Synthesis of Phenanthridines via Palladium/Norbornene Catalysis

Significance

Reported is the synthesis of phenanthridines 3 from the reaction of benzyl­amines 2 with aryl iodides 1 by a palladium/­norbornene-catalyzed domino sequence (Catellani reaction; see Review below) via an intramolecular amination followed by an oxidative dehydrogenation. Optimization studies showed that the Catellani reaction proceeded most efficiently in the presence of Pd(OAc)₂, Ph₃P and 0.5 equivalent of norbornene. The use of three equivalents of norbornene was required for the provision of phenanthridines 3 as the major products, while 0.5 equivalent of norbornene afforded compounds 4, which required oxidative dehydrogenation to generate the phenanthridines. The reaction was extended to a series of aryl iodides 1. Iodides bearing ortho-EWGs led to lower yields than those with ortho-EDGs. Both EDG and EWG benzyl­amine substituents were tolerated by the reaction conditions. A plausible mechanism was proposed without evidence.