Syntheses of nitrogen-containing heterocyclic compounds. XXIX. An improved method for the preparation of 10H-pyrido[3,2-b][1,4]benzoxazine (1-azaphenoxazine).

Abstract

Syntheses of 10H-pyrido [3, 2-b] [1, 4] and 5H-pyrido [3, 4-b] [1, 4] benzoxazine (1 and 3) were carried out by the cyclization reaction of 2-and 4-(2'-hydroxyanilino)-3-nitropyridines (7 and 9) in dimethylformamide in the presence of sodium hydroxide. This method is an improvement over the past reports that this kind of anilino compounds are difficult to undergo intramolecular cyclization because they have an intramolecular hydrogen bonding properties. 3-Substituted (methyl, chloro, bromo, nitro), 7-nitro, and 8-methyl derivatives of 10H-pyrido [3, 2-b] [1, 4] benzoxazine (1a-1f) were synthesized in a high yield by the application of this method. The anilino compound was obtained by the selective condensation of 2-chloro-3-nitro-5-substituted pyridine and o-aminophenol in ethanol in the presence of copper and sodium hydroxide. However, 5H-pyrido [2, 3-b] [1, 4] benzoxazine (4) was not obtained from 3-(2'-nitroanilino)-2-pyridone (10) in this sodium hydroxide-dimethylformamide system, while 5H-pyrido [2, 3-b] [1, 4] and 10H-pyrido [4, 3-b] [1, 4] benzoxazine (4 and 2) were synthesized by the cyclization of 2- and 4-(2'-bromophenoxy)-3-(N-formylamino) pyridines (13 and 17), respectively, in xylene in the presence of copper and potassium carbonate.