Morgan‐Walls Cyclization

Abstract The synthesis of phenanthridine derivatives by means of the treatment ofN‐acylortho‐aminobiphenyls with ZnCl2at high temperature or with POCl3is generally referred to as the Pictet–Hubert phenanthridine synthesis. The study finds that modification is unsuccessful for the transformation ofortho‐formamidobiphenyl itself to the parent phenanthridine scaffold and nitrobenzene and HBF4have been used to catalyze such a cyclization. This modification is known as Morgan–Walls cyclization. This reaction has been applied for the synthesis of phenanthridine derivatives, especially for 6‐substituted phenanthridines.