Internuclear cyclisation. Part XXVII. Further studies on the aromatisation of spirocyclohexadienyl dimers

Abstract

The formation and pyrolysis of a series of spirocyclohexadienyl dimers related to the bis-(spirodiene-lactam)(1) has been reinvestigated, and the scope of the reactions has been extended. The pyrolyses give phenanthridinones by a radical mechanism in which ring-expansion involves nitrogen migration and not aryl migration as previously reported. The effects of substituents on the ease of dissociation of the dimers, and on the ease of the nitrogen migration are briefly considered.