Reinvestigation of the reaction of 3-substituted 1,2,4-triazines with nitronate anions: unexpected behavior of 3-(2-ethoxyphenyl)-1,2,4-triazine in the reaction with anions of nitroalkanes

Abstract

3-Substituted 1,2,4-triazines easily react with nitronate anions to replace hydrogen atom in the position C-5 according to nucleophilic substitution mechanism and form appropriate oximes of 5-formyl- or 5-acyl-1,2,4-triazines. Present study has shown that the course of the reaction strongly depends on the structure of the substituent in the position C-3 of 1,2,4-triazine ring. Thus, 2-ethoxyphenyl substituent in 1,2,4-triazine allowed to form, besides appropriate oximes, also new nitronic acid derivatives stabilized by intramolecular hydrogen bonds. The synthesis pathway and molecular structures of oximes were confirmed by X-ray analysis performed for model compound 1-[3-(2-ethoxyphenyl)-1,2,4-triazin-5-yl]ethanone oxime. The presence of the new nitronic acid derivatives in the reaction mixture and the theoretical calculations at DFT/B3LYP/6-311++G(d,p) level strongly suggest that intermediate stabilized by bifurcated intramolecular hydrogen bond is a common intermediate for the construction of appropriate oximes.