A reaction of 3 benzylthiotriazole 4 amines with aromatic aldehydes leads to the formation of 6,7 dihydro 5H [1,2,4]triazolo[3,4 b][1,3,4]thiadiazines. A dihydrothiadiazine ring opening along the N-N bond occurs by the action of strong bases. open ing, 2 [(1,2,4 triazol 3 yl)thio]ethanimine, X ray crystallography. 5H [1,2,4]triazolo[3,4 b][1,3,4]thiadiazine (2b). The yield was 79%, m.p. 280 °C. Found (%): C, 53.26; H, 3.09; N, 14.00. C 22 H 16 BrN 5 O 2 S. Calculated (%): C, 53.45; H, 3.26; N, 14.17. 1 H NMR (DMSO d 6 ), δ: 5.0 (dd, 1 H, H(6), J = 10.0 Hz, J = 10.4 Hz); 5.2 (d, 1 H, H(7), J = 10.0 Hz); 7.26 (d, 2 H, Ar, J = 8.4 Hz); 7.42-7.47 (m, 5 H, Ph, Ar); 7.51 (d, 1 H, NH, J = 10.4 Hz); 7.71, 8.11 (both d, 2 H each, Ar, J = 8.6 Hz); 7.91-7.97 (m, 2 H, Ph). MS (EI, 70 eV), m/z (I rel (%)): 495 [M] + 98). 6,7 Di(4 nitrophenyl) 3 phenyl 6,7 dihydro 5H [1,2,4]tri azolo[3,4 b][1,3,4]thiadiazine (2c). The yield was 38%, m.p. 260 °C. Found (%): C, 57.63; H, 3.72; N, 18.11. C 22 H 16 N 6 O 4 S. Calculated (%): C, 57.39; H, 3.50; N, 18.25. 1 H NMR (DMSO d 6 ), δ: 5.18-5.35 (m, 2 H, H(6), H(7)); 7.46 (m, 3 H, Ph); 7.58 (d, 2 H, Ar, J = 8.8 Hz); 7.67 (d, 1 H, NH, J = 10.1 Hz); 7.74 (d, 2 H, Ar, J = 8.7 Hz); 7.95 (m, 2 H, Ph); 8.12 (m, 4 H, Ar). MS (EI, 70 eV), m/z (I rel (%)): 293 (. 6 (3 Nitrophenyl) 7 (4 nitrophenyl) 3 (pyridin 4 yl) 6,7 di hydro 5H [1,2,4]triazolo[3,4 b][1,3,4]thiadiazine (2d).