A novel heterocyclic system — dihydro-2H-1,5,2,4-dioxadiazine. 2,4-Dimethyldihydro-2H-1,5,2,4-dioxadiazine hydrochloride: synthesis and NMR study

The first representative of a novel heterocyclic system, namely, 2,4-dimethyldihydro-2H-1,5,2,4-dioxadiazine hydrochloride, was synthesized.     

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

Treatment of 2-(tert-butyl)-1,2,3,4-benzotetrazinium tetrafluoroborates with sodium thiocyanate 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 substituents 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 ¹H and ¹³C NMR experiments. For compounds 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. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1192–1195, July, 2006.     

The tert-butyl-NNO-azoxy group in the synthesis of 1,2,4-benzotriazin-3(4H)-one 1-oxides

Treatment of 2-(tert-butyl-NNO-azoxy)anilines with phosgene at 20 °C was proposed as a novel route to 1,2,4-benzotriazin-3(4H )-one 1-oxides. This method involves a new reaction, viz., an intramolecular interaction of the tert-butyl-NNO-azoxy group with a C-electrophile (leading to the formation of the N(2)—C(3) bond of the triazine ring) followed by elimination of the tert-butyl group. Complete assignment of the signals in the ¹H and ¹³C NMR spectra of the compounds obtained was performed. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1507–1509, August, 2007.     

Release of nitrosating species in the course of reduction of benzo-1,2,3,4-tetrazine 1,3-dioxides

[reaction: see text] The reduction of benzo-1,2,3,4-tetrazine 1,3-dioxides (BTDOs) 1 with Na(2)S(2)O(4) or SnCl(2) is suggested to proceed via intermediate N-nitrosobenzotriazoles 3 to afford benzotriazoles 2. The (15)N-labeling experiments exhibit that the N-3 atom of the tetrazine ring is incorporated into the nitroso group of 3 that is ultimately released into solution. It is possible that the biological activity of BTDOs is due to their ability to release nitrosating species, i.e., N-nitrosotriazol 3 or HNO(2), in the course of reduction.     

Oxidative N-nitration of secondary amines

Reaction of secondary amines with the nitrite anion assisted by diacetoxyiodobenzene results in respective N-nitroamines. It is the first example of oxidative nitration of the amino group. N-Nitrosoamines are by-products. The yields and the ratio of the nitration and nitrosation products depend on the nature of the starting amine, cation of the salt used, and the solvent.     

Intramolecular interaction between ortho-azido and azoxy groups as a new way of forming a N—N bond. Synthesis of 2-alkylbenzotriazole 1-oxides

Heating of 2-(alkyl-NNO-azoxy)-1-azidobenzenes in boiling benzene gave 2-alkyl-benzotriazole 1-oxides (Alk = Me, Et, Prⁱ, and Bu^t). This first-order reaction involves an earlier unknown intramolecular interaction between the azido and azoxy groups with simultaneous release of molecular nitrogen. The cyclization rate increases in the following sequence of the alkyl groups: Me < Et < Prⁱ < Bu^t. Complete assignment of the signals in the ¹H, ¹³C, and ¹⁴N NMR spectra of 2-alkylbenzotriazole 1-oxides was performed. Dedicated to Corresponding Member of the Russian Academy of Sciences E. P. Serebryakov on the occasion of his 70th birthday. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 989–996, April, 2005.     

Preparation of a single-phase solid electrolyte La1 ? xSrxGa1 ? yMgyO3 ? (x + y)/2 by self-propagating high-temperature synthesis

Highly dispersed single-phase powders described as La_0.88Sr_0.12Ga_0.82Mg_0.18O_2.85 were prepared using a method based on the principles of self-propagating high-temperature synthesis (SHS). Lanthanum, strontium, gallium, and magnesium nitrates were used in the SHS as “oxidants”, and ethylene glycol was used as the reducing agent. The initial reaction mixture was liquid. According to X-ray diffraction and scanning electron microscopy data, the sample becomes a single phase after annealing of the primary SHS product at 1200°C, which is substantially lower than in other synthetic methods. Using so active powders (grain size of about 100–130 nm), it is possible to reduce the temperature of the final annealing of the ceramics to 1275°C, which gives rise to single-phase finely dispersed ceramics having specific properties.