Synthesis and study of azide-tetrazole tautomerism in 2-azido-6-phenylpyrimidin-4(3H)-one and 2-azido-4-chloro-6-phenylpyrimidine

Azide-tetrazole equilibrium in 2-azido-6-phenylpyrimidin-4(3 H )-one and 2-azido-4-chloro-6-phenylpyrimidine was studied by IR spectroscopy and 1 H and 13 C NMR spectroscopy in a comparison with the published data. For 2-azido-6-phenylpyrimidin-4(3 H )-one isolated from a weakly acidic solution, 1 H NMR (DMSO-d6) spectroscopy revealed a three-component equilibrium between azide (A) and tetrazole (T and T ′) forms T ⇆ A ⇆ T ′ (82: 10: 8) immediately after dissolution and a two-component equilibrium T ⇆ T ′ (12: 88) in an equilibrium state. For the precipitate recrystallized from ethanol, the T ⇆ T ′ equilibrium was observed. The structures of both tautomers were confirmed by X-ray diffraction analysis. 2-Azido-4-chloro-6-phenylpyrimidine existed predominantly in the azide form and the A ⇆ T (94: 6) equilibrium was found only in the DMSO-d 6 solution.