Alkylation of 5-phenyl-6R-2Н-1,2,4-triazine-3-thione and heterocyclization of 1-(4-bromophenyl)-2-(5-phenyl-6R-1,2,4-triazine-3-ylsulfanyl)ethanones

5,6-Diphenyl-1,2,4-triazine-3-thione and 5-phenyl-2,3-dihydro-1,2,4-triazine-3-thione were obtained by condensation of dibenzoyl (benzyl) and phenylglyoxal, respectively, with thiosemicarbazide (or its hydrochloride). Alkylation of 5,6-diphenyl-1,2,4-triazine-3-thione and 5-phenyl-2,3-dihydro-1,2,4-triazine-3-thione with p -bromophenacyl bromide in acetonitrile (acetone) in the presence of triethylamine proceeded to give 1-(4-bromophenyl)-2-(5-phenyl-(5,6-diphenyl-)- 1,2,4-triazine-3-ylsulfanyl)ethanones. 5,6-Diphenyl-1,2,4-triazine-3-thione was also alkylated by monochloroacetic acid and its methyl ester. It should be noted that the product of the abovementioned alkylation reaction was obtained in a higher yield with the use of the K2CO3-H2O-DMF system. The 1H NMR spectra of S-derivatives of 5-phenyl-(5,6-diphenyl-)- 1,2,4-triazine-3-thiones contained signals of the SCH2 protons in the range of δ 4.04-5.01 ppm as well as aromatic protons of the phenyl rings manifested as a multiplet at δ 7.23-7.50 ppm. The aromatic protons of the p -bromophenacyl group were observed as two signals shifted downfield at δ 7.77-7.83 and δ 8.02-8.06 ppm. The IR spectra of S-derivatives of 5-phenyl-6R-1,2,4-triazine-3-thiones contained intense bands of the С=О group at 1700, 1681, 1680, 1740 cm-1. The action of concentrated sulfuric acid on 1-(4-bromophenyl)-2-(5,6-diphenyl-1,2,4-triazine-3-ylsulfanyl)ethanone led to an intramolecular addition to the carbonyl group followed by dehydration and formation of 3-(4-bromophenyl)-6,7-diphenyl-8а- Н -[1,3]thiazolo[3,2- b ][1,2,4]triazine-8-ol, as evidenced by the 1H NMR data. The 1H NMR spectrum of the latter compound revealed no signals of the SCH2 protons, and the H-2 proton appeared as the signal shifted downfield (δ 6.78 ppm). 3-(4-Bromophenyl)-7-phenyl[1,3]thiazolo[3`,2`;2,3][1,2,4]triazinium hydrosulfate was synthesized by the intramolecular heterocyclization of 1-(4-bromophenyl)-2-(5-phenyl-1,2,4-triazine-3-ylsulfanyl)-ethanone under the action of concentrated sulfuric acid. The 1H NMR spectrum of 3-(4-bromophenyl)-7-phenyl[1,3]thiazolo[3`,2`;2,3][1,2,4]triazinium hydrosulfate contained the characteristic signal at δ 8.96 ppm attributed to the aromatic H-2 proton of the thiazole cycle. In addition, the cyclization reaction was evidenced by the shift of the H-6 proton signal to a weaker field (δ 10.29 ppm) compared with the corresponding proton signal of the starting compound, which could be caused by the appearance of a positively charged nitrogen atom in the structure. It is also pertinent to note that the IR spectra of the heterocyclization products revealed no absorption band of the carbonyl group, in contrast to the IR spectra of the initial 1-bromophenyl-2-(1,2,4-triazine-3-ylsulfanyl)ethanones.