Propyl 2-(1H-indol-3-yl)acetate

In the title compound, C13H15NO2, the acetate group [C—C(=O)—O] makes a dihedral angle of 62.35 (13)° with the mean plane of the indole ring system [maximum deviation = 0.011 (3) Å]. In the crystal, molecules are linked by N—H⋯O hydrogen bonds, forming helical chains propagating along [010].


Related literature
For the use of the title compound as a starting material for the synthesis of platinum complexes with antitumor activity, see: Kim et al. (1994). For its use as an intermediate in organic synthesis, see: Pandey et al. (1997). For the synthesis of indole-3-acetic acid, see: Johnson & Donald (1973). For standard bond-length data, see: Allen et al. (1987).  Table 1 Hydrogen-bond geometry (Å , ).

Comment
Indole derivatives are some of the most effective anticancer agents currently available. The title compound is a starting material for the synthesis of platinum complexes with antitumor activity (Kim et al., 1994) and is also an important intermediate in organic synthesis (Pandey et al., 1997). As part of our studies of the synthesis and characterization of such compounds, we herein report on the crystal structure of the title compound.
The molecular structure of the title compound is shown in Fig In the crystal, molecules are linked by N-H···O hydrogen bonds forming helical chains propagating along the b axis direction (Table 1 and Fig 2).

Experimental
Indole-3-acetic acid was synthesized following a literature procedure (Johnson & Donald, 1973). The title compound was synthesized by adding indole-3-acetic acid (10 g, 0.057 mol) and 100 mL of dichloromethane to a three-neck flask with stirring and cooled in an ice bath. 4.3 mL of thionyl chloride was added drop wise, after the solution was stirred for a further 10 min. 15 mL of 1-propanol was then added and the reaction was followed using TLC until completion. The title compound was obtained as a light yellow solid [Yield = 10.5 g, 0.048 mol]. Recrystallization with ethanol gave yellow block-like crystals, suitable for X-ray diffraction analysis.

Refinement
H atoms were positioned geometrically (N-H = 0.86 Å, C-H = 0.93, 0.97 and 0.96 Å for CH, CH 2 and CH 3 H atoms, respectively) and refined as riding atoms with U iso (H) = 1.5U eq (C-methyl) and = 1.2U eq (N,C) for other H atoms.  The molecular structure of the title molecule, with atom labelling. The displacement ellipsoids are drawn at the 30% probability level.

Figure 2
A view along the a axis of the crystal packing of the title compound. The hydrogen bonds are shown as dashed lines (see Table 1 for details). 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.