Synthesis and crystal structure of N-(4-chlorophenyl)-5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidin-2-amine

The title compound, N-(4-chlorophenyl)-5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidin-2-amine, was synthesized by cyclization of 1-(4,6-dimethylpyrimidin-2-yl)-4-phenylthiosemicarbazide in the presence of Ni(NO3)2. In the crystal, molecules form inversion dimers via pairs of N—H⋯N hydrogen bonds, which are packed into layers by π-stacking interactions between the aromatic systems of neighbouring molecules.


Chemical context
It is well known that thermal cyclization of 1-(pyrymidin-2yl)thiosemicarbazides leads to the formation of mercapto derivatives of triazolopyrimidine (Babichev & Kovtunenko, 1977;Kottke & Kuhmshtedt, 1978). In contrast to this, it has been shown that analogous substrates can be converted into the corresponding 2-R-amino-5,7-dimethyl[1,2,4]triazolo-[1,5-a]pyrimidines by cyclization in the presence of methyl iodide and sodium acetate in boiling ethanol solution. Such processes undergo alcylation of a sulfur atom with the formation of the S-methyl derivative, which then undergoes intramolecular cyclization with elimination of a methanethiol molecule and the formation of the unstable intermediate A.
The subsequent Dimroth rearrangement of intermediate A gives the final product B (Fig. 1) (Vas'kevich et al., 2006). In the present work we show that an analogous cyclization followed by Dimroth rearrangement can proceed in mild conditions in the presence of Ni 2+ ions (Fig. 1).

Synthesis and crystallization
A warm solution of Ni(NO 3 ) 2 (0.0364 g, 0.125 mmol in 15 ml of ethanol) was added dropwise under vigorous stirring to a warm solution of 1-(4,6-dimethylpyrimidin-2-yl)-4-phenylthiosemicarbazide (0.0767 g, 0.25 mmol in 20 ml of ethanol), prepared according to a known procedure (Vas'kevich et al., 2006). An orange precipitate of the Ni 2+ complex (M:L = 1:2) was formed. The resulting mixture was left for a few days. Detailed analysis of the obtained compound showed the presence of a significant amount of colourless plate-shaped crystals of the title compound, which were used for X-ray analysis.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. All H atoms bonded to C atoms were placed in geometrically idealized positions according to hybridization and constrained to ride on their parent C atoms, with C-H bonds for the aromatic rings and methyl groups of 0.95 and 0.98 Å , respectively, with U iso (H aromatic ) = 1.2U eq (C) and U iso (H methyl ) = 1.5U eq (C). The methyl groups were allowed to rotate freely about the C-C bonds. The H atom bonded to the N atom was located in a difference map and refined without any restraints.  Table 1 Hydrogen-bond geometry (Å , ). (14) 173.5 (16) Symmetry code: (i) Àx þ 1; Ày; Àz þ 2.

Figure 2
The molecular structure of the title compound. Displacement ellipsoids are drawn at the 50% probability level. Packing diagram of the title compound withinteractions between aromatic systems represented by dashed lines. The projection is shown along [100]. H atoms have been omitted for clarity.

N-(4-Chlorophenyl)-5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidin-2-amine
Crystal data 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 > 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.