DIAZABICYCLOALKANES WITH NITROGEN ATOMS IN THE NODAL POSITIONS. 4. INTRAMOLECULAR CYCLIZATION OF N-(β-X-ETHYL)-1,2,3,4-TETRAHYDROQUINOXALINES AND BEHAVIOR OF BENZO-1,4-DIAZABICYCLOOCTENES IN ACIDIC MEDIA

Article abstract of DOI:10.1007/BF00553710

The intramolecular cyclization of N-(β-hydroxyethyl)-N'-acetyl-1,2,3,4-tetrahydroquinoxaline in refluxing HBr was investigated by liquid microcolumn chromatography.Under these conditions the amide group undergoes rapid hydrolysis, the hydroxy groups undergo relatively slow exchange by bromine, and the resulting N-(β-bromoethyl)-1,2,3,4-tetrahydroquinoxaline undergoes cyclization to give benzo-1,4-diazabicyclo<2.2.2>octene.These transformations terminate with the establishment of equilibrium between VII and I. 7-Methyl-N-(β-chloroethyl)-1,2,3,4-tetrahydroquinoxaline similarly forms an equilibrium reaction mixture in HBr.The effect of various factors (the acid and bromide ion concentrations, the character of the acid, and the temperature) on the position of the equilibrium of the compounds obtained and on the occurence of side reactions (hydrolysis and dealkylation) was studied.