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Synthesis of Phenanthridines via Palladium/Norbornene Catalysis
G. Maestri, M.-H. Larraufie, E. Derat, C. Ollivier, L. Fensterbank*, E. Lacôte*, M. Malacria*
Université Pierre et Marie Curie, Paris, France
16 February 2011 (online)
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.