1-[1-(2,1,3-Benzoxadiazol-5-ylmethyl)-1H-1,2,3-triazol-4-yl]hexan-1-one

The title compound, C15H17N5O2, was synthesized as part of a series of benzoxadiazole analogs which were examined for fluorescent properties by Cu-catalysed azide–alkyne cycloaddition (CuAAC) of a 4-azidomethyl-benzoxadiazole substrate. The structure shows a nearly coplanar orientation of the hexanone keto group and the 1,2,3-triazole ring [dihedral angle = 4.3 (3)°], while the benzoxadiazole and triazole groups are much more severely inclined [dihedral angle = 70.87 (4)°]. In the crystal, weak C—H⋯N interactions connect translationally-related triazole rings, while another set of C—H⋯N interactions is formed between inversion-related benzoxadiazole units, forming a three-dimensional network. The crystal studied was a non-merohedral twin with refined value of the twin fraction of 0.2289 (16).


Comment
In an effort to explore benzoxadiazole derivatives with interesting spectroscopic properties, we generated the title compound, I, for comparison to its parent 4-azidomethyl-benzoxadiazole (II). Although we observed large changes in the spectra of substrates with an azido group conjugated to the chromophore, derivatives with an intervening methylene group tended to have only small changes upon triazole formation (Key & Cairo, 2011). Compound I was synthesized unintentionally through the use of an oxidized sample of n-octyne which also contained oct-1-yn-3-one as an impurity.
Copper sulfate (7 mg, 0.046 mmol, 0.2 equiv) and ascorbic acid (12 mg, 0.068 mmol, 0.3 equiv) were then added to the solution. The reaction mixture was allowed to stir at room temperature for approximately 1 h, forming a red precipitate.
The precipitate was filtered off and the product was obtained after purification by column chromatography

Refinement
The crystal used for data collection was found to display non-merohedral twinning. Both components of the twin were CELL_NOW. Integrated intensities for the reflections from the two components were written into a SHELXL-97 HKLF 5 reflection file with the program TWINABS (Bruker, 2008), using all reflection data (exactly overlapped, partially overlapped and non-overlapped). The reflection (1 0 0) was found to have an excessively high disagreement between F o and F c , and was omitted from the refinement. The refined value of the twin fraction (SHELXL-97 BASF parameter) was 0.2289 (16). All H atoms were generated in idealized positions and refined using a riding model with fixed C-H distances (C-H aromatic = 0.95 Å, C-H methylene = 0.99 Å, C-H methyl = 0.98 Å) and with U iso (H) = 1.2U eq (C).    Table 1).

Figure 3
Compounds used in this study.

Special details
Geometry. All standard uncertainties (s.u.'s) (except the s.u. in the dihedral angle between two least-squares planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'s involving least-squares 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.