The reactions of 5-R-6-aryl-3-(2-pyridyl)-1,2,4-triazines with a 4,5-dimethylaryne intermediate generated in situ, which had not previously been used for this purpose, was studied. The reaction outcome depends on the nature of the substituent at the C5 position of 1,2,4-triazine: the introduction of electron-donating substituents leads to the preferential domino transformation of the 3-(2-pyridyl)-1,2,4-triazine system with the formation of 2,3-dimethyl-10-(1,2,3-triazol-3-yl)pyrido[1,2-a]indoles, and electron-withdrawing ones leads to the formation of the corresponding 6,7-dimethylisoquinolines. The main difference between dimethylaryne and its unsubstituted analogue is a significant increase in the proportion of isoquinolines in the reaction products when 5,6-diaryl-3-(2-pyridyl)-1,2,4-triazines are used as substrates. © 2023, Pleiades Publishing, Ltd.