1S and 2S. In structure 1, both hydroxyl groups adopt an anti-conformation with a torsion angle O1-C1-C2-O2 value of 93.1 (2) ̊ [in molecule 2, both hydroxyl groups adopt a trans-conformation with a torsion angle O1-C1-C2-O2 value of −171.0 (2) ̊]. In both structures, the molecules in the crystal are linked by intermolecular hydrogen bonds O-H···O and C-H···O interactions and adjacent molecules are interconnected by intermolecular weak C-H···π and C-H···Cl interactions which give additional support to molecular packing stability.


Introduction
In the field of organic chemistry, there is a need to optimize stereospecific reactions in order to get the desired products within a high yield.The synthesis of diols from carbonyl derivatives has been widely used mainly as a previous step for introducing carbon-carbon double bonds, since these methods allow the control of stereochemistry and the position of unsaturation [1].On the other hand, 1,2-diols are found frequently in natural products in carbohydrates, polyketides, and alkaloids, and for this reason modern synthetic methods of natural products involve enantioselective or catalytic asymmetric procedures [2].The use of metal hydrides on reduction of ketones to alcohols has been invaluable in the synthesis of diols which is commonly carried out in acidic medium [3].The use of borohydride gives a selective reduction from α, β-unsaturated ketones to allylic alcohols [4].
Here we report two new molecules that arise from a facile preparation of 1,2-diols from chalcones and have been fully characterized by NMR and X-ray crystallography techniques.

Physical Measurements
Melting points were determined in on Fisher-Jones melting point apparatus and are uncorrected.IR absorption spectra were recorded in the 4000 -400 cm −1 range as KBr pellets on a Perkin Elmer 283-B spectrophotometer. 1 H and 13 C NMR spectra were recorded in CDCl 3 and DMSO-d 6 on a Unity Varian 300 MHz or 500 MHz spectrometer using TMS as an internal reference.

Determination of the Crystal Structures
Both X-ray data were collected on a Bruker Smart APEX AXS CCD area detector with a graphite monochromator and Mo Kα radiation (λ = 0.71073 Å) at room temperature by the ω scan mode.All collected data were reduced using SAINT [8] and the empirical absorption corrections were performed using SADABS program [8].The details were shown in Table 1.

Refinement Details
All reflections were defined based on F 2 .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.

Geometric Details
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.

Structure Details
Both structures were solved by direct methods [9], and then refined by full-matrix least-squares technique; the position and anisotropic parameters of all the non-hydrogen atoms were obtained.
For compound 1, the Flack [10] absolute structure parameter = 0.3 (2) and its absolute configuration is inferred from the known stereochemistry of 3'-(naphthalen-2-yl)spiro[indene-2,2'-oxiran]-1(3H)-one compound deduced from chemical studies.All relevant tables and figures are based on this configuration.Table 2 showed some crystal and refinement parameters.Atomic coordinates and displacement parameters of both compounds were shown in Table 3 and Table 4, these data the structures were gained, which was shown in Figure 1.This figure was drawn with 50% displacement ellipsoids using ORTEP-3 for Windows [11].The geometry of the molecule was calculated using the WinGX [12] and PARST [13] [14] software's.
In structure 1, the distances between the Cg gravity centers of naphthalene and indene; between naphthalene symmetry related molecules; and between indene symmetry related rings are 5.20; 5.22 and 4.99 Å, respectively.The distance between the Cg gravity center of the ring C4-C9 and the H3B of a symmetry related molecule is 2.79 Å.
In structure 2, the distances between the Cg gravity centers of phenyl C4-C9 rings; phenyl rings C4-C9 and C12-C17; phenyl ring C4-C9 and H18B of the methoxy group at C3; and phenyl ring C12-C17 and H18C of the  (9) ring motifs [15].In molecule 1, each molecule is connected to two of its neighbors via intermolecular hydrogen bonds; the packing is viewed down the c-axis (Figure 2).The structure is further linked by C-H•••π stacking interactions.In structure 2 each molecule is connected to one of its neighbors via intermolecular hydrogen bonds, to form a two dimensional supramolecular structure along with the bc crystallographic plane (Figure 3).These hydrogen bond interactions generate two ( 14) and (10) ring motifs [14].The structure is linked by C-H•••π stacking and three C-H•••Cl interactions forming a 3D polymer, the C-H•••π distances and angles for Cg gravity centers to C4-C9 and C12-C17 phenyl rings are given in Figure 4.For geometrical details and notations of all of these hydrogen bonds and intermolecular interactions are given in Table 5.

Conclusion
The present study demonstrates the synthesis and chemical characterization by IR, 1 H-NMR and 13      successfully grown from solution by slow evaporation technique at room temperature using ethyl acetate as a solvent (compound 2, chloroform: hexane).IR and 1 H-NMR are used to confirm the functional groups.During the crystallization process of compound 1, the diasteromer (1S and 2S) was obtained while no chiral reagent was used in the reaction.

Figure 2 .
Figure 2. The packing diagram for 1 projected along the c-axis.

Table 1 .
Data collection and handling.

Table 2 .
Crystal and refinement parameters.
The letters A, B and C on H atoms are only used for identification purposes for instance the hydroxyl and methyl groups.