Crystal structure and Hirshfeld surface analysis of N-(tert-butyl)-2-(phenylethynyl)imidazo[1,2-a]pyridin-3-amine

In the title compound, the phenyl ring of the phenyl-ethynyl substituent is inclined to the mean plane of the imidazo[1,2-a]pyridine moiety by 18.2 (1)°.


Chemical context
Compounds containing the imidazo[1,2-a]pyridine moiety have received considerable attention because of their interesting biological activities. For instance, it is found in several commercialized drugs such as the sedative Zolpidem, the anxiolytics Alpidem, Saridipem and Necopidem, the heartfailure drug Olprinone and the antiulcer drug Zolimidine (Baviskar et al., 2011). As a continuation of our research on nitrogen-bridgehead heterocycles (Tber et al., 2015), we report herein on the molecular and crystal structures, along with the Hirshfeld surface analysis, of the title compound, N-(tertbutyl)-2-(phenylethynyl)imidazo[1,2-a]pyridin-3-amine.

Supramolecular features
In the crystal, molecules are connected into chains along the caxis direction by N3-H3AÁ Á ÁN1 i hydrogen bonds (Table 1 and Fig. 2). These chains are linked by C2-H2Á Á ÁCg4 ii and C17-H17CÁ Á ÁCg3 iii interactions, forming slabs parallel to the ac plane ( Fig. 3 and Table 1).

Hirshfeld surface analysis
The Hirshfield surface analysis (Spackman & Jayatilaka, 2009;McKinnon et al., 2007) was carried out using Crystal-Explorer17.5 (Turner et al., 2017). The Hirshfeld surfaces and their associated two-dimensional fingerprint plots were used to quantify the various intermolecular interactions in the title compound. The molecular Hirshfeld surfaces were generated using a standard (high) surface resolution with the threedimensional d norm surfaces mapped over a fixed colour scale of À0.379 (red) to 1.341 (blue). The red spots on the surface indicate the intermolecular contacts involved in the hydrogen bonds. Fig. 4a illustrates the intermolecular N-HÁ Á ÁN hydrogen bonding of the title compound with d norm mapped on Hirshfeld surface, and the C-HÁ Á Á(ring) contacts are visualized in Fig. 4b. The fingerprint plots are given in Fig. 5. They reveal that the principal intermolecular interactions are HÁ Á ÁH at 54.0% (Fig. 5b) and CÁ Á ÁH/HÁ Á ÁC at 35.6% (Fig. 5c), followed by NÁ Á ÁH/HÁ Á ÁN interactions at 10.2% (Fig. 5d).  Table 1 Hydrogen-bond geometry (Å , ).

Figure 2
A partial view along the a axis of the crystal packing of the title compound, showing the N-HÁ Á ÁN hydrogen-bonded chains (dashed lines; Table 1). The C-bound H atoms have been omitted.

Figure 3
A view along the c axis of the crystal packing of the title compound. The C-HÁ Á Á(ring) interactions and N-HÁ Á ÁH hydrogen bonds (see Table 1) are indicated by dashed lines. Only the H atoms (grey balls) involved in the various intermolecular interactions have been included.

Figure 1
The molecular structure of the title compound, with atom labelling. Displacement ellipsoids are drawn at the 50% probability level.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The C-bound H atoms were placed in idealized positions and refined as riding: C-H = 0.93-0.96 Å with U iso (H) = 1.5U eq (C-methyl) and 1.2U eq (C) for other C-bound H atoms. The NH H atom was located in a difference-Fourier map. Its parameters were adjusted to give N-H = 0.89 Å and it was then refined as riding with U iso (H) = 1.2U eq (N). The crystal studied was refined as an inversion twin, with a final BASF value of 0.3 (6).

Funding information
The support of NSF-MRI grant No. 1228232 for the purchase of the diffractometer and Tulane University for support of the Tulane Crystallography Laboratory are gratefully acknowledged.        (9) Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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. Hatoms attached to carbon were placed in calculated positions (C-H = 0.93 -0.96 Å) while that attached to nitrogen was placed in a location derived from a difference map and its parameters adjusted to give N-H = 0.89 Å. All were included as riding contributions with isotropic displacement parameters 1.2 -1.5 times those of the attached atoms. Refined as a 2component inversion twin.