4-Hydroxy-3-[(2E)-3-(3,4,5-trimethoxyphenyl)prop-2-enoyl]-2H-chromen-2-one

A new chalcone of the coumarin, C21H18O7, containing an annulated α-pyrone ring, was obtained by condensation of the borate complex of acyl(hydroxy)coumarin with trimethoxybenzaldehyde. The structure exhibits intramolecular hydrogen bonding between the hydroxyl oxygen and the ketonic oxygen in the coumarin group. The bicyclic coumarin fragment and the benzene ring form a dihedral angle of 17.1 (4)°. The crystal packing involves dimers interconnected by C—H⋯O hydrogen bonding.

A new chalcone of the coumarin, C 21 H 18 O 7 , containing an annulated -pyrone ring, was obtained by condensation of the borate complex of acyl(hydroxy)coumarin with trimethoxybenzaldehyde. The structure exhibits intramolecular hydrogen bonding between the hydroxyl oxygen and the ketonic oxygen in the coumarin group. The bicyclic coumarin fragment and the benzene ring form a dihedral angle of 17.1 (4) . The crystal packing involves dimers interconnected by C-HÁ Á ÁO hydrogen bonding.
Professor A. Driss is acknowledged for his contribution to the X-ray diffraction data collection at the Laboratoire de cristallochimie-Université Tunis ElManar.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: HG2517).

Comment
The non-linear optical materials (NLO) effect in the organic molecules originates from a strong electron-donor-acceptor intermolecular interaction, delocalized π-electron system (Marcy et al., 1995;Zhengdong et al.,1997), and also due to the ability to crystallize in non-centrosymmetric structures. Among several organic compounds reported for NLO properties, chalcone derivatives are noticeable materials for their excellent blue light transmittance and good crystallizability. They provide a necessary configuration to show NLO property with two planar rings connected through a conjugated double bond (Indira et al., 2002). Substitution on either of the phenyl rings greatly influence noncentrosymmetric crystal packing.
A variety of organic NLO materials, aromatic compounds with delocalized π-electron systems and a large dipole moment have been synthesized to improve the non-linear susceptibilities larger than the inorganic optical materials (Chemla et al., 1987;Lakshmana et al., 2002). Recently, new chalcones which can find use as promising materials in photonics industries, have been synthesized and their second-harmonic generation efficiency was studied (Sarojini et al., 2006). In the present paper, we report the synthesis and the crystal structure of the trimethoxyphenyl-4-hydroxycoumarin chalcone (see Scheme).
The structure study shows intramolecular and intermolecular hydrogen bonds of the type C-H···O contributing to the cohesion of the crystal.

Experimental
It was established that the condensation of the borate complexes of acyl(hydroxy)coumarins (Traven et al., 2007) with carboxylic acid anhydrides led to exclusive annulation of the α-pyrone ring. First, we prepare the borate complex of 4-hydroxycoumarin by the reaction of boron trifluoride etherate (1 g, 7.3 mmol) with the 3-acetyl-4-hydroxycoumarin (1.5 g, 7.3 mmol) in toluene (25 ml). Then the new chalcone of coumarin, containing annulated α-pyrone ring, was obtained by reaction of the borate complex of acyl(hydroxy) coumarin (1 g, 3.9 mmol) with 3, 4, 5 trimethoxyphenylaldehyde (0.78 g, 3.9 mmol) in presence of piperidine (Fig. 2). By recrystallizing the crude product in chloroform (30 ml) we tried to remove BF 2 OH from the complex and a pale yellow crystals with appropriate formula were appeared. Yield: 1.26 g (85%). The hydrogen atoms are fixed geometrically with the exception of the H4 where it is located from electron density difference map and is refined isotropically. In the absence of significant anomalous scattering, the absolute configuration could not be reliably determined and then the Friedel pairs were merged and any references to the Flack parameter were removed. Fig. 1. View of the title compound with atomic numbering. All atoms are shown with displacement ellipsoids drawn at the 50% probability level.   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 > σ(F 2 ) is used only for calculating Rfactors(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.