The thermolysis of polyazapentadienes. Part 2. Formation of quinoxalines from 5-aryl-1-phenyl-1,2,5-triazapentadienes

Abstract

Thermolysis in the gas phase of 5-(p-substituted phenyl)-1-phenyl-1,2,5-triazapentadienes at 600 °C and 10^–2 Torr gives 6-substituted quinoxalines. The yield is ca. 30%, and is independent of the electronic nature of the substituent. The corresponding 5-(o-substituted) derivatives give 5-substituted quinoxalines, though the yield is lower, and quinoxaline itself is a major contaminant, due to ipso attack and ejection of the substituent. 5-(m-Substituted) derivatives give mixtures of 5- and 6-substituted quinoxalines on pyrolysis. The 5-isomer is dominant for compounds with m-alkyl substituents, while the 6-isomer is the major product for those with electron-withdrawing or electron-donating m-substituents.