Synthesis and tautomeric transformations of 2-(tert-butyl)-1,2,4-benzotriazine-3(2H)-thiones

Abstract

Treatment of 2 (tert butyl) 1,2,3,4 benzotetrazinium tetrafluoroborates with sodium thio cyanate afforded 2 (tert butylazo)phenyl isothiocyanates 3, which exist in equilibrium with 2 (tert butyl) 1,2,4 benzotriazine 3(2H ) thiones 3´. The equilibrium depends on the sub stituents R in the benzene ring: the percentage of the open isomer 3 is about 20% for R = H or Me; for R = Cl or Br, the equilibrium is completely shifted to cyclic isomer 3´. The equilibrium is slow on the time scale of the 1 H and 13 C NMR experiments. For com pounds 3a/3´a (R = H), the spectra at 24 °C show two sets of signals, while those at 0 °C contain only signals for isomer 3´a.

The synthesis of 1,2,4-benzotriazines

“…In early work by Haddadin and Issidorides, benzofuroxan (59) and diethylamine gave o-benzoquinone dioxime (60) and the imine (61). The two products interacted to form the imine oxide intermediate (62) which was converted into 3-methyl-1,2,4-benzotriazine (39) and 1-hydroxy-2-methylbenzoimidazole 3-oxide (63) (Scheme 8). 50 Scheme 8.…”

“…Next, isothiocyanates ( 111) was converted into the benzotriazinethiones (112) upon ring closure (Scheme 18). 62 Scheme 18. Synthesis and tautomeric transformations of 2-(t-butyl)-1,2,4-benzotriazine-3(2H)-thiones (112).…”