Metal ions and complexes in organic reactions. Part XVII. Iron(II)-promoted conversions of nuclear-substituted anilinopyridines into pyridoquinoxalines

Abstract

Brief heating of o-nitro-substituted anilinopyridines with iron(II) oxalate at ∼280° resulted in 5–40% conversion into cyclised products; traces of azo-compounds and of unidentified dimers were also isolated. Two of the five isomeric nitro-amines thus tested gave pyrido[3,4-b]quinoxaline (1), one gave pyrido[2,3-b]quinoxaline (2), and one gave a mixture of the two. The procedure was applied to syntheses of pyridoquinoxalines containing a methyl or methoxy-group in the benzo-ring; in some of these cases cyclisation gave a mixture of isomers or occurred with displacement of a methoxy- or methyl group. N.m.r. and other spectral features of the pyridoquinoxalines are reported.