(E)-2-(3,4-Dimethoxybenzylidene)-5,6-dimethoxy-2,3-dihydro-1H-inden-1-one

In the title compound, C20H20O5, the 2,3-dihydro-1H-indene ring system is essentially planar [maximum deviation = 0.010 (1) Å] and is inclined at an angle of 4.09 (4)° with respect to the phenyl ring. The C=C bond has an E configuration. In the crystal, the molecules are linked into chains propagating in [102] via intermolecular C—H⋯O hydrogen bonds. The crystal structure is further consolidated by C—H⋯π interactions.

In the title compound, C 20 H 20 O 5 , the 2,3-dihydro-1H-indene ring system is essentially planar [maximum deviation = 0.010 (1) Å ] and is inclined at an angle of 4.09 (4) with respect to the phenyl ring. The C C bond has an E configuration. In the crystal, the molecules are linked into chains propagating in [102] via intermolecular C-HÁ Á ÁO hydrogen bonds. The crystal structure is further consolidated by C-HÁ Á Á interactions.

Comment
Chalcones are a chemical class that has shown promising therapeutic efficacy for the management of several diseases. Many papers have been presented in the literature with references to structural modifications of the chalcone template (Nielsen et al., 1998). In fact, not many other structural templates can claim association with such a diverse range of pharmacological activities, among which cytotoxicity, antitumour, anti-inflammatory, antiplasmodial, immunosuppression and antioxidant, are widely cited (Go et al., 2005). They considered as the precursor of flavonoids and isoflavonoids. Chemically they consisted of open chain flavonoid by a three carbon α, β-unsaturated carbonyl system (Nowakowska, 2007). In fact, the pharmacological properties of chalcones are due to the presence of both α, β-unsaturation (Furusawa et al., 2005) and an aromatic ring.
In the title molecule ( Fig. 1), the 2,3-dihydro-1H-indene (C1-C9) ring system is essentially planar (maximum deviation = 0.010 (1) Å for atom C7) and is inclined at an angle of 4.09 (4) ° with the phenyl ring (C11-C16), which indicates they are almost parallel to each other. The crystal structure determination shows the E configuration of the C9═C10 and confirms that the molecule adopts an overall planar conformation, with the exception of the methyl moieties. Bond lengths (Allen et al., 1987) and angles are within normal ranges.

Experimental
A mixture of 5,6-dimethoxy-2,3-dihydro-1H-indene-1-one (0.001 mmol) and 3,4-dimethoxy benzaldehyde (0.001 mmol) were dissolved in methanol (10 mL) and 30% sodium hydroxide solution (5 mL) was added and stirred for 5 h. After completion of the reaction as evident from TLC (thin layer chromatography), the mixture was poured into crushed ice then neutralized with concentrated HCl. The precipitated solid was filtered, washed with water and recrystallised from ethanol to reveal yellow plates of (I).

Refinement
All H atoms were positioned geometrically and refined using a riding model with C-H = 0.93-0.97 Å and U iso (H) = 1.2 or 1.5 U eq (C). A rotating-group model was applied for the methyl groups. The highest residual electron density peak is located at 0.69 Å from C6 and the deepest hole is located at 1.13 Å from C7. Fig. 1. The molecular structure of the title compound showing 50% probability displacement ellipsoids for non-H atoms.

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cyrosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K.
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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.