Methyl (2Z)-2-[(2-formyl-3-methyl-1H-indol-1-yl)methyl]-3-(4-methoxyphenyl)prop-2-enoate

In the title indole derivative, C22H21NO4, the dihedral angle between the benzene and pyrrole rings of indole moiety is 1.8 (1)°. The plane of the 4-methoxyphenyl ring is oriented with a dihedral angle of 60.7 (1)° with respect to the plane of the indole moiety. The molecular packing is stabilized by C—H⋯O hydrogen bonds which form a V-shaped chain arrangement along the bc plane of the unit cell. In addition to this, C—H⋯π and π–π interactions [centroid–centroid distances = 3.8102 (11) and 3.8803(12) Å], which run along the b-axis direction, stabilize the molecular packing.


Comment
Indole is the parent substance of a large number of important compounds that occur in nature with significant biological activity (Kaushik et al., 2013). Indole derivatives exhibit antibacterial, antifungal (Singh et al., 2000), antitumour (Andreani et al., 2001), antidepressant (Grinev et al., 1984) and anti-inflammatory (Rodriguez et al., 1985) activities. In view of that importance, we have undertaken the crystal structure determination of the title compound, and the results are presented here.
The X-ray study confirmed the molecular structure and atomic connectivity for (I), as illustrated in Fig. 1. The geometry of the indole ring system in the present structure is comparable with the related reported structure (Selvanayagam et al., 2008). Fig. 2 shows a superposition of the indole ring system of (I) with this related reported structure, using Qmol (Gans & Shalloway, 2001); the r.m.s. deviation is 0.016 Å.
In addition to the van der Waals interactions, the molecular structure is influenced by intramolecular C-H···O interactions (Table 1). In the molecular packing, two C-H···O hydrogen bonds form a V-shaped chain arrangement along ′bc′ plane of the unit cell (Fig. 3). In addition to this weak C-H···π and π···π interactions stabilizes the molecular packing ( Fig. 4 and Fig. 5).

Experimental
POCl 3 (1 ml) was added drop wise with stirring to DMF (4.25 ml) at 10-20°C over 20 minutes. Then (E)-methyl 4-(3methyl-1H-indol-1-yl)-3-(4-methoxy phenyl)but-2-enoate (1 g) in DMF (3 ml) was added slowly with stirring and the mixture was heated. Excess concentrated aqueous solution of NaOAc was added. The mixture was stirred for 30 minutes at 28°C and extracted with AcOEt (3x20ml). The dried (MgSO 4 ) extract after removal of solvent furnished a pale yellow oil (1.10 g), which was chromatographed on a silica gel column. Elution with light petroleum-ether/ethyl acetate (3:1) afforded the product in 80% yield. Single crystals of (I) were obtained by slow evaporation of methanol solution of the title compound at room temperature.

Refinement
H atoms were placed in idealized positions and allowed to ride on their parent atoms, with C-H distances of 0.93-0.96 Å, and U iso (H) = 1.5U eq (methyl C) and U iso (H) = 1.2U eq for other C atoms.

Figure 1
The molecular structure of the title compound, showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level.