Crystal structures of two (±)-exo-N-isobornylacetamides

The title compounds consist of a 1,7,7-trimethylbicyclo[2.2.1]heptane (bornane or camphane) skeleton which is decorated with acetamide for (±)-(1) and chloroacetamide for (±)-(2), functionalities. In the crystals of both compounds, molecules are linked via N—H⋯O hydrogen bonds, reinforced by C—H⋯O contacts, forming chains propagating along the a axis.


Chemical context
Isobornylamine-derived amides have recently been described as useful antimycobacterial agents (Stavrakov et al., 2014a,b). Promising biological activity profiles have been also discovered for other bornane derivatives such as 2-arylbornanes (Duclos et al., 2008), camphor oximes (Schenone et al., 2000), bornyl (3,4,5-trihydroxy)-cinnamate (Steinbrecher et al., 2008) and others. There is no doubt that isobornylamine derivatives are chemically related to terpenoids camphor (Seebaluck et al., 2015) and borneol (Horvá thová et al., 2012), which are well known for their biological activities. On the other hand, compounds containing the bornane skeleton are frequently used as chiral building blocks for various ligands, catalysts and chiral auxiliaries (Chelucci, 2006;Langlois & Kouklovsky, 2009;Ramó n & Yus, 2007). In light of the aforementioned facts, there is a vast interest in developing new synthetic protocols for the synthesis of compounds of this class and in their structural studies. We have recently reported an application of the Ritter reaction (Jiang et al., 2014) in the synthesis of amide-derivatized heterocycles (Turks et al., 2012). Hence, we identified the possibility to obtain isobornylamine derived amides (AE)-(1) and (AE)-(2) from borneol in the direct Ritter reaction. When the optically active (À)-borneol was submitted to standard Ritter reaction conditions, the expected compounds were isolated in acceptable yields albeit in the racemic form. A similar type of racemization due to a 6,2hydride shift was described in the Ritter reaction of (À)bornyl acetate (Hanzawa et al., 2012.). Previously, compounds (AE)-(1) and (AE)-(2) have been obtained as side products in a ISSN 2056-9890 cationic rearrangement of (À)--pinene in the presence of the corresponding nitriles (Ung et al., 2014).

Supramolecular features
In the crystals of both compounds, molecules are linked by N-HÁ Á ÁO hydrogen bonds, reinforced by C-HÁ Á ÁO contacts, forming trans-amide chains propagating along the a axis direction (Figs. 3 and 4 and Tables 1 and 2

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. For both compounds, the H atom on the amino group were located in difference Fourier maps and freely refined, and the C-bound H atoms were positioned geometrically and refined as riding on their parent atoms: C-H = 0.93-0.97 Å with U iso (H) = 1.5U eq (C) for methyl H atoms and 1.2U eq (C) for other H atoms. Reflection (0,1,1) whose intensity was affected by the beam-stop was removed from the final refinement of compound (AE)-(1). The crystal packing of compound (AE)-(1), viewed along the b axis. Hydrogen bonds are shown as dashed lines (see Table 1 for details). For clarity, only H atoms involved in these interactions have been included.

Figure 4
The crystal packing of compound (AE)-(2), viewed along the b axis. Hydrogen bonds are shown as dashed lines (see Table 2 for details). For clarity, only H atoms involved in these interactions have been included.

Computing details
For both compounds, data collection: KappaCCD Server Software (Nonius, 1997); cell refinement: SCALEPACK (Otwinowski & Minor, 1997); data reduction: DENZO and SCALEPACK (Otwinowski & Minor, 1997); program(s) used to solve structure: SIR2011 (Burla et al., 2012); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012) and Mercury (Macrae et al., 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008), PLATON (Spek, 2009) and publCIF (Westrip, 2010). 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.

Special details
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.