Synthesis and study of the azide-tetrazole tautomerism in 2-azido-4-(trifluoromethyl)-6-R-pyrimidines (R = H, 4-ClC6H4)

Azide-tetrazole equilibrium in azidopyrimidines bearing trifluoromethyl group on the example of 2-azidopyrimidines has been studied. The latter were synthesized via nitrosation of 2-hydrazino-4-trifluoromethylpyrimidine and reaction of NaN3 with 4-trifluoromethyl-2- chloro-6-(4-chlorophenyl)pyrimidine. The tautomeric equilibrium 5-trifluoro methyl tetrazolo[1,5-a]pyrimidine ⇆ 2-azido-4-trifluoromethylpyrimidine was observed in the absence of solvent and in DMSO-d6 solution, whereas in CDCl3 only an azide form exists. For 2-azido- 4-trifluoromethyl-6-(4-chlorophenyl)pyrimidine, only an azide isomer was detected in CDCl3 solution, and in DMSO-d6 solution it is in equilibrium with 5-(trifluoromethyl)-7-(4-chlorophenyl) tetrazolo[1,5-a]pyrimidine (the tautomer ratio is 99 : 1). Thermodynamic and kinetic parameters of 5-trifluoromethyltetrazolo[1,5-a]pyrimidine ⇆ 2-azido-4-trifluoromethylpyri midine tautomeric rearrangement in DMSO-d6 for 5-trifluoromethyltetrazolo[1,5-a]pyrimidine were determined using the exchange spectroscopy (EXSY) technique.