(E)-3-(9-Ethyl-9H-carbazol-3-yl)-1-(2-methoxyphenyl)prop-2-en-1-one

In the title molecule, C24H21NO2, the dihedral angle between the carbazole ring system [with a maximum deviation of 0.052 (2) Å] and the benzene ring is 38.6 (1)°. In the crystal, weak bifurcated (C—H)2⋯O hydrogen bonds link the molecules into chains along [100].


Comment
The title compound (I) exhibits potential tubulin polymerization-inhibiting activity in drug discovery (Caulfield et al., 2002). It was obtained by reacting 1-(2-methoxyphenyl)ethanone and 9-ethyl-9H-carbazole-3-carbaldehyde through a modified procedure from Mazimba et al. (2011). The molecular structure of (I) is shown in Fig. 1. The fused ring system and the benzene ring are linked via an α,β-unsaturated carbonyl group so that the molecule has the potential to contain an extended π-conjugation system. However, there is distortion from a planar conformation, which is reflected in the dihedral angle between the carbazole ring system (with a maximum deviation of 0.052 (2)Å for C10) and the benzene ring which is 38.6 (1)°. The α, β-unsaturated carbonyl group is close to planar with a torsion angle of -4.2 (3)° for C15-C16-C17-O1 and forms a dihedral angle of 7.9 (1)° with the carbazole group, indicating some π conjugation between these two groups. A similar structure has been reported where the methoxy group on the benzene ring is substituted by a hydroxyl group (Cao et al., 2005). In this hydroxyl derivative the molecule is more planar, with a dihedral angle of 11.58 (12)° between the planes of the carbazole ring system and benzene ring. Also in the hydroxyl derivative, the hydroxyl group is involved in an intramolecular hydrogen bond with the oxygen atom of the ketone group. In molecule (I), the methoxy group is on the opposite side of the molecule from the ketone group as a result of an approximate 180° rotation about the C17-C18 bond, possibly to avoid steric interactions between atoms O1 and O2. In the crystal, weak bifurcated (C-H) 2 ···O hydrogen bonds link molecules into chains along [100] (Fig. 2).

Experimental
All chemicals used were purchased from commercial sources and used without further purification. To a solution of 1-(2methoxyphenyl)ethanone (1.5 g, 10 mmol) and 9-ethyl-9H-carbazole-3-carbaldehyde (2.23 g, 10 mmol) in MeOH (20 ml) was added 50% KOH (4 ml) aqueous solution dropwise with continuous stirring at room temperature. The reaction mixture was then refluxed for 4 h. The reaction suspension was poured onto cold H 2 O and the mixture was neutralized with 2 M HCl until the solution was acidic. A yellow solid was precipitated out, collected and washed with H 2 O. This solid was characterized by NMR to be the title compound. Crystals were grown from MeOH/H 2 O (50:1 v/v) solution by slow evaporation.

Refinement
For each methyl group, the hydrogen atoms were added in calculated positions using a riding-model with C-H = 0.98 Å and U(H) = 1.5U eq (C). The torsion angle, which defines the orientation of the methyl group about the C-C or O-C bond, was refined. The rest of the hydrogen atoms were included in calculated positions using a riding-model approximation with C-H = 0.95 to 0.99 Å and U iso (H) = 1.2U eq (C).

Figure 1
The molecular structure of (I) with displacement ellipsoids drawn at the 50% probability level (arbitrary spheres for the H atoms).

Crystal data
C 24 H 21 NO 2 M r = 355.42 Orthorhombic, Pbca Hall symbol: -P 2ac 2ab a = 15.9332 (7)  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.16 e Å −3 Δρ min = −0.14 e Å −3 Special details Experimental. All work was done at 150 K using an Oxford Cryosystems Cryostream Cooler. The data collection strategy was set up to measure a quadrant of reciprocal space with a redundancy factor of 3.0, which means that 90% of the data was measured at least 3.0 times. Phi and omega scans with a frame width of 0.9 degree were used. Data integration was done with DENZO, and scaling and merging of the data was done with SCALEPACK. 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. For each methyl group, the hydrogen atoms were added at calculated positions using a riding model with U(H) = 1.5 * U eq (bonded carbon atom). The torsion angle, which defines the orientation of the methyl group about the C -C or O-C bond, was refined. The rest of the hydrogen atoms were included in the model at calculated positions using a riding model with U(H) = 1.2 * U eq (bonded atom).