Weakly Coordinating Ketone-Directed Cp*Co(III)- and Cp*Rh(III)-Catalyzed C-H Amidation of Arenes: A Route to Acridone Alkaloids.

Weakly coordinating, ketone-directed, regioselective mono-amidation of aromatic ketones, chalcone, carbazole, and benzophenones are achieved employing high-valent cobalt- and rhodium-catalysis to access numerous biologically important molecular building blocks. This amidation proceeds smoothly with varieties of ketones as well as with several amidating partners. The application of the products to the syntheses of heterocycles acridones, indoles, quinoline, quinolones, quinolinones, and quinazolines is also described. The total syntheses of acridone based alkaloids, namely toddaliopsin A, toddaliopsin D, arborinine, and formal syntheses of acronycine and noracronycin have also been accomplished applying this method. The mechanistic study reveals this amidation reaction follows a base assisted intermolecular electrophilic substitution (BIES) pathway.