Weakly Coordinating, Ketone-Directed (η -Pentamethylcyclopentadienyl)cobalt(III)- and (η -Pentamethylcyclopentadienyl)rhodium(III)-Catalyzed C-H Amidation of Arenes: A Route to Acridone Alkaloids.

The weakly coordinating, ketone-directed, regioselective monoamidation of aromatic ketones, chalcone, carbazole, and benzophenones was achieved by employing high-valent cobalt and rhodium catalysis to access numerous biologically important molecular building blocks. This amidation proceeded smoothly with a variety of ketones and several amidating partners. The application of the products in the synthesis of various heterocycles, including acridones, indoles, quinoline, quinolones, quinolinones, and quinazolines, was also explored. The total synthesis of acridone-based alkaloids, namely, toddaliopsin A, toddaliopsin D, and arborinine, and the formal synthesis of acronycine and noracronycin were also accomplished by applying this method. A mechanistic study revealed this amidation reaction follows a base-assisted intermolecular electrophilic substitution pathway.