CH functionalization has recently attracted considerable attention in organic synthesis. Although it provides the same products as already well established cross-coupling methodologies, it has the advantage of avoiding the use of metallic species such as Grignard, boron, silicon, and tin compounds. Thus, regarding both atom and step economy, the formation of carbon–carbon bonds through CH functionalization is a convenient methodology with broad application in total synthesis and medicinal chemistry.
Phenanthridinones are key core units found in many natural products which exhibit interesting biological and pharmaceutical properties. In the last years, novel alternative synthetic approaches have been developed to the synthesis of the phenanthridinone core and related lactams. The palladium-catalyzed intramolecular direct CH arylation reaction has proved to be one of the most efficient method for the access to such valuable compounds. However, relative big amounts of catalysts are usually required. Herein, we report an unprecedented palladium-catalyzed intramolecular direct arylation for the general access of phenanthridinones under very low catalyst loadings. With only 0.05 mol%, a palladium NCP pincer complex promotes efficiently the direct functionalization of a series of N-arylbenzanilides and N-arylsulfonamides which constitutes an effective, versatil and environmentally attractive procedure for the preparation of phenanthridinones, biaryl sultams and related heterocyclic derivatives.