Direct synthesis of 3-aryl-1,2,4,5-tetrazine N-1-oxides by the oxidation with methyl(trifluoromethyl)dioxirane

Article abstract of DOI:10.1016/0040-4020(95)01063-7

1,2,4,5-Tetrazines are oxidized by methyl(trifluoromethyl)dioxirane (TFD) to their hitherto unknown N-oxides in excellent yields. A detailed NMR study (¹H, ¹³C, ¹⁵N) shows that the N-1 atom of 3-aryl-1,2,4,5-tetrazines 1 is oxidized regioselectively. A Hammett plot (r² = 0.970) affords a ρ value of -1.53. The correlation of the logarithm of the reaction rates versus the ionization potentials, which were calculated by AM1, is much worse for ionization out of the aromatic system (IP(π); r² = 0.804) than for ionization out of the higher-energy nitrogen lone pairs (IP(N:); r² = 0.940). This implies that an electron transfer mechanism is unlikely and an S(N)2 attack by the nitrogen lone pair of the tetrazine on the dioxirane peroxide bond appears to operate.