Chromatographic-mass spectrometric study of the reaction pathway of 4-methyl-8-phenyl-3-tosyl-1,4-dihydropyrazolo[5,1-c][1,2,4]triazine with 2-chloro-N-(4-methoxyphenyl)acetamide

Abstract

As part of a study of the reactivity and properties of partially hydrogenated condensed as-triazines, a study of the reaction route between 4-methyl-3-tosyl-8-phenyl-1,4-dihydropyrazolo[5,1-c][1,2,4]triazine and 2-chloro-N-(4-methoxyphenyl)acetamide in a K₂CO₃-N,N-dimethylformamide (DMF) medium was carried out using the HPLC-MS method in combination with UV detection on an Agilent Technologies 1260 infinity instrument with an Agilent 6230 TOF LC/MS mass detector. Integrated scanned chromatograms of the total ion current of the reaction mixtures were obtained immediately after mixing the reagents, as well as at 5, 10, and 20 minutes of the process. These chromatograms were used to interpret the signals based on pre-calculated masses in the form of molecular ions with [M+H]⁺ of the starting and theoretically expected intermediates and the resulting substances. Additional structural identification of the reaction products was performed using thin-layer chromatography with UV detection, NMR spectroscopy (on ¹³C and ¹H nuclei, including using their two-dimensional correlations), and IR spectroscopy. It was found that the interaction of the starting components involves two main pathways of transformations leading to different rearrangements of the as-triazine ring. The preferred pathway of the reaction is reduced to a cascade process, during which a condensed pyrimidine ring is constructed with the formation of a functionally substituted pyrazolo[1,5-a]pyrimidine. Another direction of the reaction is as-triazine ring contraction with the formation of an imidazolo[1,2-b]pyrazole derivative. It was also found that prolonged heating of the reaction mixture is undesirable, since it leads to the formation of formylation products due to the use of DMF as a solvent. Thus, in the course of the study, the key reaction intermediates (in particular, 2-((1-(1-cyanoethyl)-4-phenyl-1H-pyrazol-5-yl)imino)-N-(4-methoxyphenyl)acetamide) and by-products (tricyclic derivatives of pyrazolo[1,5-a]pyrimido[5,4-d]pyrimidin-4(1H)-ones, functionally substituted imidazolo[1,2-b]pyrazole) were identified; optimal process conditions were selected. The approach presented in the article can be used in the development of methods for the synthesis and proof of the reaction mechanism during the construction of new functional materials (drugs, dyes, fluorescent probes, etc.) based on condensed as-triazine and pyrimidine systems.