E-[4-(β-d-Allopyranosyloxy)phenyl]-1-(4-chlorophenyl)prop-2-enone ethanol solvate

The title compound, C21H21ClO7·C2H5OH was synthesized by the condensation reaction between helicid [systematic name: 4-(β-d-allopyranosyloxy)benzaldehyde] and 4-chloroacetophenone in ethanol. In the molecular structure, the pyranoside ring adopts a chair conformation. In the crystal structure, the molecules are linked by intermolecular O—H⋯O hydrogen bonds involving the OH groups from the pyranoside unit and from the ethanol solvent molecule.

The title compound, C 21 H 21 ClO 7 ÁC 2 H 5 OH was synthesized by the condensation reaction between helicid [systematic name: 4-(-d-allopyranosyloxy)benzaldehyde] and 4-chloroacetophenone in ethanol. In the molecular structure, the pyranoside ring adopts a chair conformation. In the crystal structure, the molecules are linked by intermolecular O-HÁ Á ÁO hydrogen bonds involving the OH groups from the pyranoside unit and from the ethanol solvent molecule.
In the molecule of the title compound ( Fig. 1), the average of C-C bond lengths in the six-membered pyranoside ring is 1.522 (5) Å. The average C(sp 3 )-O and C(sp 2 )-O bond lengths are 1.414 (5) and 1.392 (4) Å, respectively. The pyranoside ring adopts a chair conformation with hydroxyl group at C3 in axial position and the other substituents at C1, C2 and C4, in equatorial positions.
In the crystal packing, the molecules are connected by intermolecular O-H···.O hydrogen bonds (Table 1) involving O1 and O7 atoms and the hydroxyl groups in the main molecule and in the ethanol solvent molecule, forming a threedimensional network.

S2. Experimental
To a solution of helicid (1.420 g, 5 mmol) in ethanol (20 ml), 10% aqueous solution of sodium hydroxide was added until helicid was dissolved completely. Then 4-chloroacetophenone (0.847 g, 5.5 mmol) was added dropwise, with the vessel placed in an ice bath. The reaction was monitored by TLC. After the reaction completed, the mixture was cooled to room temperature, and then neutralized with diluted hydrochloric acid. The solution was extracted three times with ethyl acetate, and the combined organic layers were dried with anhydrous Na 2 SO 4 , filtered, and evaporated in vacuo to get the crude product. The title compound was recrystallized twice from ethanol, and colourless single crystals were finally obtained by slow evaporation of an ethanol solution, at room temperature.

S3. Refinement
H atoms were positioned geometrically (C-H = 0.93-0.98 Å, O-H = 0.82 Å) and refined using a riding model, with U iso (H) = 1.2U eq (methylene C, aromatic C) or U iso (H) = 1.5U eq (O). The absolute configuration was determined by refinement of a Flack parameter, based on 562 measured Friedel pairs (Flack, 1983), and is in agreement with the expected configuration from the synthetic route.  The molecular structure of (I), with displacement ellipsoids drawn at the 30% probability level.