N-Cyclopentyl-N-(3-oxo-2,3-dihydro-1H-inden-1-yl)acetamide

The title molecule, C16H19NO2, consists of an indane moiety, which is connected through an N atom to an acetamide group and a cyclopentane ring. The N atom adopts planar triangular geometry. Intermolecular interactions, such as π–π stacking or hydrogen bonding, were not observed.


Tao Zhang, Tom McCabe, Bartosz Marzec, Neil Frankish and Helen Sheridan Comment
The indane pharmacophore occurs in many different bioactive molecules. Indinavir, a HIV-1 inhibitor is a protease inhibitor in clinical use that contains an indane fragment (Vaccva et al., 1994). Nivemedone, a nitro-indanone has antiallergenic activity (Buckle et al., 1973) while many simple indanols demonstrate bronchodilatory activity (Heinzelmann et al., 1940). We have demonstrated that indanone derivatives possess smooth muscle relaxant activity and inhibit mediator release (Sheridan et al., 1990(Sheridan et al., , 1999a(Sheridan et al., , 1999bFrankish et al., 2004). In a recent study on bioactivity we evaluated the smooth muscle relaxant activity and mediator release inhibition activities demonstrated by a series of aminoindanones (Simplício et al., 2004;Sheridan et al., 2008).
The asymmetric unit of the compound presented in this paper contains a single molecule of N-cyclopentyl-N-(3oxo-2,3-dihydro-1H -inden-1-yl)acetamide. The geometry around the nitrogen atom can be best described as trigonal planar. As there are no flexible hydrogen atoms attached to the nitrogen atom N1 or the oxygen atoms (O1 and O2) hydrogen bonding do not prevail in the title compound. The shortest distance between the aromatic rings is 4.150 (9) Å and cannot be considered as the π-π stacking interaction.
The packing diagram of the structure, presented in Fig. 2, shows that the molecules are separated and when viewed along the crystallographic a-axis seem to form a sheet-like structure in the ab-plane. These sheets pack in the direction of the crystallographic c-axis. The shortest separation distance between them is 4.243 (75) Å and a weak Van der Vaals force or an electrostatic interaction may be responsible for holding the sheets together.
The solvent was removed in vacuo and the residue was purified directly by flash column chromatography on silica gel (eluant, pet. ether:EtOAc, 4:1). After evaporation of the eluent the secondary amine was isolated as an oil (175 mg, 86%).
To this secondary amine solution (700 mg, 3.25 mmol) in DCM (5 ml) was added triethylamine (657 mg, 0.90 ml, 6.51 mmol), acetic anhydride (664 mg, 0.61 ml, 6.51 mmol) and DMAP (476 mg, 3.90 mmol). The reaction was stirred at room temperature for 2 h. The reaction mixture was then washed with water, dried over Na 2 SO 4 , filtered and evaporated in vacuo. The residue was purified by column chromatography over silica gel (pet. ether:EtOAc, 4:1) to yield the title compound as a white solid (450 mg, 54%). Crystals suitable for X-ray diffraction were obtained after 5 days of slow evaporation of an ethanol solution.

Refinement
All H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms with C-H = 0.93 Å for aromatic H atoms, 0.96 Å for CH 3 type H atoms, 0.97 Å for CH 2 type H atoms and 0.98 Å for CH type H atoms, respectively. U iso (H) values were set at 1.5U eq (C) for methyl H atoms, and 1.2U eq (C)for the rest of the H atoms.

Figure 1
The molecular structure of the title compound with the atom numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. H atoms are presented as small spheres of arbitrary radius.  Packing diagram of the title compound viewed along the crystallographic a-axis. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.21 e Å −3 Δρ min = −0.23 e Å −3

Special details
Experimental. The su's on the Cell Angles were measured. 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq O2 0.31603 (