Synthesis of polynuclear heterocycles. Part II. Cyclisations of 2- and 4-substituted 3-amino- and 3-nitro-pyridines

Abstract

Treatment of 2- and 4-phenoxy-3-nitropyridine with triethyl phosphite failed to yield the expected pyridobenz-oxazines; 2- and 4-phenylthio-3-nitropyridine, however, cyclised to give 5H-pyrido [2,3-b][1,4] benzothiazine and 5H-pyrido[3,4-b][1,4]benzothiazine respectively, albeit in poor yield. Similar results were obtained by thermolytic decomposition of the corresponding 2- and 4-substituted 3-azido-pyridines. 9-Hydroxypyrido[2,3-b] 1,4,5-benzoxadiazepine has been synthesised.

An improved synthesis of pyrido [2,3-c]furoxan is reported, and its n.m.r. spectrum has been measured at various temperatures. Attempts to prepare the unknown isomeric pyrido [3,4-c]furoxan have failed.