Di-tert-butyl (2R,3R)-2-{[(2E)-3-(4-acetyloxy-3-methoxyphenyl)prop-2-enoyl]oxy}-3-hydroxybutanedioate

In the title molecule, C24H32O10, one tert-butyl ester group is folded towards the central benzene ring while the other is directed away. The acetyl group is almost perpendicular to the benzene ring to which it is connected [C—C—O—C torsion angle = 90.4 (12)°]. The conformation about the ethene bond [1.313 (7) Å] is E. The atoms of the benzene ring and its attached ester group and part of the hydroxy tert-butyl ester side chain are disordered over two sets of sites in a 50:50 ratio. Linear supramolecular chains along the a axis mediated by hydroxy–carbonyl O—H⋯O hydrogen bonds feature in the crystal packing. The same H atom also partakes in an intramolecular O—H⋯O interaction.

In the title molecule, C 24 H 32 O 10 , one tert-butyl ester group is folded towards the central benzene ring while the other is directed away. The acetyl group is almost perpendicular to the benzene ring to which it is connected [C-C-O-C torsion angle = 90. 4 (12) ]. The conformation about the ethene bond [1.313 (7) Å ] is E. The atoms of the benzene ring and its attached ester group and part of the hydroxy tert-butyl ester side chain are disordered over two sets of sites in a 50:50 ratio. Linear supramolecular chains along the a axis mediated by hydroxy-carbonyl O-HÁ Á ÁO hydrogen bonds feature in the crystal packing. The same H atom also partakes in an intramolecular O-HÁ Á ÁO interaction.   coupling were isolated and recrystallized from 30% ethyl acetate/hexane to afford a crystalline solid from which the structure was determined by X-ray crystallography to confirm the retention of the (R,R)-stereochemistry, Fig. 1.

Related literature
The hydroxyl-H atom is bifurcated, forming an intramolecular O-H···O hydrogen bond with the adjacent carbonyl-O, Table, and an intermolecular O-H···O hydrogen bond with a translationally related carbonyl-O atom to form a linear supramolecular chain along the a axis, Fig. 1 and Table 1.
Experimental 1-O-Acetyl ferulic acid was prepared using a method analogous to that previously described by Zhao and Burke (1998), and the characterization data matched that previously described (Hosoda et al., 2001). 1-O-Acetyl ferulic acid (0.16 g, 0.67 mmol) was heated under reflux in dry benzene (10 ml) containing thionyl chloride (1 ml, 13.77 mmol). After 5 h the mixture was allowed to cool to room temperature and then concentrated in vacuo. The crude residue was taken up in dry benzene (3 ml) and added drop-wise to a solution of di-tert-butyl L-tartrate (0.21 g, 0.79 mmol) in dry pyridine (3 ml), then stirred at ambient temperature overnight. The mixture was concentrated and pyridine azeotropically removed with toluene. Purification with column chromatography (20% EtOAc/X4) and recrystallization from 30% EtOAc/X4 gave 1.2 to 1.5U eq (C,O)] and were included in the refinement in the riding model approximation. The molecule is disordered in some parts of the molecule. The disorder was treated as a 1:1 type of disorder. The aromatic rings were refined as rigid hexagons of 1.39 Å sides. For the disordered atoms, pairs of 1,2-related bond distances were restrained to within 0.01 Å of each other; these included atom-atom ordered as well as atom-atom disordered distances. The displacement parameters of the primed atoms were set to those of the unprimed ones, and the anisotropic displacement factors of the disordered atom atoms were restrained to be nearly isotropic. The two t-butyl groups are both ordered. However, the vibration of one of the four-carbon groups had to be tightly restrained to be nearly isotropic.

Figure 1
The molecular structure of the title compound showing the atom-labelling scheme and displacement ellipsoids at the 50% probability level. Only one component of the disordered atoms is shown for clarity.

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 > 2σ(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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ.