Ring-closure to phenanthridines and acridines of some 2-arylaminomethylene derivatives of cyclohexanone and 1-tetralone

Abstract

Ring-closure of 2-(naphthylaminomethylene)cyclohexanones affords either the derived tetrahydrobenzophenanthridine or the isomeric tetrahydrobenzacridine. Ring-closure with formic acid gave a preponderance of the phenanthridine but other reagents favoured formation of the acridine. An intermediate rearrangement of the Hofmann-Martius type may account for the formation of the acridines.

The formation of 5,6,8,9-tetrahydrodibenz[c,h]acridine in the ring-closure of 2-anilinomethylene-1-tetralone with formic acid has been confirmed and an explanation of this observation is presented, but similar ring-closure of 2-(1-naphthylaminomethylene)-1-tetralone gave 7,8-dihydrodibenzo[c,k]phenanthridine.