Palladium-Catalyzed Multicomponent Synthesis of Phenanthridines

Significance

Reported is a three-component synthesis of substituted phenanthridines from aryl iodides, anilides, and methyl vinyl ketone (MVK). The reaction involves a sequential coupling of ortho-substituted aryl iodides with N-trifluoroacetylated ortho-bromoanilines, followed by insertion of MVK), aza-Michael cyclization and retro-Mannich reaction. The last step occurs with a sacrificial elimination of acetone to furnish the desired phenanthridines. The sequence is catalyzed by the simple Catellani system of palladium acetate (catalytic) and norbornene (equimolar). The yields range from moderate to excellent and the substrate scope was well studied in terms of aryl ­iodides, less so with the anilines. It was also possible to use methyl and t-butyl acrylates in place of MVK, leading to the elimination of methyl and t-butyl acetate, respectively.