Approaches to the synthesis of azonia-azulenes

Abstract

Two approaches to the azonia-azulenium system are described.
In Part I the preparation of a number of azepinoindoles by the thermal decomposition of 2-azidodiphenylmethanes is described. The usual products were lOH-azepino[l.2-a]indoles and the compound previously reported as llH-azepino[l,2-a]indole has been shown to exist in the tautomeric lOH-form. In one case steric obstruction led to the formation of a 6H- and an 8H-azepinoindole, and when a 2'-methoxyl group was present in the azide the major products were acridines and acridans. A mechanism is proposed which satisfactorily accounts for the observed products.
l-(2-Azidophenyl)-1-phenylethanol decomposed to give some 2-acetyldiphenylamine showing another nitrene insertion.
pathway. Photolytic decomposition of 2-azidodiphenylmethane gave the azo-compound. Azepino[l.2-a]indol-8-one has been prepared in good yield and converted into hydroxy- and ethoxyazepino[l,2-a]indolium salts.
In Part II the reduction of indolizine and some substituted indolizines by dissolving metals is shown to give dihydro- and tetrahydroindolizines. Attempts to add carbenes to dihydroindolizines and thus to produce the 5,7 ring system of the azonia-azulenes by ring expansion were unsuccessful.