Ethyl 2-hydroxy-5-oxo-4-phenyl-2,3,4,5-tetrahydropyrano[3,2-c]chromene-2-carboxylate

The main structural unit of the title compoud, C21H18O6, is a fused three-ring group consisting of coumarin and tetrahydropyrane ring systems. Two C atoms of the tetrahydropyran ring are displaced by 0.295 (3) and −0.360 (2) Å from the mean plane of coumarin ring. The dihedral angle between the phenyl and coumarin rings is 73.94 (3)°. Intermolecular O—H⋯O hydrogen bonds are present in the crystal structure.

The main structural unit of the title compoud, C 21 H 18 O 6 , is a fused three-ring group consisting of coumarin and tetrahydropyrane ring systems. Two C atoms of the tetrahydropyran ring are displaced by 0.295 (3) and À0.360 (2) Å from the mean plane of coumarin ring. The dihedral angle between the phenyl and coumarin rings is 73.94 (3) . Intermolecular O-HÁ Á ÁO hydrogen bonds are present in the crystal structure.
coumarin and (E)-ethyl 2-oxo-4-phenylbut-3-enoate, can act as an intermediate in organic and natural product synthesis. In this article, the crystal structure of the title compound, ethyl 2-hydroxy-5-oxo-4-phenyl-2,3,4,5-tetrahydropyrano[3,2c]chromene-2-carboxylate was described (Fig. 1). The main structural unit is a three-ring group consisting of a coumarin ring and a tetrahydropyrane. Two carbon atoms of the tetrahydropyrane structure are not coplanar with the coumarin backbone: one carbon atom lies 0.295 (3) Å from the mean plane of coumarin ring and the other lies 0.360 (2) Å from the plane in opposite direction. The dihedral angle between benzene and coumarin rings is 73.94 (3) °. The distance from O1 of the hydroxyl group to coumarin plane is 1.664 (2) Å. In addition, intermolecular O-H···O hydrogen bonds in the crystal are observed (Fig. 2).

Experimental
The title compound was synthesized by treating (E)-ethyl 2-oxo-4-phenylbut-3-enoate (2.04 g,10 mmol) with 4-hydroxycoumarin (1.62 g, 10 mmol) in the presence of triethylamine as a catalyst in dichloromethane (30 ml) under stirring at room temperature for 24 h. The solvent was distilled under vacuum, and the residue was purified by flash column chromatography (silica gel, Hex/AcOEt, v/v, 3:1) giving the title compound (3.3 g, 90%). The compound (E)-ethyl 2-oxo-4-phenylbut-3-enoate was obtained from commercially available benzaldehyde by condensation with pyruvic acid and subsequent esterification with ethanol. Suitable crystals of the title compound were obtained by slow evaporation of dichloromethane solution at room temperature.

Special details
Geometry. The tetrahydropyrane structure in the crystal displays an envelope configuration, with atom C2 at the flap position, displaced by 0.603 (2) Å from the mean plane of the other atoms.
Refinement. Refinement using reflections with F 2 > 2.0 σ(F 2 ). The weighted R-factor(wR), goodness of fit (S) and R-factor (gt) are based on F, with F set to zero for negative F. The threshold expression of F 2 > 2.0 σ(F 2 ) is used only for calculating R-factor (gt).