Continuing our studies on synthesis of derivatives in the sym-triazine series based on 2-azido-4,6-disubstituted 1,35-triazines [1-3] by reactions of compounds 1a-d with methyl cyanoacetate and ethyl cyanoacetate, we obtained derivatives of a novel coupled heterocyclic system: 2-[1,3,5]triazin-2-yl-1,2-dihydro[1,2,3,4]tetrazine-5-carboxylic acid esters 2a-d. a R 1 = NH 2 , R 2 = NEt 2 ; b R 1 = R 2 = NMe 2 ; c R 1 = PhNMe, R 2 = NMe 2 ; d R 1 = NH 2 , R 2 = piperidino; a, b R 3 = Me, c, d R 3 = EtThe IR spectra were recorded in nujol mulls of the samples on a Specord IR-75 spectrometer. The 1 H NMR spectra were recorded on a Bruker DRX-500 spectrometer (500 MHz) in DMSO-d 6 , internal standard TMS. The mass spectra were taken on a Finnigan MAT INCOS50 (ionizing radiation energy, 70 eV). TLC was run on Silufol UV-250 plates in the system 1:1 acetone-hexane.(4-Amino-6-diethylamino[1,3,5]triazin-2-yl)-1,2-dihydro[1,2,3,4]tetrazine-5-carboxylic Acid 2-Methyl Ester (2a). A solution of Na (0.16 g, 7.2 mmol) in methanol (5 ml) was added in small portions at room temperature with stirring to a solution containing 2-amino-4-(diethylamino)-6-azido-1,3,5-triazine (1 g, 4.8 mmol) and methyl cyanoacetate (0.48 g, 4.8 mmol) in absolute methanol (10 ml). Then the reaction mixture was stirred for another 30 min at the same temperature, and then it was boiled for 1 h and cooled down. The solvent was evaporated down to 2/3 volume, and then it was diluted with ice water (50 ml). Then it was acidified with 50% acetic acid to pH 7; the precipitate formed was separated, washed until the wash water tested neutral, and dried in air. The product was recrystallized from alcohol. Yield 1.25 g (85%); mp, 223-224°C. __________________________________________________________________________________________