Menthyl 2-oxo-2H-chromene-3-carboxylate

The title compound, C20H24O4, was synthesized from the reaction of 2-oxo-2H-chromene-3-acyl chloride and menthol. The mean plane of the ester group and that of the four essentially planar (maximum deviation 0.0112 Å) C atoms of the chair-form cyclohexyl ring form dihedral angles of 43.8 (3) ° and 81.8 (1)°, respectively, with the mean plane of the coumarin ring system. In the crystal structure, weak intermolecular C—H⋯O hydrogen bonds connect the molecules into a two-dimensional network.

The title compound, C 20 H 24 O 4 , was synthesized from the reaction of 2-oxo-2H-chromene-3-acyl chloride and menthol. The mean plane of the ester group and that of the four essentially planar (maximum deviation 0.0112 Å ) C atoms of the chair-form cyclohexyl ring form dihedral angles of 43.8 (3) and 81.8 (1) , respectively, with the mean plane of the coumarin ring system. In the crystal structure, weak intermolecular C-HÁ Á ÁO hydrogen bonds connect the molecules into a two-dimensional network.
This work was supported by the Natural Science Foundation of Henan Province (No. 2009 A150012).
The molecular structure of (I) is shown in Fig. 1. The compound is composed of a coumarin core with a menthyloxycarbonyl in 3-position. The dihedral angle between the plane of ester group and the plane of coumarin ring system is 43.8 (3)°.
The dihedral angle between the coumarin ring system and the plane defined by four essentially planar carbon atoms (C11/ C13/C14/C16) of the chair form cyclohexyl ring is 81.8 (1)°. In the crystal structure, weak intermolecular C-H···O hydrogen bonds connect molecules into a two-dimensional network (Fig. 2).

Experimental
A solution of menthol (0.0072 mol) dissolved in dried methyl dichloride (DCM) (25ml) was added dropwise to a solution of 2-oxo-2H-chromene -3-acyl chloride (0.0072 mol) dissolved in DCM (25 ml) and triethylamine (1 ml) at room temperature. The reaction mixture was stirred for 24 h (mornitored by TLC). The mixture was then neutralized with 5% HCl and washed with saturated NaHCO 3 and brine respectively. The organic phase was dried over Na 2 SO 4 and evaporated under the reduced pressure. The resulting residue was purified by column chromatography (EtOAc: petroleum ether) to give the pure compound. Single crystals of the title compound suitable for X-ray diffractions were obtained by slow evaporation of a mixed solvent (ethyl acetate: petroleum ether = 1:1, 10 ml) solution of the title compound (0.035 g).

Refinement
In the absence of significant anomalous dispersion effects Friedel pairs were merged before refinement. The absolute configuration is based on that of the starting material. All H atoms were placed in caculated positions, with C-H = 0.93 Å, and U iso (H)=1.2U eq (C) for aromatic H atoms; C-H = 0.96 Å, and U iso (H)=1.5 U eq (C) for methy H atoms. The final difference map had a highest peak at 0.64 Å from atom O2 and a deepest hole at 1.60 Å from atom C3.