6-(3,5-Dimethyl-1H-pyrazol-1-yl)-1,2,4,5-tetrazin-3(2H)-one

The title compound, C7H8N6O, represents the keto form and adopts a nearly planar structure (r.m.s. deviation of the non-H atoms = 0.072 Å). In the crystal, molecules form spiral chains along the c axis by N—H⋯N hydrogen bonds. The chains are linked to each other by weak C—H⋯O hydrogen bonds, forming a three-dimensional framework.

Upon a refluxing of compound 1 with amine 2 and K 2 CO 3 in acetonitrile and following treatment with water, an step required to workup of the reaction mixture, it was found that instead of introduction of N-nucleophile (with a formation of compound 3) the reaction gave the hydroxy derivative 4′ (Figure 1).

Experimental
The X-ray quality crystals of the title compound were grown by slow evaporation of acetonitrile solution.
All the reagents were of analytical grade, purchased from commercial sources, and used as received. Infrared spectra were determined in KBr pellets on a Perkin-Elmer Model 577 spectrometer. Mass-spectra were recorded on a Varian MAT-311 A instrument. The 1 H, 13 C and 15 N NMR spectra (external standard: CH 3 NO 2 ) were recorded at 300.13, 75.47 and 50.7 MHz, respectively. The chemical shift values (δ, p.p.m.) are expressed relative to the chemical shift of the solvent-d or to external standard without correction nitromethane ( 14 N and 15 N). Melting points were determined on Gallenkamp melting point apparatus and are uncorrected.

Refinement
The hydrogen atom of the NH group was found in difference Fourier synthesis and refined in isotropic approximation.
The H(C) atomic positions were calculated and refined in isotropic approximation in riding model with the U iso (H) parameters equal to 1.5 U eq (Ci), 1.2 U eq (Cj), where U eq (Ci) and U eq (Cj) are the equivalent thermal parameters of the methyl carbon atoms and all the other carbon atoms, respectively, to which corresponding H atoms are bonded.

Figure 1
Synthesis of the title compound.   Crystal packing fragment of the title compound. Hydrogen atoms of the methyl groups are omitted for clarity. Dashed lines indicate the intermolecular N-H···N and C-H···O hydrogen bonds. 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.