6-Methyl-4-oxo-4H-chromene-3-carbaldehyde

In the title compound, C11H8O3, the benzopyran-4-one or chromone ring system is almost planar, with a maximum deviation of 0.045 (2) Å. The crystal structure is stablized by π–π interactions between the benzene and pyran rings of inversion-related molecules stacked along the b axis, with a centroid–centroid distance of 3.5463 (12) Å

In the title compound, C 11 H 8 O 3 , the benzopyran-4-one or chromone ring system is almost planar, with a maximum deviation of 0.045 (2) Å . The crystal structure is stablized by interactions between the benzene and pyran rings of inversion-related molecules stacked along the b axis, with a centroid-centroid distance of 3.5463 (12) Å

Comment
Chromone is a heterocyclic compound containing a benzene ring fused with a pyran ring, so it is also called as benzopyran-4-one. Chromone moieties are associated with various physiological and biological properties such as antibacterial (Patel et al., 2011), antioxidant (Gautam et al., 2010;Hassan et al., 1992), antianaphylactic (Nohara et al., 1974), antiinflammatory (Khan et al., 2010), anticancer (Ishar et al., 2006), and thymidine phosphorylase inhibitor (Khan et al., 2009) activities. The title compound is a chromone derivative synthesized as a part of our ongoing research to study different biological activities of this medicinally important class of organic compounds and establish their structureactivity relationship.
The structure of title compound ( Fig. 1) is composed of a planar chromone moiety (O1/C1-C9) with maximum deviation of 0.045 (2) Å for atom C8. Bond lengths and angles are similar to those observed in a structurally related compound (Wang & Kong, 2007). In the crystal (Fig. 2), inversion-related molecules are linked along the b axis by significant π-π stacking interactions occurring between benzene and pyran rings of chromone moeities, with centroidcentroid distances of 3.5463 (12) Å.

Experimental
The title compound was synthesized by taking dry dimethylformamide (12.32 ml) into a three necked flask followed by slow addition of POCl 3 (49 mmol) with intensive stirring at 50°C. Heating and stirring was continued for 2 h at 45-55°C.
A solution of 5-methyl-2-hydroxyacetophenone (10 mmol) in DMF was then slowly added under stirring at 50°C. The stirring was continued for additional 2 h at 55-60°C. After cooling, the mixture was kept over night at room temperature and diluted slowly by adding crushed ice (300 g) and stirred again for 6 h to obtain the crude product. Recrystallization from ethanol afforded crystals in 78.7% yield (1.48 g) which were found suitable for single-crystal X-ray diffraction studies. All chemicals were purchased by sigma Aldrich Germany.

Refinement
H atoms were positioned geometrically with C-H = 0.93-0.95 Å and constrained to ride on their parent atoms with U iso (H)= 1.5U eq (CH 3 ) or 1.2U eq (CH).

Figure 2
The crystal packing of the title compound viewed along the a axis. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.26 e Å −3 Δρ min = −0.19 e Å −3 Extinction correction: SHELXTL (Sheldrick, 2008), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.013 (9) Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > σ(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.